Transcript
INCREMENTAL FRYING OIL LIFE USING ADSORBENT COMBINATIONS
By Chatchalai Siasakul
A Master’s Report in Partial Fulfillment of the Requirement for the Degree MASTER OF SCIENCE Department of Food Technology Graduate School SILPAKORN UNIVERSITY 2005 ISBN 974-11-6210-3
การเพิ่มอายุนา้ํ มันทอดโดยใชสารดูดซับผสม
โดย นางชัชชลัยย เซี๊ยะสกุล
สารนิพนธนี้เปนสวนหนึ่งของการศึกษาตามหลักสูตรปริญญาวิทยาศาสตรมหาบัณฑิต สาขาวิชาเทคโนโลยีอาหาร ภาควิชาเทคโนโลยีอาหาร บัณฑิตวิทยาลัย มหาวิทยาลัยศิลปากร ปการศึกษา 2548 ISBN 974-11-6210-3 ลิขสิทธิ์ของบัณฑิตวิทยาลัย มหาวิทยาลัยศิลปากร
The graduate school, Silpakorn University accepted master report entitled “INCREMENTAL FRYING OIL LIFE USING ADSORBENT COMBINATIONS” by Chatchalai Siasakul in partial fulfillment of the requirement for the degree of master of science, program of food technology.
……………………………………………................ (Assoc.Prof.Wisa Chattiwat, Ph.D.) Vice President for Acadamic Affairs Acting Dean .……….../………...../………….
Master report Advisor Asst.Prof.Bhundit Innawong, Ph.D.
Master report committee ………………………………………………Chairman (Arunsri
Leejeerajumnean, Ph.D.)
………/………./………..
………………………………………………..Member (Asst.Prof.Bhundit
Innawong, Ph.D.)
………/………./………..
………………………………………………..Member (Suched Samuhaseneeto, Ph.D.) ………/………./………..
K 46403303: สาขาวิชาเทคโนโลยีอาหาร คําสําคัญ: การเพิ่มอายุน้ํามันทอด / สารดูดซับ / การเสื่อมเสียของน้ํามันทอด / ระบบการหมุนเวียนเติมน้ํามัน ชัชชลัยย เซี๊ยะสกุล: การเพิ่มอายุน้ํามันทอดโดยการใชสารดูดซับผสม (INCREMENTAL FRYING OIL LIFE USING ADSORBENT COMBINATIONS) อาจารยผูควบคุมสารนิพนธ: ผศ.ดร.บัณฑิต อินณวงศ, 74 หนา. ISBN 974-11-6210-3 การศึกษาผลการเพิ่มอายุน้ํามันในกระบวนการทอดที่มีการใชสารดูดซับผสมพบวา สารดูดซับผสมซึ่ง ประกอบดวยสารดูดซับผสม 2 ชุด คือ สารดูดซับผสมชุดที่1 (เบนโทไนต: ถานกัมมันต: ซีไรต ในอัตราสวน 3:4:1) และสารดูดซับผสมชุดที่ 2 (เบนโทไนต: ถานกัมมันต: ซีไรต ในอัตราสวน 3:4:1 + กรดซิตริก 1%) ตอ คุณลักษณะทางกายภาพและเคมีของน้ํามันในการทอดผลิตภัณฑนองไกชุบแปงทอด โดยเปรียบเทียบกับการ ทอดที่ไมไดใชสารดูดซับผสม พบวาการทอดที่มีการใชสารดูดซับผสมสงผลใหคาทางเคมีของน้ํามัน มีปริมาณ กรดไขมันอิสระ, คาเพอรออกไซด และคาความคงตัวทางไฟฟาลดลง (p≤0.05) สําหรับคุณลักษณะทางกายภาพ ของน้ํามันพบวา คาความสวางของน้ํามันที่มีการใชสารดูดซับผสมมีคาเพิ่มขึ้น (p≤0.05) อยางไรก็ตามน้ํามัน ทอดที่สุมเก็บจากทุก 3 ชั่วโมงการทอดที่มีการใชสารดูดซับผสม2 ชุดนั้นมีปริมาณกรดไขมันอิสระ, คาเพอร ออกไซด, และคาความคงตัวทางไฟฟาไมแตกตางกันอยางมีนัยสําคัญทางสถิติ (p≤0.05) ในขณะที่คาความสวาง ในน้ํามันทอดที่มีการใชสารดูดซับผสมชุดที่ 2 มีคาความสวางมากกวา (p≤0.05)น้ํามันทอดที่มีการใชสารดูดซับ ผสมชุดที่1 จึงไดมีการนําสารดูดซับผสมไปทําการศึกษาตอโดยศึกษารวมกับระบบการกรองและระบบการ หมุนเวียนเติมน้ํามัน (Oil replenishment) สําหรับผลการศึกษาการใชสารดูดซับผสมรวมกับระบบการหมุนเวียนเติมน้ํามัน (Oil replenishment) ตอคุณลักษณะทางกายภาพและเคมีของน้ํามันทอด โดยใชน้ํามันเริ่มตนที่คาปริมาณกรดไขมันอิสระประมาณ 1 พบวา การใชสารดูดซับผสมรวมกับระบบการกรองและการหมุนเวียนเติมน้ํามันชวยชะลอการเสื่อมสภาพของ น้ํามันทอดได (p≤0.05) การเปรียบเทียบผลที่ไดกับการทอดที่ไมไดใชการหมุนเวียนน้ํามัน พบวาปริมาณกรด ไขมันอิสระ, คาเพอรออกไซด, คาความคงตัวทางไฟฟา, และคาสี ในน้ํามันทอดลดลงอยางมีนับสําคัญทางสถิติ (p≤0.05) การนําน้ํามันที่ผานการทอดมีระดับคาความเปนกรดระดับ 1% เติมในการหมุนเวียนเติมน้ํามัน ความถี่ ทุก 2 ชั่วโมง ที่ระดับ 10%, 20%, 30% รวมกับการเติมสารดูดซับผสม พบวาที่ระดับการเติมน้ํามันสูงสุดมีผลตอ คุณภาพน้ํามันมากที่สุด การหมุนเวียนเติมน้ํามันที่ระดับ 20% และ 30% มีประสิทธิภาพในการขัดขวางการ เสื่อมสภาพของน้ํามันและการเกิดปฏิกิริยาออกซิเดชั่น เพราะวาน้ํามันที่เติมไปจะไปเจือจางสวนผสมตางๆที่สงผล ตอการเกิดปฏิกิริยาดังกลาวและยังไปกําจัดสารประกอบที่มีที่เกิดขึ้นในน้ํามันดังกลาว ภาควิชาเทคโนโลยีอาหาร บัณฑิตวิทยาลัย มหาวิทยาลัยศิลปากร ปการศึกษา 2548 ลายมือชื่อนักศึกษา.................................................................................................................................................... ลายมือชื่ออาจารยผูควบคุมสารนิพนธ................................................................................................................ .....
IV
K46403303: MAJOR: FOOD TECHNOLOGY KEY WORD: INCREMENT FRYING OIL / ADSORBENT / OIL DETERIORATION / OIL REPLENISHMENT CHATCHALAI SIASAKUL: INCREMENTAL FRYING OIL LIFE USING ADSORBENT COMBINATIONS. MASTER’S REPORT ADVISOR: ASST.PROF.DR.BHUNDIT INNAWONG, Ph.D. 74 P. ISBN 974-11-6210-3.
The effects of two different adsorbent combinations (com I; bentonite: activated carbon: celite = 3: 4: 1 and com II; bentonite: activated clay: celite = 3: 4:1 + 1%citric acid) used for prolonging and improving the oil life cycle on the physico-chemical changes of used oil were studied. The used oils were evaluated by refrying drum chicken in the used oil and then compared to the control. Treatments of used frying oils with adsorbent combination could reduce (p≤0.05) fatty acid (FFA), peroxide value (PV), and Food oil Sensor (FOS) reading. The oil treated with com I reduced % FFA, PV, and FOS reading by 44.31%,50.20%, and 40.12%, respectively, while as 41.61%, 44.86%,and 32.83%, respectively, for com II. The oil treated with com II exhibited (p≤0.05) the lighter color than com I. In addition, the colors of oils treated with com I and com II were bleached. The L*, a*, and b* changes of oil color were 30.70%, 1.69%, and 31.68% for com I and 53.19%, 19.11%, and 39.53% for com II, respectively. Thus, the next experiment of this study was conducted to determine the impacts of com II with oil replenishment on the changes in physico-chemical characteristics of used oils. Treatment of use frying oil with adsorbent combination and frequent replenishment were employed to improve the overall oil quality as indicating via free fatty acid (FFA) level, peroxide value (PV), FOS reading, and color parameters for L*, a*, and b*. The 1% acid value (AV) of used oil with three different amounts of replenishment (10%, 20%, and 30%) every 2 hr were investigated. The higher replenishment level applied, the more oil quality obtained. As expectation, all the oils treated with adsorbent addition and replenishment refreshed the oil color and decreased (p<0.05) FFA, PV, and FOS reading. In addition, the replenished oil with and 20% and 30% potentially retarded (p<0.05) the oil deterioration and oxidation because of the dilution effect and the removal of polar constitutes created in the abused oil. Department of Food Technology
Graduate School, Silpakorn University
Academic Year 2005
Student’s signature………………………………………………………………………………………….. Master’s report Advisor’s signature………………………………………………………………………....
V
ACKNOWLEDGEMENTS
I wish to express my sincere gratitude and respect to my advisor Asst.Prof.Dr.Bhundit Innawong for his kindness, ideas, patience, and knowledgeable advice throughout my master report. I am thankful for his willingness to take the time to make suggestions and help me to achieve my goals. His support, guidance, and encouragement were most appreciated. I thank Dr. Arunsri Leejeerajumnean, Dr. Suched Samuhaseneeto, Who express to the members of my master report. I would like to thank all of the graduate students that assisted in this research. I sincerely thank all staff in the department of Food Technology. Many thanks were extending to all my friends. A special thank to Miss Patchimaporn Udomkun, who helped me and suggested all good opinions. I would especially like to thank my parents for their love. I thank BETTER FOODS Co., Ltd. for their financial support and encouragement that they were giving me throughout my academic career. I thank all staffs in cooked product division of my manufacture for their assistance in all situations. Finally, I sincerely thank my beloved husband for his eternity love, consolation, and motivation that all make me accomplish my goals.
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TABLE OF CONTENTS Page THAI ABSTRACT………………………………………………………………......IV ENGLISH ABSTRACT………………………………………………………………V ACKNOWLEDGEMENTS ........................................................................................ VI LIST OF TABLES ...................................................................................................... IX LIST OF FIGURES .................................................................................................... XI CHAPTER 1
Introduction .......................................................................................................1 References .................................................................................................2
2
Literature reveiw ...............................................................................................3 Fundamental of Frying ..............................................................................3 Adsorbent Technology ............................................................................11 Utilization of Adsorbent in Frying Process.............................................18 References ...............................................................................................24
3
Utilization of mixed adsorbents to extend frying oil life cycle .......................26 Abstract ...................................................................................................26 Introduction .............................................................................................27 Materials and method ..............................................................................28 Results and discussion.............................................................................33 Conclusions .............................................................................................39 References ...............................................................................................39
4
Application of adsorbent and oil replenishment for prolonging useful oil life53 Abstract ...................................................................................................53 Introduction .............................................................................................54 Materials and method ..............................................................................55 Results and discussion.............................................................................59 Conclusions .............................................................................................61 References ...............................................................................................61
5
SUMMARY ....................................................................................................74
VII
Page VITA
.................................................................................................................75
VIII
LIST OF TABLES Table
Page
2.1
Degradation Reactions of Oil ..............................................................................6
2.2
Filtercorp oil data after filtration .......................................................................20
2.3
Free fatty acids in fryer oil with and without filtercorp pad filtration ..............21
2.4
Soap and Polar material content of the fryer oil................................................22
3.1
Changes in overall free fatty acid in untreated and treated used oil during frying 36 hr..................................................................................................................46
3.2
Changes in overall peroxide value in untreated and treated used oil during frying 36 hr........................................................................................................47
3.3
Changes in overall dielectric constant in untreated and treated used oil during frying 36 hr........................................................................................................48
3.4
Changes in overall lightness in untreated and treated used oil during frying 36 hr .......................................................................................................................49
3.5
Changes in overall redness in untreated and treated used oil during frying 36 hr ………………………………………………………………………………..50
3.6
Changes in overall yellowness in untreated and treated used oil during frying 36 hr..................................................................................................................51
3.7
Summary of improvement ability (%) of used frying oils at 18 hr and 36 hr with adsorbent combination..............................................................................52
4.1
FFA values for oil samples at different percentage oils replenishment with adsorbent combination and filtration system. ..................................................68
4.2
Peroxides values for oil samples at different percentage oils replenishment with adsorbent combination and filtration system............................................69
4.3
FOR reading values for oil samples at different percentage oils replenishment with adsorbent combination and filtration system............................................70
4.4
Lightness values for oil samples at different percentage oils replenishment with adsorbent combination and filtration system............................................71
4.5
Redness values for oil samples at different percentage oils replenishment with adsorbent combination and filtration system....................................................72
IX
Table
4.6
Page
Yellowness values for oil samples at different percentage oils replenishment with adsorbent combination and filtration system............................................73
X
LIST OF FIGURES Figure
Page
2.1
Sorption operations with solid-particle sorbents. ..............................................13
2.2
Structure of bentonite clay. ...............................................................................16
3.1
Electric fryer and portable filtration..................................................................31
3.2
The changes of free fatty acid in untreated and treated used oil during frying 36 hr...................................................................................................................42
3.3
The changes of peroxide value in untreated and treated used oil during frying 36 hr...................................................................................................................43
3.4
The changes of dielectric constant in untreated and treated used oil during frying 36 hr........................................................................................................44
3.5
The changes of quality parameters during 36 h of refrying with untreated oil and treated oil, where color parameters in Tintometer coordinates L*, a*, and b*. ......................................................................................................................45
4.1
Average FFA values obtained for oil samples at different percentage oils replenishment with adsorbent combination.......................................................64
4.2
Average PV values obtained for oil samples at different percentage oils replenishment with adsorbent combination.......................................................65
4.3
Average dielectric constant obtained for oil samples at different percentage oils replenishment with adsorbent combination.......................................................66
4.4
Average L*, a*, and b* obtained for oil samples at different percentage oils replenishment with adsorbent combination.......................................................67
XI
CHAPTER 1 INTRODUCTION Fried foods have continued to be popular in spite of the current guidelines which recommend a decrease in the content of fat in our diet (Li, 2005). Frying is a fast and convenient technique for production of foods with unique sensory properties including color, flavor, texture, and palatability that are highly appreciated by consumers. Therefore, it is important to understand the frying mechanism in order to manufacture, preserve, and market fried foods optimally (Moreira et al., 1999). Deep fat frying is a process in which the food is cooked by immersion in hot oil. Despite the fact that the deep fat frying industry is well-established and highly automated, the deep fat frying process is considered to be an art rather than a science (Blumenthal, 1991). It is a complex process. During deep fat frying, thermal, oxidative, and hydrolytic reactions take place resulting in physical and chemical changes in the oil and the formation of new compounds (Li, 2005). Cooking oils are generally treated to separate insoluble material in order to prolong the useful life of the cooking oil. Without any treatment, the cooking oil is generally used for only about 1 to 3 days and must be discarded after such time. According, there is a need to increase the useful life of such cooking oils (Clewell and Friedman, 1976). The useful life of cooking oil can be able to increase by the addition of various adsorbents such as natural adsorbents and synthetic adsorbents. Natural adsorbent include such materials as bentonite, zeolite, activated carbon, diatomaceous earth, active alumina and active magnesia. Synthetic adsorbents have included blends of silicates with magnesium and aluminum oxides, and aluminum oxides with diatomaceous earth (Akoh and Reynolds, 2001). Adsorbents materials or their combinations were found to effectively useful for the control of free fatty acids, polar compounds, dielectric constant and color of used frying oils
1
2 (Mancini-Filho et al., 1986; Yates and Caldwell, 1992, 1993). In addition, the oil replenishment techniques have to be reported to reduce the rate of oil deterioration. It was found that fresh oil replenishment at 15% every 4 h significantly delayed an increase in polymer contents and a decrease in the induction period of frying oil (Chu and Lin, 1996). This study was designed to evaluate the changes in free fatty acid, color, peroxide value, and dielectric constant of the used frying oil because of the addition of adsorbent combinations at different proportions to refresh the oil life. Consequently, to select the best adsorbent combination based on the quality of frying oil; the experiment was conducted to determine the effect of oil turn over rate corporate with the use of adsorbent during filtration for the improvement of frying oil life.
REFERENCES Akoh CC, Reynolds AE. 2001. Recovery of used frying oils. U.S. patent 6,187,355. Blumenthal MM. 1991. A new look at the chemistry and physics of deep-fat frying. Food Tech 45(2): 68-71, 94. Chu YH, Lin JY. 1996. Effect of fresh oil replenishment on soybean oil quality during frying of wheat glutens and chicken nuggets. Food Sci Taiwan 23(4): 544-53. Clewell WS, Friedman B. 1976. Treatment of cooking oil. U.S. patent 3,947,602. Li Y. 2005. Quality changes in chicken nuggets fried in oils with different degrees of hydrogenation. Ph.D. Science, MeGill University, Canada. Mancini-Filho J, Smith LM, Creveling RK, Al-Shaikh HF. 1986. Effects of selected chemical treatments on quality of fats used for deep frying. J Am Oil Chem Soc 63(11): 1452-6. Moreira RG, Castell-Perez EM, Barrufet MA. 1999. Deep-fat frying: Fundamentals and Applications. Maryland: Aspen Publishers, Inc. p. 350. Yates RA, Caldwell JD. 1992. Adsorptive capacity of active filter aids for used cooking oil. J Am Oil Chem Soc 69(9): 894-7. Yates RA, Caldwell JD. 1993. Regeneration of oils used for deep frying: a comparison of active filter aids. J Am Oil Chem Soc 70(5): 507-11.
Chapter 1 Introduction
3
CHAPTER 2 LITERATURE REVIEW Frying of foods is the most common unit operation used in the food preparation and consideration as the important process to develop unique product characteristics with crispy external crust and juicy. Therefore, to produce, preserve, and market of the fried food optimally, it is essential to understand the frying mechanism, and the factors influencing on frying oil degradation during frying process.
2.1
Fundamental of Frying Frying, considered as one of the oldest cooking methods in existence,
originated and developed in the olive growing countries due to the availability of olive oil (Moreira et al., 1999). There are two main methods of commercial frying which are distinguished by the method of heat transfer involved: these are shallow frying and deep fat frying (Fellow, 2000). Today, deep fat fried foods are found in many countries in Europe, Asia, and North and South America (Moreira et al., 1999). Deep fat frying is a very popular and broadly utilized in food preparation because it is fast and convenient. Frying is still considered to be more an art than a science because it is an extraordinarily complex process involving various factors; some of which are dependent on the process itself and others on the food and the types of frying medium used. Deep fat frying involves cooking foods by immersing them in hot oil. Frying oil functions primarily as a heat-conducting medium for the food. This increases the temperature and causes the food to cook. The optimum deep fat frying temperature for coated food ranges from 175oC to 205oC (or 350oF to 400oF). In deep fat frying of foods, the temperature of the heated oil, the frying time, and the fryer type (batch or continuous) are factors that affect the process. The chemical composition of the frying oils, the physical and physicochemical constant,
Chapter 2 Literature review
4 and the presence of additives and contaminants also influence the frying process. Additives or contaminants can have a marked effect on the palatability, digestibility, and metabolic utilization of fried food (Varela et al., 1988). The foods weight/frying oil volume and surface area/volume ratios determine how much fat penetrates the food. The speed and efficiency of the frying process depend on the temperature and quality of the frying oil. The temperature of the oil is usually between 150oC and 190oC. Oil turnover time (mass of used oil/ oil usage rate) is generally about 10 hours. It is important to understand what happens to the temperature and the moisture and oil content of the product during the frying process to determine safe temperature and turnover times of the frying oil for a given fryer type (Moreira et al., 1999).
2.1.1
Frying Oil Characteristics and Oil Deteriorates
The selection of frying oil used in frying process is based on price, quality, flavor, oxidation susceptibility, functionality and availability. The influence of oil composition on oil uptake, type of products, and residues absorbed by deep-fat fried foods is widely documented (Blumenthal, 1991). Oil absorption and degradation of the oil increase with frying time; however, this relationship is not linear. It is found that the oil extracted from the fried food contains higher amount of polymers than the oil remaining in the fryer. Blumenthal (1991) has developed a “frying fat quality curve” of potato crisp, which describes five phases that oil passes through during the degradation process. 1. Break-in oil. When frying begins with fresh oil in a clean fryer, the “breakin” stage, the food products are light in color; raw, ungelatinized starch at the center of the food; no cooked odor; no crisping of the surface; and little oil absorption. During this stage oil has little or no surfactant, so heat is not being transferred efficiently to the food. 2. Fresh oil. The food products are slight browning at the edges of the fries; partially cooked (gelatinized) centers; crisping of the surface; slightly more oil absorption. As food is continuously fried in oil, the degree of surfactant increases, resulting in improved food quality. 3. Optimum oil. The food products produced in an “optimal” stages will have golden brown color; crisp; rigid surface; fully cooked at centers; Chapter 2 Literature review
5 delicious potato and oil odor; optimum level of oil absorption. 4. Degrading oil. As the oil continuously degrades, more surfactants are forms, causing increased contact between the food and oil. This results in darkened and/or spotty surfaces; excess oil pickup; product moving toward limpness; case-hardened surface. 5. Runaway oil. The food products are dark, case-hardened surface; excessively oil products; surface collapsing inward; centers not fully cooked and off-odor and off-flavor. During frying, the breakdown of oil alters the oil quality and composition and forms a variety of small molecular substances affecting the oil quality. Among the compounds produced during oil degradation are surface-active components or surfactants (Stern and Roth, 1959). During frying, the oil is continuously and repeatedly used at elevated temperatures (160-180oC) in the presence of air and moisture. This causes both thermal and oxidative decomposition of the oil. These reactions cause formation of both volatile and nonvolatile decomposition products. They also cause foaming when moist foods are deep fat fried in the oil (Perkins, 1988; Paul and Mittal, 1996). Frying oils are subjected to three different types of environmental conditions, and each environment has its effect on the oil. 1. The storage period starts as soon as the oil is produced and ends when it is placed in the fryer. During this time, the oil is exposed to air at room temperature. 2. The standby period occurs when the oil is heated in the fryer. It includes the time taken to bring the oil up to frying temperature and the time taken for it to cool when frying is finished. During this period, the oil is exposed to air at high temperature. 3. The frying period is that time during which the oil is actually being used for frying. The oil is exposed to air, steam, heat, and the food being fried. The main reactions which can occur are shown in table 1. The rate of formation of decomposition products and really of the products themselves varies with the food being fried, the fat being used, the choice of the fryer design, and the nature of the operating conditions (Stevenson et al., 1984). Also, there is a number of factors that influences deterioration of frying oil; turnover rate, type of the frying process, temperature, intermittent heating and cooling, degree of unsaturation of frying oils, Chapter 2 Literature review
6 type of food material, design and maintenance of fryer, light, and use of filters (Paul and Mittal, 1996).
Table 2.1 Degradation Reactions of Oil Period
Factor
Temperature
Reaction
Speed
Storage
air
ambient
oxidation
slow
Standby
air
hot
oxidation
fast
isomerization
fast
polymerization
slow
pyrolysis
slow
oxidation
fast
Frying
air, water, food
hot
isomerization polymerization pyrolysis hydrolysis
2.1.2
Changes in Frying Oils During Deep Fat Frying
A number of changes take place in frying oils during heating and deep fat frying, involving a complex pattern of thermolytic and oxidative reactions. To obtain the maximum quality of fried products, a good understanding in physical and chemical changes of fats and oils is necessary to further determine the relationship of these compounds to nutritive value, toxic effects of the heated oil, and sensory quality of the oil and food fried in it.
2.1.2.1 Physical Changes in Oils During Deep Fat Frying The physical changes occurring in the oil during frying include darker color, increased viscosity, decreased smoke point, and increased foaming. In fresh frying oil, temperature must be over 204oC before enough volatile material present to visually appear as smoke. As the oxidation and hydrolysis continue, the breakdown products begin to concentrate, and smoke appears at lower and lower temperature (Moreira et al., 1999). When the frying oil is heated and used for a period of time, the
Chapter 2 Literature review
7 oil color darkens due to oxidative reactions. The mechanism for the formation of highly colored compounds is still not fully understood. Melton (1994) proposed that the color changes in fried foods can also dissolve in the oil and will tend to darken the frying oil. The abused oil may thicken and becomes more viscous due to polymerization, oxidation, hydrolysis, and isomerization. Thickening reduces the rate of heat transfer so it takes longer to cook and causes more oil absorption (Moreira et al., 1999). Changes et al. (1978) reported that foods fried in the oil with a foaming tendency are often greasy and less crispy.
2.1.2.2 Chemical Changes in Oils During Deep Fat Frying During deep fat frying, the oil is exposed continuously or repeatedly to elevate temperatures in the presence of air and moisture. A number of chemical reactions occur involving complex thermolytic and oxidative reaction. The reactions consist of hydrolysis, oxidation, and polymerization. As these reactions proceed, the functional, sensory, and nutritional qualities of the oil change and may eventually reach a point where it is no longer able to be used for preparing high quality fried products and it must be discarded.
Hydrolysis The major chemical reaction taking place during commercial deep fat frying is hydrolysis due to large amounts of water introduced from food and the relatively high temperatures at which the oil is maintained. Hydrolysis is the reaction of the water, in the form of steam, released from the food to react with triglyceride and form free fatty acids (FFA), monoglyceride, diglyceride, and glycerol. Newar (1985) reported that excess fatty acids produced in the course of frying are associated with decreases in the smoke point and surface tension of the oil and poor quality of fried food. In addition, FFA continues to breakdown to small molecules that develop off flavors in the fried food.
Oxidation Oxidation is the only reaction that takes place during storage. Oxidation is the reaction of atmospheric oxygen with the oil at its surface. This oxygen attacks the double bonds of the oil structure producing hydroperoxides, the primary oxidative product. Since hydroperoxides are very unstable and flavorless, they further undergo Chapter 2 Literature review
8 three major types of degradation: (1) Fission forms alcohols, aldehydes, acids, and hydrocarbons, thereby also contributing to the darkening of the frying fat and flavor changes. (2) Dehydration forms ketones. (3) Formation of free radicals which form a variety of chemical products such as oxidized monomers, oxidized dimmers, trimers, epoxides, alcohols, and hydrocarbons, which contribute to the increases in viscosity. During the standby and frying period, the oil is still heated in the presence of air, and the process of oxidation becomes rapid. As a result of the breakdown of the double bonds in the oil structure, new compounds are formed in the fryer and have distinctly unpleasant odors. These compounds represent the off tastes and off flavors in the fried products (Moreira et al., 1999). In addition, some metals such as iron and copper can accelerate the oxidation of frying oils.
Pyrolysis Pyrolysis is the formation of lower molecular weight compounds, due to the extensive breakdown of the chemical structure of oil in the frying process (Moreira et al., 1999). One of the compounds forming when oils are overheated of pyrolized is acrolein, a pungent irritant, which can make the working environment quite uncomfortable. Acrolein is formed from glycerol left from hydrolysis of triglyceride.
Polymerization Thermal alteration results in the formation of cyclic monomers, dimers and cyclic compounds through polymerization occurring due to the exposure to high temperature for an extended period of time. The molecules rearrange and the double bonds often end up closer together. Isomerization can make the oil more sensitive to oxidation. Accumulation of these compounds increases viscosity, foaming, and color darkening. Moreira et at. (1999) reported that more than 400 different chemical compounds, including 220 volatile compounds, were identified in the deteriorated oil. Degradation products other than nonpolar fractions are collectively called polar fraction. The polar fraction is subsequently divided into two groups including polymers and composition products. The term of polymer refers to the group of all the degradation products with higher molecular weight than triglyceride. On the other Chapter 2 Literature review
9 hand, the term of decomposition products represents all the group of compounds with lower molecular weight than triglyceride. In general, the major decomposition products formed during frying are volatile decomposition products (VDP) with molecular weight less than 1800 daltons and nonvolatile decomposition products (NVDP) with molecular weight greater than 1800 daltons.
2.1.3
Regeneration of Used Frying Oil
Serious mechanism filtration systems generally have primary and secondary screening mechanisms. Which firstly catch the large particles and secondary enable recirculation (polishing) of the through either a fine mesh stainless steel screen or filter paper. Polishing of the oil increases the effectiveness of the screen as the oil is circulated because the smaller particles are caught in the previously trapped larger particles. Inbuilt or mobile mechanical systems that work this way are much more effective by removing unwanted impurities from the cooking oil than a simple strainer; however, the chemical or soluble contaminants are not removed mechanically and therefore remain in the oil. These dissolved impurities are a major cause of oil breakdown. Filtration is defined as the separation of suspended solids from a liquid by forcing the mixture through a porous barrier filter media. Charred batter and breading particles are a source of decomposition by products and catalyze the degradation of frying oil. Furthermore, it is visually unappealing when the black particulate matter from unfiltered oil sticks to fried food giving it speckled or peppered appearance. Regeneration of used oil has been an area of great importance. In the United State, 1.23 billion pounds of used oil is discarded annually from the restaurant and food services operations (Hunter and Applegate, 1991). The spent oil is generally used in animal feed of for other industrial applications. Recent communications with industrial oil users in Mexico and Southern Europe revealed that these industrials believe oil processors can take used oil and turn it into good oil. In reality, it is never possible to take any kind of used oil, reprocess it, and turn it into a product that it as good as the original. It is, however, possible to treat used oil in a specific manner to retard its degradation, and thereby prolong its useful life and reduce the overall cost of oil. The treatment of used oil needs to be done in a timely manner without undue delay. The treatment produces best results Chapter 2 Literature review
10 when done on-site and preferably on a continuous basis where a small portion of the fryer oil is taken out, treated and fed into the fryer continuously.
Techniques that have been used for oil cleaning and regeneration Various methods have been tried by different academic and industrial researchers to develop a viable system to regenerate spent oil. Some of these techniques have produced good results, while others have demonstrated marginal improvement or even detrimental effects on oil quality. They are: 1.
simple filtration;
2.
filtration using diatomaceous earth;
3.
treatment of used frying oil with adsorbents, comprising activated alumina, magnesium silicates, amorphous silica, etc., and followed by filtration;
4.
steam deodorization;
5.
adsorption, followed by supplementation of tocophorols and/or addition of synthetic anti-oxidants.
The above procedures have been claimed by their authors or inventors as beneficial to the used oil. Simple filtration of used oil from the fryer has been used by many kinds for many years. Type of material is metal strainers or cloth filters have been used to remove the suspended material accumulated in the oil during frying. This process can remove the gross suspended materials, but is not capable of removing either the very small suspended materials or the products of oil breakdown that cause further chemical reaction during frying. Drijiftholt et al. (1990) described a filtration in this process; the oil is filtered through a series of filters with progressively smaller pore size. The oil is filtered under suction through the first filter, and the subsequent filters operate under increasing pressure with the pressure with the pressure in the last filter being less than 5 bar. The inventors claim that the oil degradation is primarily caused by the micro particulate matters accumulated during frying and by filtering them out, one can increase the frying life of the oil. The inventor’s claim appears to overlook the fact that the oil breakdown products can be oil soluble and may not be removed via filtration alone. In addition, the breakdown of oil is not completely driven by the micro particles in the oil. Some Chapter 2 Literature review
11 of the polymeric materials, however, could be coalesced via special techniques and could then be filtered out of the oil. However, this would not totally stop oil breakdown. The invention does not make any reference to this particular aspect. Attempts have been made to add 0.25-0.5% diatomaceous earth into the frying oil, mix it for 5-20 min and then filter the oil. This method removes the suspended materials, including the fine particles. However, it leaves behind practically all of the oil breakdown products.
2.2.
Adsorbent Technology
2.2.1. Sorbents
To be suitable for commercial applications, a sorbent should have (1)
high selectivity to enable sharp separations
(2)
high capacity to minimize the amount of sorbent needed
(3)
favorable kinetic and transport properties for rapid sorption
(4)
chemical and thermal stability, including extremely low solubility in the contacting fluid, to preserve the amount of sorbent and its properties
(5)
hardness and mechanical strength to prevent crushing and erosion
(6)
a free-flowing tendency for ease of filling or emptying vessels
(7)
high resistance to fouling for long life
(8)
no tendency to promote undesirable chemical reactions
(9)
the capacity of being regenerated when used with commercial feedstocks that contain trace quantities of high-molecular-weight species that are strongly sorbed and difficult to desorbs
(10) relatively low cost
2.2.2. Adsorbents
Most solid are able to adsorb species from gases and liquids. However, only a few have a sufficient selectivity and capacity to make them serious candidates for commercial adsorbents. Of considerable importance is a large specific surface area (area per unit volume), which is achieved by adsorbent manufacturing techniques that
Chapter 2 Literature review
12 result in solids with a microporous structure. By the definition of the International Union of Pure and Applied Chemistry (IUPAC), a micropore is <20 Å, a mesopore is 20-500 Å, and a macropore is >500 Å (50nm). Typical commercial adsorbents, which may be granules, sphere, cylindrical pellets, flakes, and/or powders of size ranging form 50 µm to 1.2 cm, have specific surface areas form 300 to 1,200 m2/g. Thus, just a few grams of adsorbent can have a surface area equal to that of a football field (120 x 53.3 yards or 5,350 m2). Such a large area is made possible by particle porosity from 30 to 85 vol% with average pore diameters from 10 to 200 Å. (Seader and Henley, 1998).
2.2.3. Adsorption Mechanisms
Adsorption is sorption operation, in which certain components of a fluid phase, called solutes, are selective transferred to insoluble rigid particles suspended in vessel or packed in a column. Sorption in general term includes selective transfer to the surface and/or into the bulk of a solid or liquid. Thus, absorption of gas species into a liquid and penetration of fluid species into a nonporous membrane are also sorption operations. In a general sorption process, the sorbed solutes are referred to as sorbate, and the sorbing agent is the sorbent (Seader and Henley, 1998). Adsorptions are the process by which molecules of a liquid or gas contact and adhere to a solid surface. Adsorption is always exothermic; heat is liberated. The solid substrate on which adsorption occurs is called the adsorbent, or sorbent. The adsorbing species is the adsorptive, and the adsorbed material is the adsorbate, or simply the sorbate. Adsorbent are very porous materials that contain many miniscule internal pores. The total surface area is enormous 0.1 to 1.0 km2/kg or 20 to 200 football fields per kilogram. Pore sizes are as small as nanometers (Davidson and McMurry, 2000). In an adsorption process, molecules, as shown in figure 2.1, or atoms or ions in a gas or liquid diffuse to the surface of a solid, where they bond with the solid surface or are held there by weak intermolecular forces. The adsorbed solutes are referred to as adsorbate, whereas the solid material is the adsorbent. To achieve a very large surface area for adsorption per unit volume, highly porous solid particles with small-diameter interconnected pores are used (Seader and Henley, 1998). Chapter 2 Literature review
13 Miyaki and Nakajima (2003) used adsorption process for improved the quality of used frying oils and to assess the feasibility of recycle.
Adsorbed layer on surfaces
Adsorbent
Fluid phase in pores
Figure 2.1 Sorption operations with solid-particle sorbents. Adsorption processes are classified as either physical or chemical. The dominant mechanism depends in the adsorbent and the adsorbate(s).
Physical adsorption Physical adsorption occurs when London-van der Waals forces bind the adsorbing molecule to the solid substrate; these intermolecular forces are the same ones that bond molecules to the surface of a liquid. It follows that heats of adsorption are comparable in magnitude to latent heats (10 to 70 KJ/mole). Species that are physically adsorbed to a solid can be released by applying heat (much the same as a liquid can be readily volatilized by heating); the process is reversible. An increase in temperature causes a decrease in adsorption efficiency and capacity. Almost all adsorption processes pertinent to air pollution control involve physical adsorption. Physical adsorption from a gas occurs when the intermolecular attractive forces between molecules of a solid and the gas are greater than those between molecules of the gas itself. In effect, the resulting adsorption is like condensation, which is exothermic and thus is accompanied by a release of heat. The magnitude of the heat of adsorption can be less than or greater the heat of vaporization and changes
Chapter 2 Literature review
14 with the extent of adsorption. Physical adsorption, which may be monomolecular (unimolecular) layer, or may be two, three or more layers thick (multimolecular), occurs rapidly. If unimolecular, it is reversible; if multimolecular, such that capillary pores are filled, hysteresis may occur. The density of the adsorbate is of the order of magnitude of the liquid rather than the vapor state. As physical adsorption takes place, it begins as a monolayer, becomes multilayered, and then, if the pores are close to the size of the molecules, capillary condensation occurs, and the pores fill with adsorbate. Accordingly, the maximum capacity of a porous adsorbent can be more related to the pore volume than to the surface area. However, for gases at temperature, adsorption is confined to a monolayer.
Chemical adsorption Chemical adsorption occurs when covalent or ionic bonds are formed between the adsorbing molecular and the solid substrate. This bonding leads to a change in the chemical form of the adsorbed compounds, and is therefore not reversible. An example of a chemical adsorption process is the formation of CO2 gas adsorbs to a carbon substrate. The bonding forces for chemical adsorption are much greater than for physical adsorption. Thus, more heat is liberated. For many applications the adsorbent is chemically impregnated with a substance that encourages chemical reactions with particular adsorbates. With chemical adsorption, higher temperatures can improve performance (Davidson and McMurry, 2000).
2.2.4. Type of Adsorbents
Absorbent materials for used oil can generally be deviced into three distinct categories, natural inorganic, natural organic and synthetic sorbents.
Natural inorganic sorbents – typically consists of mineral of mineraloid materials, such as clay granules, expanded glass, perlite, and vermiculite mica. They can absorb 1 to 20 times their weight in oil. Inorganic substances are inexpensive and readily available in large quantities.
Natural organic sorbents – typically consists of materials such as peat moss, straw, hay, sawdust, ground corncobs, wood pulp, cotton rags, and other readily available carbon-based products. Organic sorbents can soak up water as well as oil.
Chapter 2 Literature review
15
Synthetic sorbents – typically consists of polypropylene or polyethylene mats, pads, and socks that can be melt-blown, woven or non-woven. Most synthetic sorbents can absorb as much as 20 times their weight in oil, and some types can be cleaned and reused several times. Synthetic sorbents that cannot be cleaned after they are used can present difficulties because arrangements must be made for their temporary storage prior to disposal.
There are several adsorbents commonly used. The most is common is activated carbon, diatomaceous earths, silica, zeolite.
Inorganic Materials
Bentonite Bentonite is specialized clay. As a natural substance it is blessed with numerous special properties, which gives rise to versatile application possibilities. Bentonite consists predominantly of the mineral montmorillonite, and aluminium hydrosilicate structure applied as figure 2.2. Its crystal structure has distinct layers (i.e. a layer lattice). This type of compound is a lamella solid. Between the individual layers, exchangeable cations are inserted. Dependent on the condition under which a bentonite deposit had formed, these cations can be sodium, calcium or magnesium ions. The valency of the included ions is responsible for the swelling capacity, compared to lower bentonite swelling capacity when bivalent calcium or magnesium ions are present. The important properties of bentonite include its ability to exchange cations, its swelling and hydration capacity. Their sorption capabilities com from their high surface area and exchange capacities (Ahmad et al., 2005)
Chapter 2 Literature review
16
Figure 2.2 Structure of bentonite clay. Aluminas Activated alumina is produced form hydrates alumina. Activated alumina is commonly used to remove oxygenates and mercaptants form hydrocarbons and fluorides from water. It is used to support catalysts and as a desiccant. Typical surface areas are 200 to 400 m2/g.
Silicas Silicas are generally clear or faintly tinted, and transparent or translucent. Silica is used to separate hydrocarbons. Typical surface areas are 300 to 900 m2/g. DC chemical Co., Ltd. reported that is used in various fields of our daily life as high adsorbent of high safety. Silica has excellent adsorption capacities at low relative humidity for keeping materials dry. W.R. Grace and Co has reported about silica application; basically used in refining process and bleaching process. For oil that has little or no chlorophyll, silica can be used as a replacement for clay in both caustic and physical refining. Chlorophyll containing oils can be processed by using silica in combination with clay. In addition silica can be remove polar contaminants. Silica offers the greatest potential for the edible oil refining industry (Kent, 2000).
Zeolites Most zeolites are aluminosilicates which could be thought of as stoichiometric blends of the two previous adsorbents, silica and alumina.
Chapter 2 Literature review
17 Thus, they are generally white, opaque and chalk-like in appearance. One would think that given their make-up, all zeolites would be hydrophilic. Accordingly, most that have significant alumina content are hydrophilic, while those that are predominately silica are hydrophobic. Zeolites are generally aluminosilicates. They are crystalline and have micropores that are uniform in dimension. They are called molecular sieves because they can discriminate between nearly identically sized molecules (Kent, 2000 and Davidson and McMurry, 2000).
Diatomaceous earth Diatomaceous earth or diatomite is virtually pure silica which is extracted from the water in which the diatom lives. Thus, they are light colors, porous, and friable sedimentary rock composed of the frustules of diatoms. It is used in industrial filtration application; as a filler or extender in paper, paint, brick and oil filtration. Diatomite, sediment greatly enriched in biogenic silica in the form of the siliceous frustules of diatomite, a divers array of microscopic, single-cell algae of the class Bacillariophyceae. Diatomite products are characterized by an inherently intricate and highly porous structure composed primarily of silica, along with impurities of alumina, iron oxide, and alkaline earth oxides (Sulpizio, 1999).
Organic materials
Activated carbon The most common is activated carbon. While activated carbon can be made form nutshells, wood, and petroleum, most of the activated carbon that is used for pollution control is manufactured form bituminous coal. “Activation” is the process that produces the porous structure essential for effective adsorption. It involves heating in the absence of oxygen to dehydrate and carbonize, followed by heating in the presence of oxygen to obtain the porous structure. Activated carbon attracts non-polar molecules such as hydrocarbons. Typical surface areas are 300 to 1500 m2/g (Davidson and McMurry, 2000). Fortunately, activated carbon offers both low cost and high Chapter 2 Literature review
18 effectiveness and no other adsorbents are close. The choice would be easy, except that there are many activated carbon manufactures, and each of those typically offers several products (Kent, 2000) CPL Carbon Link manufactures a range of Granular Activated Carbon (GAC) and Powdered Activated Carbons (PAC) products for decolorisation applications. Decolorizing applications involve removal of large molecular compounds which require activated carbon with a well developed macropore structure. The information provided here applied to sugar refining but the same concepts and principles apply to other decolorizing application. Activated carbon is non-polar which results in an affinity for non-polar compounds such as organics. These compounds are bound to surface of the activated carbon by adsorption process, which utilizes Van der Waal’s forces. Since adsorption is a surface phenomenon, the adsorption capacity is directly related to the pore structure and surface area of an activated carbon and saturation is only achieved under equilibrium conditions. The equilibrium point is determined by parameters such as temperature, pH, concentration and contact time. Particle size only affects the rate of adsorption and has negligible impact on total surface area, which is determined by the degree of activation and pore structure. It is important to remember that adsorption is not a selective process but will depend on the specific adsorption affinity of each compound which is related to parameters such as molecular size and solubility.
2.3.
Utilization of Adsorbent in Frying Process
Use of other adsorbents, such as activated silica, aluminum oxide, calcium or magnesium oxide, is also quite common. In this case, a certain amount of adsorbent is added into the hot used oil, mixed for some time and then the oil is filtered. This removes the suspended materials; some color bodies and also reduces some free fatty acids. This type of oil treatment, however, has some deleterious effects on the quality of the frying oil. The types of adsorbents mentioned above can be chemically reactive. The alkali, as well as the alkali earth metals present in these adsorbents, can produce soap.
Chapter 2 Literature review
19 The reduction of free fatty acids in the oil could be equated to the amount of soap formed in the oil. The soap thus generated in the oil then promotes rapid oxidation as well as hydrolysis of the oil during subsequent frying. Therefore, the apparent benefit of oil cleaning by this method could be overshadowed by the detrimental effects experienced later in subsequent use of the oil. John Gyann (1988) proposed a blend of amorphous silica, synthetic amorphous magnesium silicate, diatomaceous earth and synthetic silica alumina for rejuvenating spent frying oil. In this invention, the inventor claims that the adsorbent would remove some free fatty acids and other oil breakdown products. It does not clearly specify if the adsorbent also removes the soap that is formed during adsorption due to chemical reaction with metals in the adsorbent and free fatty acids in the oil. Miroil has introduced Frypowder for used oil treatment (Anon, 1992). In their study, the adsorbent was added into the restaurant type fryer to treat the oil in two different ways: 1. Frypowder was added at a certain time interval, the oil was filtered after the treatment and re-used. 2. Oil was filtered at the end of each day. Frypowder was added into the fryer and was not removed until the end of the next day when the oil was filtered and fresh Frypowder was added again. Eddy R. Hair presented steam deodorization as a technique to improve the performance of fryer oil in his International Patent, WO 91/12304. In this process, a small portion of the fryer oil is continuously pulled out of the fryer, deodorized with live stem under vacuum at 148-260oC (300-500oF) and fed back into the fryer. The inventor claims that the oil and product flavor are improved. This is a good technique where removal of free fatty acids is the primary concern. Oil breakdown products can have molecular weights bigger than the largest free fatty acid molecule in the oil. Some of these compounds, such as dimmers and polymers, can have a deleterious effect on product shelf-life, even though steam distillation might have removed free fatty acids and small molecules of volatile compounds. This method can be suitable where extreme precautions are taken in the fryer to minimize oxidative and thermal reactions so that hydrolysis is the main driver for oil breakdown in the fryer. Filtercorp of Woodenville, Washington (Burklund, 1992) has developed a filter pad that is capable of removing trace components from the fryer oil on a Chapter 2 Literature review
20 continuous slip stream treatment process. This prevents the rise of free fatty acids and that of other oxidation products, such as polar compounds, polymers, anisidine value, etc. The alkaline metal concentration is also greatly reduced through this process. The test was conducted on a 500-gallon frying kettle. The typical analyses of the kettle oil before any filtration with the Filtercorp pad are shown in table 2.2. The potato chips, packed in regular bag, would develop rancid flavor within a week at 45oC (113oF). The same oil was filtered through Filtercorp pads. The kettle was operated for 16h per day. A slip stream of oil (60 gpm) was continuously filtered through a 21sq. ft. filter with the Filtercorp pad. At the end of the day, the oil went through a final pass through the filter and stored. The same oil was used the day and was processed through the filter as previously. The test was continued for 2 weeks with 5 working days per week. The oil analyses from the tenth working day are shown in table 2.2. The oil showed a significant improvement in quality. The product made during the test also had superior flavor after 3 weeks of storage at 45oC (113oF).
Table 2.2 Filtercorp oil data after filtration Analysis
Typical kettle oil
After 10 days of
analysis
filtration
<0.05
0.6-2.5
0.5
Alkaline metals (ppm)
ND
25-50
10
Anserine value
6.3
50-100
44.2
Peroxide value
0.2
10-20
9.2
Polymers
2.3
5-12
3.6
Free fatty acids (%)
Fresh oil
In a separate study on a continuous fryer, free fatty acids were measured in the fryer oil. Table 2.3 shows the free fatty acids data after 50 hr of continuous frying. Starting with fresh oil in both cases, the free fatty acids in the unfiltered oil rose to 0.15% after 35 hr, whereas the filtered oil had only 0.08% free fatty acid content. Theses data indicate that the oil breakdown process is greatly reduced when the fryer oil is treated with filtercorp pad from the start of operation.
Chapter 2 Literature review
21 Table 2.3 Free fatty acids in fryer oil with and without filtercorp pad filtration Time (h)
%FFA in filtered oil
%FFA in unfiltered oil
0
0.04
0.04
10
0.07
0.07
20
0.08
0.12
25
0.09
0.13
30
0.08
0.13
35
0.08
0.15
40
0.08
0.15
45
0.08
0.15
50
0.08
0.15
PQ Corporation of Valley Forge, Pennsylvania (Seybold, 1992) reported test results using their silica adsorbent, Britesorb R-100. In their test, French-fried potatoes were made in a restaurant type fryer. The product was fried for 8 hr per day. Fresh oil was added to the fryer after so many batches of product. The oil was treated with 0.70% Britesorb R-100, mixed for 5-10min, filtered, and stored overnight to be used the next day. Oil breakdown products, such as polar compounds, polymers and free fatty acids were measured. In addition, oil color and soap content in the oil were also monitored. Most significant differences between Britesorb R-100 and the other adsorbent were noticed in the soap and polar materials. Results from these tests are listed in table 2.4. The results indicate that Britesorb R-100 is a superior adsorbent compared to other commercially available magnesium and aluminum silicate adsorbents.
Chapter 2 Literature review
22 Table 2.4 Soap and Polar material content of the fryer oil Soap content
Days of operation
Britesorb R100
Polar content
Silicate (mg)
Britesorb R100
Silicate (mg)
1
0
0
6
6
2
0
0
9.5
10
3
0
25
11
12
4
5
90
14.4
17.5
5
9
140
18
22
6
30
200
20.4
27
7
37
290
24
30
8
40
410
26
33
9
45
585
27
36.5
10
50
720
30
40
11
62
825
-
-
During frying process, Fritsch (1981) suggests a series if reactions occur including oxidative, hydrolytic and thermal reactions. Oxidation of oil during frying is caused by direct contact of oil and oxygen at elevated temperature. The reaction is catalyzed by a number of factors such as: 1. the presence of metals in the food being fried or packed by oil from the frying equipment; 2. contamination of the oil by alkali or phosphates left from sanitation; 3. high temperature of frying Hydrolysis of frying oil is caused by reaction with oil and water when they are solubilized in the presence of a surfactant (Sturzenegger and Strum, 1951). The surfactant can come from one or more of the following sources (Gupta, 1992); 1. soap or phospholipids from improperly processed oil; 2. caustic left from fryer sanitation; 3. soaps formed by free fatty acids in oil when the food contains calcium or magnesium salts, typically present in the food coating; 4. oil breakdown products that have surface active properties; 5. soaps, generated in oil due to treatment with magnesium or aluminum
Chapter 2 Literature review
23 silicates of improper physical and chemical attributes. Polymers are formed in the fryer oil when oil is subjected to heat abuse (Nawar, 1985a). This can be associated with one or more of the following factors. 1. incoming oil has been abused by the supplier; 2. oil is stored at high temperature too long before use; 3. fryer is operated for hours at a time without any product in it and the heat is on. Furthermore, one must be able to determine whether or not some preventive steps should be taken in order to minimize oil degradation or even a combination of preventive measure and a fryer oil treatment system be used for optimum results. Preventive measures must be adopted based upon the specific situation. For example: 1. Loose flour and breading material can be removed by mechanical means such as an air-knife or other mechanism before food enters the fryer so that the oil does not get dark prematurely. 2. A proper oil handling procedure can be installed to protect the oil from oxidation before it is used for frying, so that the oil maintains better quality. 3. Take precautions in operation to prevent unnecessary heat or air exposure to oil during frying and subsequent handling of oil. For oil treatment, one must recognize the fact that the best time to treat fryer oil is before it has suffered substantial breakdown. It is advantageous to remove products of oil degradation as they are being formed, as described in the Filtercorp or PQ Corporation studies. The adsorbents, as well as the filter pads, have limited capacity for adsorption of oil breakdown compounds. Adsorbents can become saturated easily when it is attempted to treat seriously abused oil, and the results is always less than satisfactory. Adsorption treatment requires proper filtration of oil. Spent adsorbents, if left in the oil, can catalyze further reaction in oil. A batch filtration system could be adequate for a small size restaurant type fryer. However, for large industrial fryers, this can be expensive. A continuous slip stream filter system could be quite small, relative to the size of the fryer. However, this adds extra volume of oil to the system, increasing oil turnover time. This must be taken into account as part of the total picture. Chapter 2 Literature review
24 Finally, one must recognize that other than simple filtration, all oil treatment operations bring in added equipment, complexity in operation due to unfamiliar technology and added capital cost. All these factors need to be considered carefully before undertaking any oil cleaning step. The user must analyze the operation and determine the source of oil breakdown; then a careful selection of preventive and treatment plans must be developed (Chow and Gupta, 1994).
REFERENCES Anon. 1992. Technical Advertisement. Close the loop, Inform, 3, 1084. Ahmad AL, Sumathi S, Hameed BH. 2005. Residual oil and suspended solid removal using natural adsorbents chitosan, bentonite and activated carbon: A comparative study. J Chem Eng 108: 179-85. Burklund SA. 1992. Filtercorp, Woodenville, WA, personal communication. Chow CK, Gupta MK. 1994. Treatment, oxidation and health aspects of fats and oils: Technological Advances in Improved and Alternative Sources of Lipids. Aspen Publishers, Inc., Maryland, p. 397. Miyaki A, Nakajima M. 2003. Regeneration of Used Frying Oils Using Adsorption Processing. J Am Oil Chem Soc 80: 91-6. Paul S, Mittal GS. 1997. Regulating the Use of Degraded Oil/Fat in Deep-Fat/Oil Food Frying. Cri Rev Food Sci Nutri 37(7): 635-62 Purchas Derek B. 1999. Industrial Filtration of Liquids. Second edition. CRC Cleveland, Ohio, pp. 355-362. Bheemreddy RM, Chinnan MS, Pannu KS, Reynolds AE. 2002. Active Treatment of Frying Oil for Enhanced Fry-Life. J Food Sci 67: 4. Blumenthal MM. 1991. A new look at the chemistry and physical of deep-fat frying. Food Technology. 45(2): 68-71, 94. Change SS, Peterson RJ, Ho CT. 1978. Chemical reaction involved in deep fat frying of foods. J Am Oil Chem Soc 55: 718-22. Fellow, J. 2000. Food Processing Technology. Second edition. Woodhead Publishing Limited, Washington, pp. 355-62. Fritsch CW. 1981. Measurement of frying fat deterioration. J Am Oil Chem Soc 58: 172.
Chapter 2 Literature review
25 Gupta MK. 1992. Designing frying fat, AM. Oil Chem. Soc. World Conference, Budapest, Hungary. Hunter JE, Applegate TH. 1991. Reassessment of trans fatty acids availability in U.S. diet. Am. J. Clin. Nutr. 54: 363. Kent S, Knaebel. 2000. Adsorbent Selection. Adsorption Research, Inc. Ohio, USA. Melton SL, Jafar,S, Sykes D, Trigiano MK. 1994. Review of stability measurements for frying oils and fried food flavor. J Am Oil Chem Soc 71: 1301-8. Moreira RG, Castell-Perez EM., Barrufet MA. 1999. Deep-fat frying: Fundamentals and Applications. Aspen Publishers, Inc., Maryland, p. 350. Newar WW. 1985a. Chemistry of thermal oxidation of lipids, in Flavor Chemistry of Fats and Oils. Am Oil Chem. Soc., Champaign, IL. Newar WW. 1985. Lipids. In “Food Chemistry,” ed. O.R. Fennema, Marcel Dekker, New York, pp. 175-89. Paul S, Mittal GS. 1996. Regulating the used of degraded oil/fat in deep fat/oil food frying. Cri. Rev. Food Sci. Nutri. 37(7): 636-2. Perkins EG. 1988. The analysis of frying fats and oil. J Am Oil Chem Soc 65(4): 520-5. Seader JD, Henley EJ. 1998. Separation process principles. John Wiley and Sons, Inc. New York, p 886. Seybold JE. 1992. P.Q. Corp., Valley Forge, PA, personal communication. Stern S, Roth H. 1959. Properties of doughnut frying fat. Cereal Sci. Today. 4(6): 176-9. Stevenson SG, Jeffery J, Vaisey-Genser M, Fyfe B, Hougen FW, Eskin NAM. 1984. Performance of canola and soybean fats in extended frying. Can Inst Food Sci Technol J 17: 187-90. Sturzenegger A, Strum H. 1951. Hydrolysis of fat at high temperature. Int Eng. Chem. 43: 510. Sulpizio TE. 1999. Advances in filter aid and precoat filtration technology. Presentation at the American Filtration & Separation Society. Annual Technical Conference, Boston, Massachusetts. Varela OM, Roso BR, Varela G. 1988. Effects of frying on the nutritive value of food. In “Frying of Food: Principles, Changes, New Approaches” Chichester, Ellis Horwood, pp. 93-102.
Chapter 2 Literature review
CHAPTER 3 UTILIZATION OF MIXED ADSORBENTS TO EXTEND FRYING OIL LIFE CYCLE ABSTRACT The used frying oil in the fried poultry processing were tremendously prolonged and improved in oil life cycle using the adsorbent technology by decreasing the physico-chemical changes such as color, and the rate of oil deterioration (indicated by %FFA, PV and FOS Reading). The frying oil treated with com I (bentonite: activated carbon: celite; 3:4:1) remarkably reduced %FFA, PV, and FOS readings by 44.31%, 50.20%, and 40.12%, respectively, while the oil treated with com II (bentonite: activated clay: celite; 3:4:1 mixed with citric acid 1% w/w) could decrease by 41.61%, 44.86%, and 32.83%, respectively. In addition, the oils added with com I and com II increased color parameters indexes L*, a*, and b* were 30.70%, 53.19%, and 1.69%, 19.11%, and 31.68%, 39.53%, respectively. The higher L* observed, the more oil quality obtained because of the bleaching ability of adsorbent. The future feasibility to use mix adsorbent corporate with filtration system and oil turn over rate for improved in frying oil life was reported.
Keywords: adsorbent, frying oil, FFA, PV, FOS readings
26
27
INTRODUCTION The quality of oil used in deep fat frying directly contributes to the quality of the fried food. It is necessary to maintain the quality of oil in frying system as good as possible because the undesirable constituents produced from degraded oils may even be harmful to health. In general, approximately 50% (or more) of frying fat and oil used in food service operations is discarded after frying (Hunter and Applewhite, 1993). However, some amounts of used oils are still remained in fryer and adsorbed by every single fried product. Many scientific studies have been addressed the safety of the used oils and claimed that the regular cleaning and maintenance of equipment, good quality frying fat, and utilization of proper frying conditions are essential in order to reduce these detrimental effects and to prolong the useful life of frying oil (Stevenson et al., 1984). Currently, the use of various natural and synthetic adsorbents for removing oil soluble degraded compounds is intensively interested. Several materials have been proposed to capably adsorb the polar degradation products of the used oils for example, activated carbon, synthetic magnesium oxide, diatomaceous earth, bleaching earth, synthetic calcium silicate calcium, and various forms of silica. Jacobson (1967) reported that synthetic calcium silicate and synthetic magnesium silicate were able to reduce FFA and color, respectively. There existed a study about the effects of bleaching clay, charcoal, celite, and their mixture on the extension of frying oil life. It found that the DCC remarkably improved with regarding the utilization of bleaching clay and charcoal, and the color of used oil (measured at absorbance 420 nm) effectively reduced by all treatments (Mancini-Filho et al., 1986). Yates and Caldwell (1993) had been purposed to adsorb the polar degradation products of regenerating used frying oils. Among them were diatomaceous earth, acid activated bleaching clay, activated aluminas, silica, activated carbon and synthetic magnesium silicate. Significant differences in the adsorbents characteristics of the materials were investigated (Hunt, 1976; Barder et al., 1989; Mobbs et al., 1993; Roy 1994). McNeill et al. (1986) also examined on the feasibility of various mixtures between activated carbon and silica for improving the quality of used canola oil and reported that the canola oil treated with mixed adsorbents showed more effective Chapter 3 Utilization of mixed adsorbents to extend frying oil life cycle
28 reduction in acid values, peroxide value, saturated and unsaturated carbonyl contents, polar compounds and photometric color than the control. Activated carbon seemed to more decrease saturated and unsaturated carbonyl content in oil samples than silica. Several studies have been proved that the use of mixed adsorbents were more advantageous than the single usage due to greater capability and higher adsorption power to react the chemical compounds in the used oils. The use of filter aid is a practical and efficient method which the frying industry employs to extend use life of frying oils and improve healthy aspects of used frying oils. Researchers have shown interest in using commercial synthetic adsorbents such as Britesorb, Hubersorb600, Frypowder and Magnesol to maintain oil quality and recover used oils. A mixture of them attempted to reduce FFA by 82.6-87.6%, absorbance at 420 nm by 26.8-32.6%, and FOS reading by 5.6-8.6% (Lin et al., 1999). In addition, the improvement of the recovered used oil after 32 hr, the quality parameters of FFA, TPC, FOS reading and color difference were reduced by 64.2, 19.1, 32.6 and 4.4%, respectively (Lin et al., 2001). However, several studies have been reported on adsorbents and their properties; however these do not provide insight to their performance under practical conditions on a commercial scale (Boki et al., 1989; Yates and Caldwell, 1992; Zhu et el., 1994). The objective of this study was to investigate the performance of adsorbent combination for improving frying oil quality and prolonging frying oil life in commercial frying scale.
MATERIALS AND METHOD Materials
Food raw materials Commercial breaded chicken drumsticks obtained from BETTER FOODS Co., Ltd. were used in this study. Fresh and clean chicken drumsticks were soaked in 15% seasoning solution containing salt, pepper, MSG, and STPP (BETTER FOODS Co. Ltd., Thailand) and subsequently predusted, steamed, battered and then individually powdered about 140g of wheat flour, modified corn starch, water, salt, spices, sugar,
Chapter 3 Utilization of mixed adsorbents to extend frying oil life cycle
29 artificial flavor, paprika powder, and extracts of paprika in soy bean oil. The drumsticks were nearly uniform in shape and size (about 10 cm x 13 cm x 3 cm) and weighed approximately 140 g/piece. The temperature of the breaded drumsticks was at 45oC before frying. The initial moisture and fat content of the breaded drumsticks were 62.54% and 45.06%, respectively.
Frying oil Partial hydrogenated soybean oil was obtained from a local processor (Argkun, Cheer Co., Ltd., Thailand) and supplied in 13.75 liters of tin can. The quality of fresh oil was batch measured to keep the data for manufacture.
Adsorbents Five different adsorbents including celite (Celite® coarse 545, Fluka chemical, Buchs, Switzerland), activated clay (Power Dry Co., Ltd., Thailand), activated charcoal (Fluka chemical, Buchs, Switzerland), bentonite (Sigma Aldrich Chemica, GmbH, Germany), and citric acids were used to examine on the adsorption capability for the degradative polar constituents in the used oils. Celite was a white powder, odorless powder composed of silicon dioxide (SiO2); activated clay was gray granules, odorless, insoluble in water composed of calcium alumino silicate; activated charcoal was a black powder, odorless; bentonite was light brown in color, odorless powder composed of silicon dioxide (SiO2), aluminum dioxide (Al2O3). Two different adsorbent combinations used in this experiment were Com I (consisting of bentonite, activated charcoal, and celite at ratio of 3:4:1), and Com II (3:4:1 of bentonite, activated clay, and celite + 1% of citric acid). The selection of the types of adsorbent and their appropriate ratio was based on our preliminary study.
Frying Experiments
The frying treatments was composed of three different treatments and labeled as ‘control’, ‘Com I’, and ‘Com II’. The frying treatment labeled ‘control” contained oil without adding adsorbents but filtering with a regularly commercial filter paper pore size is 30 µ to remove the food crumbs and particulates at the end of each frying day. On the other hand, the treatments labeled as ‘Com I’ and ‘Com II’ contained oils Chapter 3 Utilization of mixed adsorbents to extend frying oil life cycle
30 with adding the different mixed adsorbents and using filtration system. These were to evaluate the efficiency of the selected adsorbent combinations for prolonging the useful life of frying oil. Each frying treatment was conducted for 6 day long attempting to simulate the commercial industrial frying. Fryer was switched on for 6 hr per day. Thirty six batches of powdered chicken drumsticks were continuously fried per day to mimic the same amount of frying load/oil used in this manufacturing. Each batch consisting of four powered chicken drumsticks was fried at 10 min intervals.
Frying test
The powdered drumsticks were fried in a commercial dual-unit electric batch fryer Model H 114-2 CSC (Fry-master, Shreveport, LA, USA) with a capacity of 21 liters of frying oils. The model of fryer is shown in figure 3.1. Before frying, fresh oil was preheated at 175oC for 30 min to simulate to normal frying condition. The frying oil was maintained at +5oC of the set temperature (175oC) using a programmable temperature controller. In addition, no fresh oil was added during frying. However, in the beginning of the next frying date, the small amount of fresh oil about 200 ml per day might be added in the fryer to keep the initial oil level constantly. Four powered chicken drumsticks about 560g were randomly fried in 13 kgs of heated oil. Each batch of the chicken drumsticks was fried at a temperature of 175oC. For each frying cycle, the chicken samples were fried for 150 sec and then the temperature of frying oil was kept at 175oC for the rest of frying cycle even if unloading food materials. The gap timing between each frying cycle provided time for the next batch preparation and permitted the fryer to make up any loss in temperature. The chicken samples were placed in a stainless basket to keep them submerged. The fried samples were immediately withdrawn from oil and cooled to the ambient temperature.
Chapter 3 Utilization of mixed adsorbents to extend frying oil life cycle
31
Electric fryer
Portable filtration
Figure 3.1 Electric fryer and portable filtration Oil filtration
At the end of each day, after the last batch of frying, gravity filtration method was used to filter the used oil. The hot oil from the fryer pot was collected into an oil container and then recirculated and filtrated under vacuum condition with filter paper as recognized as the control. The filter paper obtained from (Noonsfeer Co., Ltd., Thailand). The oil from the fryer pot was filtered in order to remove the food crumbs and batter sediments. Similarly, oils in ‘Com I’ and ‘Com II’ treatments were gravity filtered, treated with 1% (by weight) adsorbents, and then recirculated for passing through the filter paper. After continuously poured and stirred to the recirculated oil for 5 min, the adsorbent particles were ultimately recovered and separated from the used oil via vacuum filtration system for 20 min. The model of portable mobile filtration system is shown at figure 3.1.
Oil sample collection
The frying oil was randomly collected every 3 hr, twice a day. The oil samples were individually kept in closed container, sealed off with the cap in order to prevent the oxidation, then air cooled in dark room (approximately 7oC) for 1 hr after that keep at room temperature until the further physico-chemical analyses. The FFA, PV, FOS reading, and color parameters were measured with regard to express the
Chapter 3 Utilization of mixed adsorbents to extend frying oil life cycle
32 deterioration rate of the oil.
Analysis tests of oil quality
Free Fatty Acid (FFA) Composition of free fatty acids was analyzed using AOCS procedure Ca 5a40. The designated quality of sample was weighted into Erlenmeyer flask. Next the specified amount of hot, neutralized alcohol 95% and 2ml phenolphthalein indicator was added into the flask. Finally the sample was titrated with 0.1N alkali, shaked vigorously until the appearance of the first permanent pink color of the same intensity as that of the neutralized alcohol before addition of the sample. The color must persist for 30 seconds (AOCS, 1990). The test was duplicated.
Peroxide value (PV) Peroxide value was determined by AOCS procedure Cd 8-53 (AOCS, 1990). The test was duplicated.
Dielectric Constant The dielectric property of all samples was measured by Food Oil Sensor (model NI-2C, Northern Instrument Co., Lino Lakes, MN). In general, the test consisted of two steps. In first step, the instrument was equilibrium balanced to a zero state with the fresh oil used in the frying process. A few of the fresh oil or test oil drops onto open test cell, containing a heater and temperature controller. The dielectric properties of oil normally varied due to the different in oil source and the oil temperature, it is essential that all readings must be taken at the same temperature. The awareness of the difference in fresh and tested oil samples was essential concern and the temperature of both oils required the same. After, calibrated using fresh oil to zero, the fresh oil was then removed from the instrument cup with soft tissue paper; suddenly the tested oil samples were added in the cup to measure the change in dielectric constant. The test was performed in duplicated.
Color The equipment used for determining oil color was a Tintometer (model PFX190, Lovibond, England). Color of frying oils was measured at the L*, a*, and b*. Three Chapter 3 Utilization of mixed adsorbents to extend frying oil life cycle
33 color readings were taken from each oil sample and the average was used for analysis.
Statistical methods
Statistic analyses were performed using General Linear Model Program (GLM) to test the capability of the adsorbent combinations for improving frying oil quality and prolonging frying oil life in commercial frying scale. Least Significant Difference (LSD) was used to estimate the significant differences among the means of each treatment at 5% the probability level using SAS program (SAS, 2000).
RESULTS AND DISCUSSION Assessment of oil quality
The used frying oils used in this experiment were collected from the fryer fried only powdered chicken drumsticks and the frying system was nearly similar to the operating situation normally existing in the factory. In addition, no fresh oil was added during frying. The effects of adsorbents combinations (com I and com II) on the changes in free fatty acid content, peroxide value, FOS reading, and color parameters of used oil recovery were conducted. A typical graph expected from these test results was reported where, the x-axis represented the frying time in hour (hr) and the y-axis represents the oil quality parameters such as color, FFA, PV, and FOS readings. All quality parameters in terms of color, FFA, PV and FOS reading of the oil treated with com I and com II successfully decreased (p≤0.05).
The formation of FFA content
When the oil samples were analyzed, the FFA content of the oil would be the lowest at the beginning of the day and gradually increased with frying time for that particular day. This information would confirm why most frying manufactures normally used FFA as the traditional method for monitoring the oil quality. The FFA of both treated oils with com I and com II were significantly lower than the control
Chapter 3 Utilization of mixed adsorbents to extend frying oil life cycle
34 (fig. 3.2). In general, free fatty acids were form in large quantities as a result of hydrolysis, oxidation due to free radical formation and due to cleavage of double bonds during frying. Some researchers consider free fatty acids as good measure of frying oil quality. The other do not consider FFA as good indicator of frying oil quality which may be due to the fact that free fatty acids further react to form volatile compounds and polymers. In the present study, FFA test was selected as it was reported to be sensitive in differentiating adsorbent treatments (Bheemreddy et al., 2002). The FFA of the control started from 0.33% and reached 0.55% after 18 hr operation. This trend was nearly the same that suggests by Lin et al. (2001). After 36 hr of continuous frying, FFA of the control oil was nearly 1.0%. Regarding to the regulation, most meat-frying operators traditionally made decision to discard the used oil at 2.0% of FFA. However, this could vary because it also depended on the ingredients used in food materials. Use of spices may result in discard point less than 2%. It was noticeable that the increments of FFA during the same each frying day (at 6, 12, 18, 24, 30 hr) attained the similarity of slopes and then FFA content would be steep at the end of the frying day (fig. 3.2). This indicated that the use of filtration and adsorbent addition potentially improved quality oil or retarded the rate of deterioration. In addition, at the end of each day treated oils in both com I and com II systems remarkably exhibited the achievements to significantly (p≤0.05) reduce FFA content when compared to the control. It implies that the daily application of active adsorbent in oil treatment showed the less accumulation of FFA in treated oil than in the control. As expected, activated carbon mixed in the combination could remove impurities by occlusion and adsorption based on its chemical properties. In addition, celite was type of diatomaceous earth in form of silica oxide that normally recognized to able adsorptive qualities due to base primarily on interaction with exposed silanol group. According to McNeill et al. (1986), the carbon and silica mixture were most effective in reducing acid value. That result related to reported by Mancini-Filho et al. (1986), which had suggestion that celite acted principally as a filter aids for treatment by the mixtures of adsorbents. At the end of frying 36 hr, FFA contents in com I and com II systems were closely 0.45% and 0.49%, respectively. The effectiveness to improve the used oil Chapter 3 Utilization of mixed adsorbents to extend frying oil life cycle
35 quality between two combinations was not significantly (p≥0.05) but excellent when compare to the control. The FFA improvement ability in com I and com II was presented in table 3.7 by 44.31%, 41.61%, respectively.
The changes in PV
The analytical measure of oxidative deterioration of oils and fats is the peroxide values. Peroxide value is a measure of the amount of peroxides forms in fats and oils through autoxidation and oxidation process. Indirectly, it is a measure of the degree of initial oxidation of fats and oils (Che Man and Jaswir, 2000). Table 3.2 showed that com I and com II could significantly (p≤0.05) reduce the oil oxidation process during frying while compared with the control. The results were not far from that suggested by Mancini-Filho et al (1986). The reduction in peroxide value was approximately the same regardless of the levels of com I and Com II at 36 hr. From 6 hr, peroxide values of the control had stronger tendency (fig.3.3) to augment when compared with com I and com II. As expected, the addition of mixed adsorbents into the used oil had a significant (p≤0.05) decrease in peroxide values. According to Omar et al., (2003), bentonite was one of the powerful chemical compounds to effectively adsorb the chemical constituents affecting peroxide value. Normally, bentonite is used in bleaching step. During bleaching of vegetable oils, peroxide compounds are degraded and then removed. As well as FFA formation, peroxide value of the control oil significantly elevated and climbed up to three times. In contrast, both treated oil with added absorbents still maintained the level of PV. As usual, PV from all treatment was fluctuated since peroxide compounds were less stable and might change to another in secondary oxidative products such as aldehydes, hydrocarbons, and ketones in final oxidation step. The results were related to Hammond (2000), reported about peroxides were not stable above 50oC. Even though, there was the use of filtration and adsorbent to treat the oil, this operation normally took under high temperature of oil about 150-175oC. That resulted in the change of a mount of peroxides compounds. The treated oils with com I and com II were capable to improve the reduction of peroxide value by 50.20%, 44.86%, respectively (table 3.7).
Chapter 3 Utilization of mixed adsorbents to extend frying oil life cycle
36 The efficiency to reduce FOS readings
Food oil sensor (FOS) reading is one of the quick tests used to determine the quality of used frying oil. It measures the changes in dielectric properties of used oil. Fritsch and others (1979) reported that oxidation products were primary responsible for the change in dielectric properties of oil. El-Shami and others (1992) also reported that the changes in dielectric properties were directly proportional to the amount of total polar compounds in the oil. Total polar compounds (TPC) were considered the most reliable method for evaluating frying oils. However, estimation of TPC was very need to consuming and required a skilled person to do test. Hence FOS reading was considered a convenient indicator of quality control of frying oil. FOS readings of the all treated oils increased (p≤0.05) with frying time. The graphic pattern of FOS looked the same as the inclement of FFA content. After 12 hr of frying, the treated oil with two different adsorbent combinations gradually elevated and reached 2.22 for com I and 2.69 for com II. Both presented the successful achievement to prolong the useful life of oil. In contrast, the FOS readings of the control oil were considerably higher than the others without the addition of adsorbent. It was indicated that the total polar compound components more formed in the control oil than in the treated oils. As concluded, the oil treated with adsorbent showed the significant improvement (table 3.3) which confirmed the report of Lin et al., (1999 and 2001), Mancini-Filho et al. (1986), McNeill et al. (1986), and Bheemreddy et al. (2002).
The changes in oil color
Color is one of the traditional methods used for assessing oil quality. Color development is an indication of oxidation, polymerization, and formation of carbonyl compounds. The color of the frying oil darkens with use and eventually affects the color of fried product. Many researchers have reported color as an important parameters indicating overall quality of oil (Bheemreddy et al., 2002). However, some of the researchers also think that it is not a reliable indicator of oil quality because oil color is influenced by factors like type, amount of food being fried, and food oil interactions leading to reactions such as Maillard browning. Thus, used of oil color or monitor quality is not valid evaluating a wide range of frying operations. Chapter 3 Utilization of mixed adsorbents to extend frying oil life cycle
37 However in this experiment both the treatments were treated very similar with the same frying medium, type, and amount of food fried. Therefore, use of color for monitoring oil quality in this experimental was justified. Moreover, one of the benefits of active treatments was improvement in color. Hence, it was important to measure color to judge the efficiency of active treatment. The color data presented in the graphs (fig. 3.5) were average values. The oils treated with adsorbents were significantly lighter, less yellow, but redder than the control. It was important point of view that the good oil used in the frying operations might be able to maintain the original color like the fresh oil due to easily control the color of products fried in it. However, in this experiment, the fried products consisted of some ingredients such as paprika powder, and extracts of paprika, it made the oil redder with longer frying time and susceptibly degraded that oil. Yellow color represented by the b value reported that the treated oil samples were consistently less yellow in color than in the control and shown inverse values to redness. These values may not be considered very reliable to indicate the state of deterioration of frying oils. On the other hand, red values were a value which represented the degree of redness increased very fast at the beginning of frying for all treatment. That result related to suggestion of Lin et al. (2001), whereas a slight elevation was observed during the first 6 hr for all samples presented in figure 3.5. After about 27 hr of refrying, the a* of both treated used oil reached maximal value. In the final at 36 hr for control, com I, and com II were -4.75, -4.67, and -3.84, respectively, which indicated for 1.69% of com I, and 19.11% of com II. The improvement ability to reduce in color due to active treatment was reported in table 3.7.
Effect of Adsorbent Combination on Recovery of Used Frying Oil Quality
Both adsorbent combinations were individually determined their efficiency and effectiveness to recover the oil quality and prolong the oil life. As expected, the deteriorative rate of used oil considerably decreased as measured via both physical and chemical changes after treated oil with two different adsorbent combinations. The adsorbent combinations comprising activated carbon + bentonite + celite for com I, and activated clay + bentonite + celite + citric acid for com II were selected to be the most effective on recovery of used frying oil with respect to the preliminary Chapter 3 Utilization of mixed adsorbents to extend frying oil life cycle
38 study. Generally, the acidity of all oils was remarkably reduced by treatment with adsorbent combinations as shown in the reduction in FFA content and FOS readings. Normally in the control system, frying oil was severely abused with high temperature and finally exhibited 0.81% of FFA content (table 3.1). However, the FFA contents of the oil treated with com I and com II attempted to reduce by 44.94%, and 39.51%, respectively as compared to the FFA in the control. In term of color parameters, the lighter the color, the better the oil was recovered. For the L* in com I, com II increased from 30.70%, and 53.19%. Regularly, the L* of the control without addition of adsorbent was greater than one in the treated oils due to unable stand to high heat during frying. In addition, the selected adsorbents used in these formulations had powerfully ability to remove the charcoal or other color constituents formed in the oil so that the oil would become lighter in color. The improvement ability in oil color was expressed in table 3.7. As expected, the oil treated with com I exhibited better performance in oil quality improvement than com II due to lower all oil quality indexes (FFA content, PV and FOS reading) but less powerful to bleach the used oil color with regarding to obtained darker, less yellow and red in color than com II. This may be the use of activated clay in com II and there existed some charcoal residues dispersing in the com I system. At the end of 36 hr frying, the improvement abilities for FFA, PV, and FOS reading of com I and com II were 44.31%, 50.20%, 40.12%, and 41.61%, 44.86%, 32.83%, respectively. In case of physical properties for the L*, a*, and b*, the improvement ability of com I and com II were 30.70%, 1.69%, 31.68% and 53.19%, 19.11%, 39.53%, respectively (table 3.7). In untreated oil, after at the end of the day the oils were passing to the paper filtration without filter aid. Filtration could remove insoluble impurities generated in frying oil but cannot remove soluble deterioration products, including FFA, polar materials, and color compounds (Lin et al., 2001). Filtration and adsorbents addition improved the oil quality to some degree, and slowed the deterioration (fig. 3.2-3.5). At the end of each day, the FFA values, PV, FOS reading, and color parameters were improved due to the effect of removal of food debris. The daily treatment with adsorbent com I and com II, not only remove more FFA each time of treatment, but it also controlled the FFA build-up at very low
Chapter 3 Utilization of mixed adsorbents to extend frying oil life cycle
39 rate, and kept the level of FFA below 0.45%, and 0.49%, respectively at the end of 36 hr frying (table 3.1).
CONCLUSIONS Treatment of used frying oils with adsorbent combinations could significantly (p≤0.05) improve the quality of frying oil either by extension of frying life of the recovered used oil or by slowing down the rate of deterioration of fresh oil, while compare with control. At the end of 36 hr refrying with treated oils, com I and com II, the FFA value, PV value, FOS reading, and color parameters; L*, a* and b* reduced by 44.31 and 41.61%, 50.20 and 44.86%, 40.12 and 32.83%, 30.70 and 53.19%, 1.69 and 19.11%, and 31.68 and 39.53% of the values for treated oil, respectively. Such adsorbent combinations may be useful to enhance the quality of fried food and prolong oil life. For both in treated adsorbent combination, which improvement ability is different for the chemical properties com I is better than com II, physical properties com II better than com I in case of L*, a*, and b*. Therefore, such optimized com II could be used in next experimental with oil replenishment to extend the life of frying oils. Because of the chemical parameters did not significantly (p≤0.05) different on both treated, including FOS readings, a*, and b* at 36 hr (table 3.1-3.5), for the L* value had significant (p≤0.05) improvement.
REFERENCES Akoh CC, Reynolds AE. 2001. Recovery of used frying oils. U.S. patent 6,187,355 B1. AOAC Assoc. Official Analytical Chemists. 1995. The official methods of analysis. 16th ed., vol. 2, Arlington, Va.: AOAC. Bheemreddy RM, Chinnan MS, Pannu KS, Reynolds AE. 2002. Active treatment of frying oil for enhanced fry-life. J Am Oil Chem Soc 67(4):1478-84. Boki K, Shinoda S, Ohno S. 1989. Effects of filtering through bleaching media on decrease of peroxide value of autoxidized soybean oil. J Food Sci 54 (6): 1601-3. Che Man YB, Jaswir I. 2000. Effect of rosemary and sage extracts on frying
Chapter 3 Utilization of mixed adsorbents to extend frying oil life cycle
40 performance of refined, bleached and deodorized (RBD) palm olein during deep-fat frying. Food Chem 69: 301-7. Hammond EW. 2000. Oil quality management and measurement during crisp/snack frying in palmolein. OFIC 2000 Conference, Kuala Lumpur. Jacobson GA. 1976. Quality control of commercial deep fat frying. Food Tech 21: 43-8. Lin S, Akoh CC, Reynolds AE. 1999. Determination of optimal conditions for selected adsorbent combinations to recover used frying oils. J Am Oil Chem Soc 76(6): 739-44. Lin S, Akoh CC, Reynolds AE. 2001. Recovery of used frying oils with adsorbent combinations: refrying and frequent oil replenishment. Food Res Int 34: 15966. Mancini-Filho J, Smith LM, Creveling RK, Al-Shaikh HF. 1986. Effects of selected chemical treatments on quality of fat used for deep frying. J Am Oil Chem Soc 63(11): 1452-6. McNeill J, Kakuda Y, Kamel B. 1986. Improving the quality of Used Frying oils by treatment with activated carbon and silica. J Am Oil Chem Soc 63(12): 15647. Omar S, Girgis B, Taha F. 2003. Carbonaceous materials from seed hulls for bleaching of vegetable oils. Food Res Int 36: 11-7. Paul S, Mittal GS. 1997. Regenerating the sued of degraded oil/fat in deep-fat/ oil food frying. Critical rev in Food Sci Nutri 37(7): 635-62. Seybold JC. 1995. Method of frying oil treatment using an alumina and amorphous silicon composition. U.S. patent 5,391,385. Stevenson SG, Vaisey-Genser M, Eskin NAM. 1984. Quality control in the used of deep frying oils. J Am Oil Chem Soc 61(6): 1102-8. Varela G. 1988. Current facts about the frying of food. In G. Bender AE, Bender, and I.D. Morton, Frying of food: principles, changes, new approach (pp. 93102). Ellis Horwood, Chichester, UK Yates RA, Caldwell JD. 1992. Adsorptive capacity of active filter aids for used cooking oil. J Am Oil Chem Soc 69(9): 894-7. Yates RA, Caldwell JD. 1993. Regeneration of oils used for deep frying: A comparison of active filter aids. J Am Oil Chem Soc 70(5): 507-51. Zhu ZY, Yates RA, Caldwell JD. 1994. The determination of active filter aid Chapter 3 Utilization of mixed adsorbents to extend frying oil life cycle
41 adsorption sites by temperature-programmed desorption. J Am Oil Chem Soc 71(2): 189-94.
Chapter 3 Utilization of mixed adsorbents to extend frying oil life cycle
42
Free Fatty Acid (%)
0.8 0.7 0.6 0.5 0.4 0.3 0
3
6
9
12
15
18
21
24
27
30
33
Time (h) Control
Com I
Com II
Figure 3.2 The changes of free fatty acid in untreated and treated used oil during frying 36 hr
Chapter 3 Utilization of mixed adsorbents to extend frying oil life cycle
36
43
13.5 12.5
Peroxide Value
11.5 10.5 9.5 8.5 7.5 6.5 5.5 4.5 3.5 2.5 0
3
6
9
12
15
18
21
24
27
30
33
Time (h)
Control
Com I
Com II
Figure 3.3 The changes of peroxide value in untreated and treated used oil during frying 36 hr
Chapter 3 Utilization of mixed adsorbents to extend frying oil life cycle
36
FOS Reading
44 4.4 4.2 4.0 3.8 3.6 3.4 3.2 3.0 2.8 2.6 2.4 2.2 2.0 1.8 0
3
6
9
12
15
18
21
24
27
30
33
36
Time (h) Control
Com I
Com II
Figure 3.4 The changes of dielectric constant in untreated and treated used oil during frying 36 hr
Chapter 3 Utilization of mixed adsorbents to extend frying oil life cycle
Lightness (L*)
45 98 96 94 92 90 88 86 84 82 80 78 76 74 72 70 68 66 64 62 60 58 56
-2.0 -2.5
Redness (a*)
-3.0 -3.5 -4.0 -4.5 -5.0 -5.5 -6.0 -6.5
Yellowness (b*)
-7.0 38.0 36.0 34.0 32.0 30.0 28.0 26.0 24.0 22.0 20.0 18.0 16.0 14.0 12.0 10.0 8.0 6.0 4.0 0
3
6
9
12
15
18
21
24
27
30
33
36
Time (h) Control
Com I
Com II
Figure 3.5 The changes of quality parameters during 36 hr of refrying with untreated oil and treated oil, where color parameters in Tintometer coordinates L*, a*, and b*.
Chapter 3 Utilization of mixed adsorbents to extend frying oil life cycle
46 Table 3.1 Changes in overall free fatty acid in untreated and treated used oil during frying 36 hr Control a
Time (hr)
Com I b
Com II c
0
0.34 aI
(0.02)
0.31 aD
(0.03)
0.31 aF
(0.02)
3
0.37 aIH
(0.05)
0.36 aBDC (0.05)
0.35 aF
(0.01)
6
0.49 aFEHDG (0.10)
0.41 aBAC (0.08)
0.40 aDC (0.01)
6
0.38 aIH
(0.03)
0.34 aDC
(0.03)
0.36 aE (0.01)
9
0.46 aFHG
(0.01)
0.36 bBDC (0.02)
0.38 bDE (0.03)
12
0.51 aFCEDG (0.06)
0.43 aBA
(0.02)
0.41 aDC (0.01)
12
0.44 aIHG
(0.03)
0.36 aBDC (0.03)
0.37 aDE (0.02)
15
0.51 aFCEDG (0.04)
0.39 aBDAC (0.05)
0.40 aDC (0.01)
18
0.55 aFCEBDG (0.09)
0.40 aBAC (0.02)
0.42 aC
18
0.48 aFEHG
(0.02)
0.36 bBDC (0.05)
0.37 bDE (0.01)
21
0.58 aCEBD
(0.04)
0.40 bBAC (0.02)
0.40 bDC (0.01)
24
0.62 aCB
(0.11)
0.42 aBA
(0.03)
0.46 aBA (0.01)
24
0.50 aFCEDG
(0.02)
0.36 bBDC (0.04)
0.40 bDC (0.01)
27
0.57 aFCEBD
(0.05)
0.39 bBDAC (0.06)
0.43 abBC (0.01)
30
0.65 aB
(0.08)
0.42 bBA
(0.02)
0.48 abA (0.01)
30
0.51 aFCEDG
(0.06)
0.38 bBDAC (0.03)
0.40 abDC (0.01)
33
0.60 aCBD
(0.02)
0.39 bBDAC (0.02)
0.43 bBC (0.01)
36
0.81 aA
(0.03)
0.45 bA
0.49 bA (0.02)
numerical number in the table presented
(0.01)
(0.01)
x (SD)
a Control; after 6 hr per day the oil was filtered with filter paper for 6 days. b Com I (3:4:1 of bentonite, activated carbon, and celite); after 6 hr per day the oil was filtered with filter paper and pass to adsorbent for 6 days. c Com II (3:4:1 of bentonite, activated clay, and celite + 1% citric acid); after 6 hr per day the oil was filtered with filter paper and pass to adsorbent for 6 days. a-b, A-I,
Means within a column with different letters are significantly different (p≤0.05). Means within a row with different letters are significantly different (p≤0.05).
Chapter 3 Utilization of mixed adsorbents to extend frying oil life cycle
47 Table 3.2 Changes in overall peroxide value in untreated and treated used oil during frying 36 hr Time (hr)
Control a
Com I b
Com II c
0
3.22 aG
(0.68)
3.59 aE
3
3.93 aG
(0.88)
3.93 aED (0.98)
4.62 aED (0.07)
6
7.65 aF
(0.06)
4.32 cECD (0.29)
5.79 bECD (0.14)
6
8.57 aF
(0.10)
3.87 cED (0.47)
5.58 bED (0.43)
9
10.93 aDE (0.83)
5.70 bBC (0.98)
6.89 bBC
12
10.43 aE (0.65)
5.26 bBCD (0.93)
7.28 bBCD (0.40)
12
8.75 aF
(0.96)
7.50 abA (0.45)
5.74 bA
15
11.22 aDE (0.43)
3.84 cED (0.94)
7.83 bED (1.05)
18
13.68 aA (0.36)
3.32 cE
9.18 bE
18
12.15 aBDC (0.84)
6.30 cBA (0.43)
6.65 bBA (1.06)
21
12.14 aBDC (0.40)
3.51 cE
7.75 bE
24
11.40 aDEC (0.89)
4.06 cED (0.58)
8.15 bED (0.20)
24
11.61 aDEC (0.79)
3.44 cE
(0.61)
5.59 bE
(0.62)
27
11.94 aBDC (0.99)
3.31 cE
(0.62)
6.59 bE
(0.57)
30
13.18 aBA (0.42)
3.08 cE
(0.07)
9.25 bE
(0.49)
30
13.26 aBA (0.42)
5.89 bB
(0.29)
6.46 bB
(0.69)
33
12.26 aBDAC(0.50)
4.37 bECD (0.98)
6.67 bECD (0.69)
36
12.74 aBAC (0.94)
6.35 bBA (0.66)
7.03 bBA (0.88)
numerical number in the table presented
(0.84)
(0.69)
(0.40)
3.95 aE
(0.28)
(0.59)
(0.61)
(0.88)
(0.20)
x (SD)
a Control; after 6 hr per day the oil was filtered with filter paper for 6 days. b Com I (3:4:1 of bentonite, activated carbon, and celite); after 6 hr per day the oil was filtered with filter paper and pass to adsorbent for 6 days. c Com II (3:4:1 of bentonite, activated clay, and celite + 1% citric acid); after 6 hr per day the oil was filtered with filter paper and pass to adsorbent for 6 days. a-b, A-I,
Means within a column with different letters are significantly different (p≤0.05). Means within a row with different letters are significantly different (p≤0.05).
Chapter 3 Utilization of mixed adsorbents to extend frying oil life cycle
48 Table 3.3 Changes in overall dielectric constant in untreated and treated used oil during frying 36 hr Time (hr)
Control a
Com I b
0
2.30 aB (0.42)
1.83 aG
3
3.41 aA (0.30)
6
Com II c 1.92 aG
(0.11)
2.39 bEBDFC (0.13)
2.54 bFE
(0.06)
3.94 aA (0.12)
2.37 bEBDFC (0.07)
2.53 bFE
(0.11)
6
3.76 aA (0.35)
2.09 bGF
(0.13)
2.40 bF
(0.03)
9
3.52 aA (0.14)
2.13 cEGF
(0.11)
2.50 bFE
(0.09)
12
3.48 aA (0.60)
2.22 bEGDF (0.13)
2.69 abBDEC (0.13)
12
3.55 aA (0.64)
2.23 bEGDF (0.24)
2.60 abFDE (0.08)
15
3.58 aA (0.67)
2.42 aEBDFC (0.25)
2.77 aBDAC (0.09)
18
3.63 aA (0.67)
2.76 aBA
2.95 aA
18
3.64 aA (0.60)
2.35 bEBDFC (0.23)
2.63 abDEC (0.04)
21
3.64 aA (0.54)
2.55 aEBDAC (0.39)
2.81 aBAC (0.13)
24
3.82 aA (0.54)
2.66 bBAC
(0.13)
2.87 abBA (0.12)
24
3.81 aA (0.69)
2.35 bEBDFC (0.07)
2.66 abDEC (0.14)
27
3.83 aA (0.53)
2.44 bEBDFC (0.06)
2.79 bBDAC (0.01)
30
3.93 aA (0.56)
2.92 aA
(0.42)
2.91 aA
(0.10)
30
3.68 aA (0.46)
2.30 bEDFC
(0.14)
2.52 bFE
(0.13)
33
3.89 aA (0.37)
2.47 bEBDFC (0.13)
2.75 abBDAC (0.07)
36
4.33 aA (0.46)
2.59 bBDAC (0.07)
2.91 bA
numerical number in the table presented
(0.11)
(0.30)
(0.07)
(0.09)
x (SD)
a Control; after 6 hr per day the oil was filtered with filter paper for 6 days. b Com I (3:4:1 of bentonite, activated carbon, and celite); after 6 hr per day the oil was filtered with filter paper and pass to adsorbent for 6 days. c Com II (3:4:1 of bentonite, activated clay, and celite + 1% citric acid); after 6 hr per day the oil was filtered with filter paper and pass to adsorbent for 6 days. a-b, A-I,
Means within a column with different letters are significantly different (p≤0.05). Means within a row with different letters are significantly different (p≤0.05).
Chapter 3 Utilization of mixed adsorbents to extend frying oil life cycle
49 Table 3.4 Changes in overall lightness in untreated and treated used oil during frying 36 hr Time (hr)
Control a
Com I b
0
94.01 bA (0.69)
95.39 aA
3
93.17 aA (0.47)
80.77 cIH (0.81)
90.91 bC
6
81.62 bDCE (0.59)
83.93 bFG (1.32)
89.05 aDC (1.75)
6
85.66 bB
(0.62)
88.77 bDC (1.61)
93.96 aB
9
83.51 bC
(0.73)
82.24 bGH (1.28)
89.38 aDC (1.11)
12
77.49 aGH (0.04)
77.51 aJ
(1.88)
83.78 aHG (0.72)
12
80.66 cFE (0.28)
91.35 bBC
(0.45)
94.47 aB (0.07)
15
79.17 cGF
(0.38)
82.46 bFGH (0.79)
90.01 aC (0.89)
18
71.81 cJ
(1.08)
79.90 bIJH (1.22)
87.48 aDE (1.37)
18
80.78 cDFE (1.10)
88.01 bDE (0.52)
93.41 aB (0.05)
21
76.58 IcH (0.67)
81.53 bIGH (0.13)
89.01 aDC (0.41)
24
71.91 cJ
(0.30)
79.48 bIJH (0.04)
85.99 aFE (0.49)
24
80.49 cFE (0.71)
88.94 bDC (0.11)
93.65 aB (0.11)
27
74.83 bI
(1.04)
85.41 aFE (0.18)
84.63 aFG (0.51)
30
67.80 bK
(0.49)
78.57 aIJ
(0.07)
79.08 aI (0.26)
30
82.69 bDC (0.72)
92.51 aBA (0.11)
93.44 aB (0.40)
33
65.00 bL
82.04 aGH (0.24)
82.46 aH (0.85)
36
56.11 cM (1.08)
73.33 bK
85.95 aFE (1.45)
(0.64)
numerical number in the table presented
(0.19)
(0.85)
Com II c 96.49 aA (0.06) (0.20)
(1.01)
x (SD)
a Control; after 6 hr per day the oil was filtered with filter paper for 6 days. b Com I (3:4:1 of bentonite, activated carbon, and celite); after 6 hr per day the oil was filtered with filter paper and pass to adsorbent for 6 days. c Com II (3:4:1 of bentonite, activated clay, and celite + 1% citric acid); after 6 hr per day the oil was filtered with filter paper and pass to adsorbent for 6 days. a-b, A-I,
Means within a column with different letters are significantly different (p≤0.05). Means within a row with different letters are significantly different (p≤0.05).
Chapter 3 Utilization of mixed adsorbents to extend frying oil life cycle
50 Table 3.5 Changes in overall redness in untreated and treated used oil during frying 36 hr Time (hr)
Control a
Com I b
Com II c
0
-2.47 aA
(0.12)
-2.50 aA (0.30)
-2.21 aA
(0.18)
3
-4.18 aB
(0.13)
-3.51 aB
-3.81 aED
(0.10)
6
-5.30 aCD (0.26)
-5.30 aED (0.88)
-4.72 aI
(0.01)
6
-4.84 bCB
(0.40)
-3.75 aCB (0.35)
-3.98 abEGDF (0.21)
9
-5.38 aCED (0.40)
-4.87 aED (0.07)
-4.69 aI
(0.09)
12
-5.22 aCD (0.05)
-4.75 aD (0.67)
-4.47 aIH
(0.32)
12
-5.92 bFED (0.36)
-4.76 aD (0.25)
-4.33 aGH
(0.05)
15
-5.89 bFED (0.04)
-4.97 aED (0.29)
-4.48 aIH
(0.04)
18
-6.47 cF
(0.01)
-5.49 bED (0.09)
-4.74 aI
(0.04)
18
-6.06 cFED (0.14)
-4.72 bD (0.02)
-4.12 aEGHF (0.02)
21
-6.08 bFED (0.36)
-5.48 abED (0.58)
-4.33 aGH
24
-5.87 bFED (0.37)
-5.73 bE (0.55)
-4.18 aGHF (0.08)
24
-6.35 cFE
(0.03)
-5.17 bED (0.22)
-3.75 aD
27
-5.74 aCFED (1.14)
-5.53 aED (0.24)
-4.14 aEGHF (0.19)
30
-5.45 bCFED (0.78)
-5.39 bED (0.53)
-3.36 aB
30
-5.67 bCFED (0.69)
-5.29 bED (0.41)
-3.68 aCD (0.25)
33
-5.18 bCD (0.79)
-4.75 abD (0.46)
-3.13 aB
36
-4.75 aCB
-4.67 aCD (0.38)
-3.84 aEDF (0.07)
(0.64)
numerical number in the table presented
(0.53)
(0.12)
(0.08)
(0.43)
(0.11)
x (SD)
a Control; after 6 hr per day the oil was filtered with filter paper for 6 days. b Com I (3:4:1 of bentonite, activated carbon, and celite); after 6 hr per day the oil was filtered with filter paper and pass to adsorbent for 6 days. c Com II (3:4:1 of bentonite, activated clay, and celite + 1% citric acid); after 6 hr per day the oil was filtered with filter paper and pass to adsorbent for 6 days. a-b, A-I,
Means within a column with different letters are significantly different (p≤0.05). Means within a row with different letters are significantly different (p≤0.05).
Chapter 3 Utilization of mixed adsorbents to extend frying oil life cycle
51 Table 3.6 Changes in overall yellowness in untreated and treated used oil during frying 36 hr Time (hr)
Control a
0
9.75 aI
3
Com I b
Com II c
8.65 aK (0.51)
4.92 bJ
(0.43)
17.22 aH (1.04)
17.44 aJ
13.80 aI
(1.55)
6
21.29 aG (1.18)
21.62 aH (0.11)
22.48 aD
(1.08)
6
15.78 aH (0.92)
16.07 aJ
(0.82)
13.96 aI
(0.73)
9
21.28 aG (0.27)
19.70 aI (1.40)
19.42 aG
(0.53)
12
21.70 bG (0.62)
23.79 aG (0.21)
22.32 bED (0.07)
12
20.87 aG (1.73)
20.54 abIH (0.22)
17.33 bH
15
26.08 aF
(0.43)
25.34 aEFG (0.63)
21.25 bEDF (0.16)
18
28.74 aDE (0.76)
28.73 aCB (0.50)
24.65 bB
(0.21)
18
25.47 aF
(1.60)
20.82 bIH (0.86)
17.60 bH
(0.25)
21
29.00 aDC (1.19)
26.84 aED (0.06)
21.56 bEDF (0.94)
24
31.17 aC
30.05 aB
26.94 bA
24
26.55 aFE (1.74)
24.61 aFG (0.66)
20.90 bEGF (0.17)
27
29.28 aDC (1.47)
27.45 aCD (0.04)
22.27 bED (1.46)
30
34.47 aB (1.80)
32.16 aA (0.54)
24.14 bCB
(0.28)
30
29.27 aDC (0.01)
21.36 bIH (1.44)
17.45 cH
(0.35)
33
35.77 aAB (0.29)
24.07 bFG (0.75)
20.07 cGF
(0.30)
36
37.66 aA (1.14)
25.73 bEF (1.71)
22.77 bCD (1.31)
(0.68)
(0.16)
numerical number in the table presented
(0.69)
(0.51)
(0.20)
(0.40)
x (SD)
a Control; after 6 hr per day the oil was filtered with filter paper for 6 days. b Com I (3:4:1 of bentonite, activated carbon, and celite); after 6 hr per day the oil was filtered with filter paper and pass to adsorbent for 6 days. c Com II (3:4:1 of bentonite, activated clay, and celite + 1% citric acid); after 6 hr per day the oil was filtered with filter paper and pass to adsorbent for 6 days. a-b, A-I,
Means within a column with different letters are significantly different (p≤0.05). Means within a row with different letters are significantly different (p≤0.05).
Chapter 3 Utilization of mixed adsorbents to extend frying oil life cycle
Chapter 3 Utilization of mixed adsorbents to extend frying oil life cycle
Table 3.7 Summary of improvement ability d (%) of used frying oils at 18 hr and 36 hr with adsorbent combination 18 hr
36 hr
Sample FFA
PV
FOS
L*
a*
b*
FFA
PV
FOS
L*
a*
b*
Com I b
26.75
75.72
23.86
11.26
15.16
0.05
44.31
50.20
40.12
30.70
1.69
31.68
Com II c
13.74
32.87
18.62
21.82
26.66
14.25
41.61
44.86
32.83
53.19
19.11
39.53
numerical number in the table presented
x (SD)
b c
Com I (3:4:1 of bentonite, activated carbon, and celite); after 6 hr per day the oil was filtered with filter paper and pass to adsorbent for 6 days. Com II (3:4:1 of bentonite, activated clay, and celite + 1% citric acid); after 6 hr per day the oil was filtered with filter paper and pass to adsorbent for 6 days.
d
The recovery efficiency of adsorbents on used frying oils were calculated as follows with means data from table 3.1-3.6.
Improvement percentage =
Value of untreated oil – means of treated oil x 100 Value of untreated oil
52
CHAPTER 4 APPLICATION OF ADSORBENT AND OIL REPLENISHMENT FOR PROLONGING USEFUL OIL LIFE ABSTRACT Treatment of use frying oil with adsorbent combination and frequent replenishment were employed to improve the overall oil quality as indicating via free fatty acid (FFA) level, peroxide value (PV), FOS reading, and color parameters for L*, a*, b*. The 1% acid value of used oil with three different amounts of replenishment (10%, 20%, and 30%) every 2 hr were investigated. The higher replenishment level applied, the more oil quality obtained. As expectation, all the oils treated with adsorbent addition and replenishment refreshed the oil color and decreased (p≤0.05) FFA, PV, and FOS reading. In addition, the replenished oil with and 20% and 30% potentially retarded (p≤0.05) the oil deterioration and oxidation because of the dilution effect and the removal of polar constitutes created in the abused oil.
Keywords: adsorbent, frying oil, FFA, PV, FOS readings, oil replenishment
53
54
INTRODUCTION The quality of the frying oil and the quality of the food fried in that oil is intimately related (Blumenthal, 1991). Frying oil quality influences oil absorption and the types of by-products and residues absorbed by food. Repeated use of frying oil produces undesirable constituents that may pose health hazards. Therefore, the quality of frying oils is important to both food consumer and to the food service industry. The treatment and recovery of used frying oil thus is of commercial and economic importance to the food service industry. Frequent filtration treatment of frying oils have been found to improve oil service life by controlling build up of free fatty acids and removing insoluble particles. A filtration operation typically involves passing the used frying oil through a filter paper or cloth, which removes food bits and thereby reduce the chance of deterious reactions have been used to adsorb fat soluble degradation products as well as remove insoluble particles (Akoh et al., 2001). Lopez (1990) reported the solid contaminates in the oil can also accelerate the induction phase of oil breakdown. Thus, the filtration is method to slow oil breakdown by limiting the surface area available for attachment. Cleaning the oil with a filter is known. However, this is either not done at the right time, or continuously but to and inadequate extent and in a manner which results in the oil deteriorating, for example, as a result of the introduction of oxygen. Although coarse particles can be separate off in said manner, the very fine particles and the fatty acids oxidation product, or the water, remain present on the oil (Drijfthot et al., 1990). Currently, the oil is thus preferably filtered hot with mixed adsorbents (Friedman, 1982). Lin et al (2001) reported the filtration without adsorbent did not significantly change the color difference. In addition, the filtration could remove insoluble impurities generated in frying oil, which are believed to be detrimental to the stability of frying medium. The remained food debris and detached ingredients would dehydrate and char during frying, giving rise to the acceleration of fat deterioration and formation of color compound. Filtration with paper filter was recommended, which not only removes particles, but also adsorbs soluble deterioration product, including FFA, polar material, and color compounds. Saguy and Dana (2003) have defined of oil turnover; the oil turnover is the
Chapter 4 Application of adsorbent and oil replenishment for prolonging useful oil life.
55 ratio between the amount of oil in the fryer and the amount of oil consumed per hours. Typical industrial fryers are continuous and the recommended turnover is less than 8 hr. However, since fried food product and fryer is quite different, turnover time could vary significantly and could reach up to look or more in batch fryers such as these used in fast foods and restaurants (Lawson, 1995; Staffer, 1996). Filtration, replenishment and antioxidant addition improved the oil quality to some degree, and slowed the deterioration about 3.57-23.44%. Many researchers have studied the effect of various adsorbents agents have been improved quality of used frying oil. The exited served work attempting to explain in chemical product on quality of used frying oil (Lin et al., 2001: Bheemreddy et al., 2002: McNeill et al., 1986: Mancini-Filho et al., 1986: Munson et al., 1997: Mulflur et al., 1987: Duensing et al., 1978 and Seybold, 1995). Therefore, the objectives of this study were to investigate the effect of adsorbents combination with oil replenishment on physico-chemical characteristics of used frying oil recovery.
MATERIALS AND METHOD Materials
Food raw material Commercial breaded chicken drumsticks obtained from BETTER FOODS Co., Ltd. were used in this study. Fresh and clean chicken drumsticks were soaked in 15% seasoning solution containing salt, pepper, MSG, and STPP (BETTER FOODS Co., Ltd., Thailand) and subsequently predusted, steamed, battered and then individually powdered about 140g for each piece, with wheat flour, modified corn starch, water, salt, spices, sugar, artificial flavor, paprika powder, and extracts of paprika in soy bean oil. The drumsticks were nearly uniform in shape and size (about 10 cm x 13 cm x 3 cm) and weighed approximately 140 g/piece. The temperature of the breaded drumsticks was at 45oC before frying. The initial moisture and fat content of the breaded drumsticks were 62.54% and 45.06%, respectively.
Frying oil
Chapter 4 Application of adsorbent and oil replenishment for prolonging useful oil life.
56 A used soybean oil 1% of acid value (AV) was taken from a commercial fryer after frying chicken drumstick meat continuously for 16 hr at 175oC from BETTER FOODS Co., Ltd. were used in this study. The coating ingredients of the fried meat include wheat flour, sugar, corn starch, salt, oleoresin paprika.
Adsorbents Four different adsorbents including celite (Celite® coarse 545, Fluka chemical, Buchs, Switzerland), activated clay (Power Dry Co., Ltd., Thailand), bentonite (Sigma Aldrich Chemica, GmbH, Germany), and citric acids were used to examine on adsorption capability of polar degradation products in the used oils. Celite was a white powder, odorless powder composed of silicon dioxide (SiO2); activated clay was gray granules, odorless, insoluble in water composed of calcium alumino silicate; bentonite was light brown in color, odorless powder composed of silicon dioxide (SiO2), aluminum dioxide (Al2O3)
Adsorbent combination
For the adsorbent combinations used in this experiment were consisting of 3:4:1 of bentonite, activated clay, and celite + 1% of citric acid. The selection of the types of adsorbent and their appropriate ratio was based on our preliminary study.
The frying experiment
The frying experiment was composed of five different treatments. The frying treatment labeled ‘control” contained oil without adding adsorbents but filtering with a regularly commercial filter paper pore size 30µ to remove the food crumbs and particulates at the end of each frying day. The treatment 1 contained oil with adding the mixed adsorbents and using filtration system but no replenishment (every two hr) of oil. The other treatments labeled as ‘treatment 2’, ‘treatment 3’, and ‘treatment 4’ was similar to treatment 1 but the replenishment of the oil was employed at three different levels (10%, 20% and 30%, respectively). Thus, treatment 2, 3, and 4 contained the used oil replenishment with 10%, 20% and 30% of 1% AV oil, respectively. Then, all the treatments were to evaluate the efficiency of the processing Chapter 4 Application of adsorbent and oil replenishment for prolonging useful oil life.
57 techniques for prolonging the useful life of frying oil. Each frying treatment was conducted for 3 days long attempting to simulate the commercial industrial frying. Fryer was switched on for 6 hr per day. Thirty six batches of powdered chicken drumsticks were continuously fried per day to mimic the same amount of frying load/oil used in this manufacturing. Each batch consisting of four powered chicken drumsticks was fried at 10 min intervals.
Frying test
The powdered drumsticks were fried in a commercial dual-unit electric batch fryer Model H 114-2 CSC (Fry-master, Shreveport, LA, USA) with a capacity of 21 liters of frying oils. The model of fryer is shown in figure 3.1. Before frying, used oil was preheated at 175oC for 30 min to simulate to normal frying condition. The frying oil was maintained at +5oC of the set temperature (175oC) using a programmable temperature controller. In addition, no fresh oil was added during frying. However, in the beginning of the next frying date, the small amount of 1% AV used oil about 200 ml per day might be added in the fryer to keep the initial oil level constantly. Four powered chicken drumsticks about 560g were randomly fried in 13 kgs of heated oil. Each batch of the chicken drumsticks was fried at a temperature of 175oC. For each frying cycle, the chicken samples were fried for 150 sec and then the temperature of frying oil was kept at 175oC for the rest of frying cycle even if unloading food materials. The gap timing between each frying cycle provided time for the next batch preparation and permitted the fryer to make up any loss in temperature. The chicken samples were placed in a stainless basket to keep them submerged. The fried samples were immediately withdrawn from oil and cooled to the ambient temperature.
Oil filtration
At the end of each day, after the last batch of frying, gravity filtration method was used to filter the used oil. The hot oil from the fryer pot was collected into an oil container and then recirculated and filtrated under vacuum condition with filter paper as recognized as the control. The filter paper obtained from (Noonsfeer Co., Ltd., Thailand). The oil from the fryer pot was filtered in order to remove the food crumbs Chapter 4 Application of adsorbent and oil replenishment for prolonging useful oil life.
58 and batter sediments. Similarly, oils in ‘treatment 1’, ‘treatment 2’, ‘treatment 3’, and ‘treatment 4’ were gravity filtered, treated with 1% (by weight) adsorbents, and then recirculated for passing through the filter paper. After continuously poured and stirred to the recirculated oil for 5 min, the adsorbent particles were ultimately recovered and separated from the used oil via vacuum filtration system for 20 min. The model of portable mobile filtration system is shown at figure 3.1.
Oil sample collection
The frying oil was randomly collected every 2 hr. The oil samples were individually kept in closed container, sealed off with the cap in order to prevent the oxidation, then air cooled in dark room (approximately 7oC) for 1 hr after that keep at room temperature until the further physico-chemical analyses. The FFA, PV, FOS reading, and color parameters were measured with regard to express the deterioration rate of the oil.
Analysis tests of oil quality
Free Fatty Acid (FFA) Composition of free fatty acids was analyzed using AOCS procedure Ca 5a40. The designated quality of sample was weighted into Erlenmeyer flask. Next the specified amount of hot, neutralized alcohol 95% and 2ml phenolphthalein indicator was added into the flask. Finally the sample was titrated with 0.1N alkali, shaked vigorously until the appearance of the first permanent pink color of the same intensity as that of the neutralized alcohol before addition of the sample. The color must persist for 30 seconds (AOCS, 1990). The test was duplicated.
Peroxide value (PV) Peroxide value was determined by AOCS procedure Cd 8-53 (AOCS, 1990). The test was duplicated.
Dielectric Constant The dielectric property of all samples was measured by Food Oil Sensor (model NI-2C, Northern Instrument Co., Lino Lakes, MN). In general, the test Chapter 4 Application of adsorbent and oil replenishment for prolonging useful oil life.
59 consisted of two steps. In first step, the instrument was equilibrium balanced to a zero state with the fresh oil used in the frying process. A few of the fresh oil or test oil drops onto open test cell, containing a heater and temperature controller. The dielectric properties of oil normally varied due to the different in oil source and the oil temperature, it is essential that all readings must be taken at the same temperature. The awareness of the difference in fresh and tested oil samples was essential concern and the temperature of both oils required the same. After, calibrated using fresh oil to zero, the fresh oil was then removed from the instrument cup with soft tissue paper; suddenly the tested oil samples were added in the cup to measure the change in dielectric constant. The test was performed in duplicated.
Color The equipment used for determining oil color was a Tintometer (model PFX190, Lovibond, England). Color of frying oils was measured at the L*, a*, and b* values. Three color readings were taken from each oil sample and the average was used for analysis.
Statistical methods
Statistic analyses were performed using General Linear Model Program (GLM) to test the capability of the adsorbent combinations for improving frying oil quality and prolonging frying oil life in commercial frying scale. Least Significant Difference (LSD) was used to estimate the significant differences among the means of each treatment at 5% the probability level using SAS program (SAS, 2000).
RESULTS AND DISCUSSION As expected, all oil samples treated with adsorbent exhibited the excellent oil quality improvement (p≤0.05) as indicated by FFA, PV, and FOS readings when compared to the control. The graphical patterns of FFA formation, PV change, and elevation of FOS in this chapter were similar to those in chapter 3. By the end of 18 hr of frying without adsorbent treatment, all the quality indexes were more than the oil treated by adsorbent addition corporated with replenishment in every level. It could
Chapter 4 Application of adsorbent and oil replenishment for prolonging useful oil life.
60 conclude that the addition of adsorbent into the used oil could remove the polar material components (as indirectly expressed by FOS readings) occurring due to the oil deterioration, and lipid oxidation. Contrary to the filtration without the application of adsorbents, the daily filtration treatment (the control), not only removed more FFA each time of treatment, but it also could not controlled the FFA build-up, and kept the level of FFA more than 2.0% at the end of 18 hr frying (fig.4.1). The FFA value of control at the beginning frying was 0.96% and then reached 2.32% after 18 hr of continuous frying. The steep slope of all oil quality indexes at the end of the day for the control sample was higher (p≤0.05) than the other treatments with adsorbent addition and replenishment. The steep slope of FFA curve in the same day caused by the action of adsorbent added in the oil. The FFA of the oil treated with adsorbent perpendicularly dropped due to chemical adsorption and replenishment effects. That result was related to suggestion of Lin et al. (2001), and Saguy and Dana (2003). The PV of replenished oils with 20% and 30% cooperated with adsorbent combination might be stable and did not change a lot as compared to the others. As expected, the replenished oils cooperated with adsorbent combination had s significant (p≤0.05) decrease in peroxide values (table 4.2). This might be benefits to control the PV during frying operation. The FOS readings at treatment 3 and 4 were not significantly (p≤0.05) different from control (table 4.3). As expected, the oil in both treatments could be standing the heat deterioration due to dilution effects. At 18 hr, the control oil expressed the highest value of FOS readings when compared to the others. However, after 18 hr of frying, all the oil samples had FOS readings more than 4. Thus, these oils needed to discard at 8 hr of frying. The color data exhibited in the figure 4.4. The oils treated with replenished 20% and 30% cooperated with adsorbents were significantly (p≤0.05) lighter, less yellow and red than the control. The control sample, all parameters of color data had tendency rapidly to darker, red, and yellow than the other treatment. Because of that are effects from heating and seasonings, while exposed to the used oil during frying. Incorporated adsorbent combination, the oil replenishment each level would be more effective on remove color compounds and effective to dilution chemical component. The replenishment technique significantly improved the oil quality to some degree, and slowed the deterioration (fig. 4.1 - 4.4) due to the dilution effect and removal of charcoal particles. According to figure 4.1-4.4, it found that the used oil Chapter 4 Application of adsorbent and oil replenishment for prolonging useful oil life.
61 replenished with higher amount of 1% AV oil showed more possibility to prolong the useful of oil life. The oil replenished with 20% and 30% also exhibited the same oil quality indexes in order to reduce the formation of FFA, PV, and FOS readings. Simultaneously replenishing with used after filtration could dilute the remaining degradation products and flavor of fried food, reduce viscosity, formation tendency and colors. However, the remain soluble degradation products, such as FFA are more susceptible to oxidation, and could lead to further decomposition due to free radical reactions (Lin et al., 2001). Incorporated with filtration system, the oil replenishment would be more effective than the only use of filtration. Thus, filtration with filter aid was recommended, which not only removes particles, but also adsorbs soluble deterioration products, including FFA, polar materials, and color compounds. In general, filtration could remove insoluble impurities generated in frying oil, which are believed to be detrimental to the stability of frying medium. However, the effectiveness of this method to extend the oil life was not good enough. Thus, the remained food debris and detached ingredients would dehydrate and char during frying, giving raise to acceleration of fat deterioration and formation of color compounds. Some researchers had reported that an 8 hr turnover rate was reported to control FFA level within 0.6-0.8% for 500 h (Saguy and Dana, 2003).
CONCLUSION The 1% AV used oil with three different amounts of replenishment (10%, 20%, and 30%) every 2 hr were investigated. The higher replenishment level applied, the more oil quality obtained. As expectation, all the oils treated with adsorbent addition and replenishment refreshed the oil color and decreased (p≤0.05) FFA, PV, and FOS reading. In addition, the replenished oil with and 20% and 30% potentially retarded (p≤0.05) the oil deterioration and oxidation because of the dilution effect and the removal of polar constitutes created in the abused oil.
REFERENCES Akoh CC, Reynolds AE. 2001. Recovery of used frying oils. U.S. patent 6,187,355 B1.
Chapter 4 Application of adsorbent and oil replenishment for prolonging useful oil life.
62 AOAC Assoc. Official Analytical Chemists. 1995. The official methods of analysis. 16th ed., vol. 2, Arlington, Va.: AOAC. Bheemreddy RM, Chinnan MS, Pannu KS, and Reynolds AE. 2002. Active treatment of frying oil for enhanced fry-life. J Am Oil Chem Soc 67(4):147884. Blumenthal, M.M. 1991. A new look at the chemistry and physics of deep fat frying. Food Technol. 45(2): 68-72, 94. Boki K, Shinoda S, Ohno S. 1989. Effects of filtering through bleaching media on decrease of peroxide value of autoxidized soybean oil. J Food Sci 54(6): 1601-3. Che Man YB, Jaswir I. 2000. Effect of rosemary and sage extracts on frying performance of refined, bleached and deodorized (RBD) palm olein during deep-fat frying. Food Chem 69: 301-7. Duensing WJ, Miga CJ. 1978. Cooking oil treating system and composition. U.S.patent 4,112,129. Lin S, Akoh CC, Reynolds AE. 1998. The recovery of used frying oils with various adsorbents. J Food Lipids 5: 1-16. Lin S, Akoh CC, Reynolds AE. 1999. Determination of optimal conditions for selected adsorbent combinations to recover used frying oils. J Am Oil Chem Soc 76(6): 739-44. Lin S, Akoh CC, Reynolds AE. 2001. Recovery of used frying oils with adsorbent combinations: refrying and frequent oil replenishment. Food Res Int 34: 15966. Mancini-Filho J, Smith LM, Creveling RK, and Al-Shaikh HF. 1986. Effects of selected chemical treatments on quality of fat used for deep frying. J Am Oil Chem Soc 63(11): 1452-6. McNeill J, Kakuda Y, Kamel B. 1986. Improving the quality of Used Frying oils by treatment with activated carbon and silica. J Am Oil Chem Soc 63(12): 15647. Mounson JR, Bryan LB, Caldwell JD. 1997. Treatment of cooking oils and fats with magnesium silicate and alkali materials. U.S. patent 5,597,600. Mulflur WT, Munson JR. 1987. Treatment of cooking oils and fats. U.S. patent 4,681,768. Seybold JC. 1995. Method of frying oil treatment using an alumina and amorphous Chapter 4 Application of adsorbent and oil replenishment for prolonging useful oil life.
63 silicon composition. U.S. patent 5,391,385. Yates RA, Caldwell JD. 1992. Adsorptive capacity of active filter aids for used cooking oil. J Am Oil Chem Soc 69(9): 894-7. Yates RA, Caldwell JD. 1993. Regeneration of oils used for deep frying: A comparison of active filter aids. J Am Oil Chem Soc 70(5): 507-51.
Chapter 4 Application of adsorbent and oil replenishment for prolonging useful oil life.
64
Free fatty acid
2.30
1.80
1.30
0.80 0
2
Control
4
6
Treated 1
8
Time (hr)
10
Treated 2
12
14
Treated 3
16
18
Treated 4
Figure 4.1 Average FFA values obtained for oil samples at different percentage oils replenishment with adsorbent combination.
Chapter 4 Application of adsorbent and oil replenishment for prolonging useful oil life.
65 27
Peroxide value
23
19
15
11
7 0
2
Control
4
6
Treated 1
8
Time (hr)
10
Treated 2
12
14
Treated 3
16
Treated 4
Figure 4.2 Average PV values obtained for oil samples at different percentage oils replenishment with adsorbent combination.
Chapter 4 Application of adsorbent and oil replenishment for prolonging useful oil life.
18
FOS Reading
66
6.2 6.0 5.8 5.6 5.4 5.2 5.0 4.8 4.6 4.4 4.2 4.0 3.8 3.6 3.4 3.2 3.0 0
2
4
6
8
10
12
14
16
18
Time (hr) Control
Treated 1
Treated 2
Treated 3
Treated 4
Figure 4.3 Average dielectric constant obtained for oil samples at different percentage oils replenishment with adsorbent combination.
Chapter 4 Application of adsorbent and oil replenishment for prolonging useful oil life.
Lightness (L*)
67
60.0 59.0 58.0 57.0 56.0 55.0 54.0 53.0 52.0 51.0 50.0 49.0 48.0 47.0 46.0 45.0
18.5
Redness (a*)
16.5 14.5 12.5 10.5 8.5 48.0
Yellowness (b*)
46.0 44.0 42.0 40.0 38.0 36.0 0
2
4
6
8
10
12
14
16
18
Time (hr) Control
Treated 1
Treated 2
Treated 3
Treated 4
Figure 4.4 Average L*, a*, and b* obtained for oil samples at different percentage oils replenishment with adsorbent combination.
Chapter 4 Application of adsorbent and oil replenishment for prolonging useful oil life.
Chapter 4 Application of adsorbent and oil replenishment for prolonging useful oil life.
Table 4.1 FFA values for oil samples at different percentage oils replenishment with adsorbent combination and filtration system. Time (hr)
Treatment 1a
Treatment 2 b
Treatment 3 c
Treatment 4 d
Treatment 5 e
0
0.96 aJ
(0.01)
0.95 aH (0.01)
0.96 aG (0.01)
0.98 aF
(0.04)
0.97 aE (0.01)
2
1.03 aI (0.01)
1.04 aG (0.02)
1.01 aFG (0.02)
1.01 aF
(0.02)
1.00 aDE (0.01)
4
1.11 aGH (0.02)
1.11 aF (0.01)
1.08 aEF (0.03)
1.13 aCD (0.01)
1.12 aC (0.02)
6
1.27 aF
(0.03)
1.26 aE (0.04)
1.17 aD (0.03)
1.16 aBCD (0.01)
1.18 aB (0.02)
6
1.15 aGF (0.06)
0.98 bGH (0.03)
0.97 bG (0.04)
1.03 bEF
(0.02)
1.04 bD (0.01)
8
1.44 aE (0.01)
1.16 bF (0.05)
1.09 bEF (0.03)
1.12 bCD (0.01)
1.11 bC (0.01)
10
1.64 aC (0.02)
1.29 bDE (0.01)
1.20 cCD (0.01)
1.12 dCD (0.01)
1.13 dC (0.03)
12
1.87 aB (0.03)
1.38 bC (0.01)
1.26 cC (0.01)
1.22 dcB (0.03)
1.20 dB (0.01)
12
1.56 aD (0.01)
1.01 cGH (0.04)
1.04 cbF (0.01)
1.10 bDE (0.03)
1.10 bC (0.03)
14
1.93 aB (0.01)
1.33 bDC (0.05)
1.15 cDE (0.06)
1.16 cBCD (0.05)
1.17 cB (0.03)
16
2.07 aHI (0.01)
1.72 bB (0.04)
1.35 cB (0.01)
1.19 dBC (0.03)
1.21 eB (0.02)
18
2.32 aA (0.01)
1.99 aA (0.02)
1.66 bA (0.02)
1.44 cA (0.09)
1.28 cA (0.01)
numerical number in the table presented
x (SD)
a Untreated oil, after 6 hr per day the oil was filtered with paper filter for 3 day. b Treated oil, after 6 hr per day the oil was filtered with paper filter and pass to adsorbent combination (bentonite: activated clay: celite=3:4:1+1% citric acid) for 3 days. c-e Treated oil; oil replenishment 10%, 20%, and 30% every 2 hr, after 6 hr per day the oil was filtered with paper filter and pass to adsorbent combination (bentonite: activated clay: celite=3:4:1+1% citric acid) for 3 days. a-b, Means within a column with different letters are significantly different (p≤0.05). A-I, Means within a row with different letters are significantly different (p≤0.05).
68
Chapter 4 Application of adsorbent and oil replenishment for prolonging useful oil life.
Table 4.2 Peroxides values for oil samples at different percentage oils replenishment with adsorbent combination and filtration system. Time (hr)
Treatment 1a
Treatment 2 b
Treatment 3 c
Treatment 4 d
Treatment 5 e
0
8.64 aG
(1.15)
8.00 aG (0.20)
8.05 aI
(0.08)
7.43 aF
(0.06)
7.66 aE
2
12.89 aF
(0.21)
12.27 aF (0.72)
11.80 aH
(2.49)
12.16 aE
(0.12)
13.41 aDC (0.17)
4
13.97 aF
(1.52)
15.16 aE (0.85)
13.96 aFG (0.36)
12.94 aDE (1.24)
15.42 aABC (0.23)
6
17.86 aE
(0.09)
17.63 aD (0.15)
15.99 bE
(0.30)
14.12 bBCD (0.05)
15.95 cAB (0.33)
6
18.65 aE
(1.18)
15.26 bE (0.68)
12.92 cbGH (1.30)
13.41 cbCDE (0.21)
12.47 cD (1.00)
8
21.21 aD
(0.38)
17.80 bD (0.09)
15.84 cbEF (0.05)
13.54 cCD (0.37)
13.80 cCD (2.63)
10
21.85 aCD (0.27)
21.12 aC (1.46)
22.90 aCD (0.88)
14.87 bAB
(0.17)
13.78 bCD (0.38)
12
23.56 aB
(0.23)
24.73 bAB (1.27)
25.52 abAB (0.11)
14.72 cABC (0.09)
16.72 dA (1.03)
12
22.26 aBCD (0.68)
20.15 bC (0.80)
21.12 abD (0.58)
16.00 cA
(0.48)
14.42 dBCD (0.36)
14
23.32 aBC (0.69)
23.70 aB (0.26)
23.93 aBC (0.18)
14.40 bBC
(0.21)
14.36 bBCD (0.45)
16
23.81 abB (0.11)
25.54 aA (0.12)
23.51 bC
(0.08)
15.04 cAB
(0.99)
15.30 cABC (1.37)
18
25.77 aA (0.16)
26.28 aA (0.31)
26.04 aA
(0.13)
15.42 bAB
(1.18)
16.15 bAB (0.12)
numerical number in the table presented
(0.28)
x (SD)
a Untreated oil, after 6 hr per day the oil was filtered with paper filter for 3 day. b Treated oil, after 6 hr per day the oil was filtered with paper filter and pass to adsorbent combination (bentonite: activated clay: celite=3:4:1+1% citric acid) for 3 days. c-e Treated oil; oil replenishment 10%, 20%, and 30% every 2 hr, after 6 hr per day the oil was filtered with paper filter and pass to adsorbent combination (bentonite: activated clay: celite=3:4:1+1% citric acid) for 3 days. a-b, Means within a column with different letters are significantly different (p≤0.05). A-I, Means within a row with different letters are significantly different (p≤0.05).
69
Chapter 4 Application of adsorbent and oil replenishment for prolonging useful oil life.
Table 4.3 FOR reading values for oil samples at different percentage oils replenishment with adsorbent combination and filtration system Time (hr)
Treatment 1a
Treatment 2 b
Treatment 4 d
Treatment 5 e
0
3.35 aF (0.28)
3.08 aG (0.13)
3.11 aF
(0.01)
3.16 aF (0.08)
3.07 aH (0.11)
2
3.45 aF (0.12)
3.66 aF
3.58 aEF
(0.11)
3.57 aE (0.16)
3.32 aG (0.16)
4
3.57 aEF (0.18)
3.78 aEF (0.15)
3.76 aDE (0.31)
3.61 aE (0.15)
3.56 aF
6
3.63 aEF (0.24)
3.85 aEF (0.15)
3.96 aCDE (0.13)
4.04 aCD (0.16)
3.80 aDE (0.16)
6
3.60 bEF (0.13)
3.79 abEF (0.11)
3.82 abE (0.11)
3.89 aD (0.09)
3.70 abEF (0.07)
8
4.03 aDE (0.18)
4.15 aDE (0.05)
4.13 aCD (0.04)
4.13 aC (0.04)
3.92 aD (0.10)
10
4.70 aBC (0.39)
4.46 aCD (0.21)
4.39 aBC (0.06)
4.22 aBC (0.08)
4.20 aC (0.08)
12
4.37 aCD (0.37)
4.52 aCD (0.05)
4.78 aB
(0.19)
4.41 aB (0.03)
4.37 aC (0.03)
12
4.17 bD (0.03)
4.40 aCD (0.02)
4.46 aBC (0.12)
4.20 bBC (0.09)
4.20 bC (0.01)
14
5.04 aB (0.12)
4.69 bBC (0.08)
4.89 abB
(0.13)
4.40 cB (0.04)
4.37 cC (0.03)
16
5.82 aA (0.10)
5.01 abB (0.06)
5.45 abA (0.44)
4.92 bA (0.10)
4.60 bB (0.05)
18
6.21 aA (0.11)
5.48 bcA (0.48)
5.57 abA (0.55)
5.13 bcA (0.02)
5.07 cA (0.15)
numerical number in the table presented
(0.25)
Treatment 3 c
(0.04)
x (SD)
a Untreated oil, after 6 hr per day the oil was filtered with paper filter for 3 day. b Treated oil, after 6 hr per day the oil was filtered with paper filter and pass to adsorbent combination (bentonite: activated clay: celite=3:4:1+1% citric acid) for 3 days. c-e Treated oil; oil replenishment 10%, 20%, and 30% every 2 hr, after 6 hr per day the oil was filtered with paper filter and pass to adsorbent combination (bentonite: activated clay: celite=3:4:1+1% citric acid) for 3 days. a-b, Means within a column with different letters are significantly different (p≤0.05). A-I, Means within a row with different letters are significantly different (p≤0.05).
70
Chapter 4 Application of adsorbent and oil replenishment for prolonging useful oil life.
Table 4.4 Lightness values for oil samples at different percentage oils replenishment with adsorbent combination and filtration system. Time (hr)
Treatment 1a
Treatment 2 b
Treatment 3 c
Treatment 4 d
Treatment 5 e
0
59.57 aA
(0.73)
58.60 aABC (1.27)
58.37 aAB (0.54)
58.85 aA (0.60)
59.00 aA (0.11)
2
57.49 aABC (3.02)
58.14 aBCD (1.09)
57.63 aBC (0.41)
57.12 aBC (0.44)
58.33 aAB (0.56)
4
55.87 aBCD (1.30)
56.00 aE
56.36 aDE (0.24)
56.07 aCD (0.21)
57.38 aCD (0.37)
6
55.41 abCD (0.91)
55.33 abEF (0.20)
55.09 bF
(0.31)
55.40 abDE (0.62)
56.60 aEF
6
57.94 bAB
59.66 aAB
(0.53)
57.06 bDC (0.83)
58.34 abAB (0.74)
57.69 bBC (0.21)
8
55.94 bcBCD (0.16)
58.15 aBCD (0.32)
55.20 cEF (0.44)
56.21 bCD (0.60)
56.77 bDEF (0.06)
10
53.74 bDE (0.16)
56.68 aDE (0.59)
53.53 bG (0.30)
56.04 aCD (1.17)
55.67 aG
(0.49)
aG
(0.54)
bE
(0.42)
12
52.41
12
53.59 cDE (0.18)
60.12 aA
14
52.36 cE
16
48.45 cF
18
45.24
dG
(0.40)
bH
52.31
(0.28)
59.08 aA (0.91)
56.12 bCD (0.28)
57.18 bCDF (0.35)
(0.81)
57.68 aDC (0.06)
58.19 aABC (0.33)
55.99 bCD (1.10)
56.02 bGF (0.28)
(0.40)
53.99 abF
53.57 bG (0.01)
55.14 aDE (0.18)
55.30 aG
(0.31)
aH
(0.13)
numerical number in the table presented
49.72
cG
(1.24) (0.89)
51.48
bH
(0.88)
(0.62)
55.07
aDE
54.09
aE
(0.43)
(0.17)
55.49
(0.33)
(0.23)
(0.83)
55.05
aEF
(1.02)
53.77
x (SD)
a Untreated oil, after 6 hr per day the oil was filtered with paper filter for 3 day. b Treated oil, after 6 hr per day the oil was filtered with paper filter and pass to adsorbent combination (bentonite: activated clay: celite=3:4:1+1% citric acid) for 3 days. c-e Treated oil; oil replenishment 10%, 20%, and 30% every 2 hr, after 6 hr per day the oil was filtered with paper filter and pass to adsorbent combination (bentonite: activated clay: celite=3:4:1+1% citric acid) for 3 days. a-b, Means within a column with different letters are significantly different (p≤0.05). A-I, Means within a row with different letters are significantly different (p≤0.05).
71
Chapter 4 Application of adsorbent and oil replenishment for prolonging useful oil life.
Table 4.5 Redness values for oil samples at different percentage oils replenishment with adsorbent combination and filtration system. Time (hr)
Treatment 1a
0
9.11 aG (0.45)
8.50 aI
2
10.30 aF (0.19)
10.04 abH (0.12)
aE
Treatment 2 b
aF
(0.22)
Treatment 3 c
Treatment 4 d
Treatment 5 e
8.64 aK (0.42)
8.66 aI
(0.19)
8.70 aF
(0.30)
9.85 bJ
9.28 cHI
(0.05)
9.07 cEF
(0.08)
bI
(0.26)
cbFGH
cCD
4
12.86
6
13.11 aDE (0.22)
13.04 aEF (0.15)
12.26 bFG (0.52)
10.80 cDEF (0.08)
9.97 dBCD (0.11)
6
13.54 aDE (0.59)
11.74 bG (0.15)
11.11 bHI (0.54)
9.29 cHI
(0.11)
8.54 cF
8
13.99 aD (0.06)
12.92 bEF (0.53)
11.68 cGH (0.22)
9.80 dGH
(0.01)
9.55 dDE (0.12)
10
15.06 aC (1.10)
13.92 abCD (0.08)
13.09 bDE (0.17)
10.57 cEFG (0.15)
10.17 cBC (0.08)
12
15.65 aC (0.40)
14.52 bBC (0.21)
14.11 bBC (0.37)
12.02 cABC (0.05)
11.71 cA (0.21)
12
15.86 aC (0.81)
12.79 bF
(0.08)
12.64 bEF (0.45)
11.19 cCDE (0.34)
9.66 dCD (0.30)
14
16.96 aB (0.05)
13.52 bDE (0.14)
13.43 bCD (0.35)
11.63 cBCD (0.30)
10.33 dB
16
17.55 aB (0.15)
14.66 bB
(0.18)
14.35 bAB (0.11)
12.31 cAB
(0.59)
11.58 cA (0.23)
18
19.03 aA (0.26)
15.91 bA (0.65)
14.87 bA (0.16)
12.99 cA
(0..34)
12.03 cA (0.17)
(0.27)
numerical number in the table presented
12.47
(0.45)
10.72
(0.25)
10.03
(0.11)
9.65
(0.31)
(0.30)
(0.43)
x (SD)
a Untreated oil, after 6 hr per day the oil was filtered with paper filter for 3 day. b Treated oil, after 6 hr per day the oil was filtered with paper filter and pass to adsorbent combination (bentonite: activated clay: celite=3:4:1+1% citric acid) for 3 days. c-e Treated oil; oil replenishment 10%, 20%, and 30% every 2 hr, after 6 hr per day the oil was filtered with paper filter and pass to adsorbent combination (bentonite: activated clay: celite=3:4:1+1% citric acid) for 3 days. a-b, Means within a column with different letters are significantly different (p≤0.05). A-I, Means within a row with different letters are significantly different (p≤0.05).
72
Chapter 4 Application of adsorbent and oil replenishment for prolonging useful oil life.
Table 4.6 Yellowness values for oil samples at different percentage oils replenishment with adsorbent combination and filtration system. Time (hr)
Treatment 1a
Treatment 2 b
Treatment 3 c
Treatment 4 d
Treatment 5 e
0
36.60 aG (0.37)
36.18 aH (0.05)
36.39 aH (0.40)
36.35 aG (0.19)
36.62 aH (0.30)
2
37.18 abG (0.16)
37.63 aG (0.30)
37.10 abG (0.16)
36.97 abFG (0.35)
36.75 bGH (0.52)
4
38.71 aF (0.23)
38.57 aFG (0.15)
37.48 bG (0.09)
38.03 abEF (0.54)
37.74 bFGH (0.28)
6
40.02 aF (0.08)
40.19 aE (0.03)
38.94 bF (0.25)
38.91 bDE (0.76)
38.70 bEF (0.08)
6
39.39 aEF (0.11)
39.00 abF (0.30)
37.60 cG (0.08)
38.07 abcEF (1.06)
37.81 bcFG (0.45)
8
41.50 aD (0.06)
40.50 bE (0.55)
38.65 dF (0.19)
39.48 cD (0.20)
38.97 dcDE (0.27)
10
43.23 aC (0.45)
41.88 bD (0.71)
39.91 cE (0.33)
40.95 bcBC (0.26)
39.92 cCD (0.69)
12
44.16 aC (0.53)
44.20 aCB (0.62)
41.60 bD (0.39)
41.99 bB
(0.36)
41.09 bAB (0.20)
12
43.99 aC (0.94)
42.45 aD (0.30)
40.17 bE (0.09)
39.07 bDE (0.59)
39.26 bDE (0.71)
14
45.47 aB (0.50)
43.60 bC (0.61)
42.78 bC (0.14)
39.82 cCD (0.08)
40.02 cBCD (1.15)
16
47.01 aA (1.13)
44.79 bB (0.15)
43.77 bB (0.29)
41.92 cB
40.79 cBC
18
47.75
aA
(0.51)
numerical number in the table presented
46.31
abA
(0.63)
44.97
cbA
(0.21)
43.86
cA
(0.37) (1.24)
42.00
dA
(0.46) (0.18)
x (SD)
a Untreated oil, after 6 hr per day the oil was filtered with paper filter for 3 day. b Treated oil, after 6 hr per day the oil was filtered with paper filter and pass to adsorbent combination (bentonite: activated clay: celite=3:4:1+1% citric acid) for 3 days. c-e Treated oil; oil replenishment 10%, 20%, and 30% every 2 hr, after 6 hr per day the oil was filtered with paper filter and pass to adsorbent combination (bentonite: activated clay: celite=3:4:1+1% citric acid) for 3 days. a-b, Means within a column with different letters are significantly different (p≤0.05). A-I, Means within a row with different letters are significantly different (p≤0.05).
73
CHAPTER 5 SUMMARY The used frying oil in the food processing were tremendously prolonged and improved in oil life cycle using the adsorbent technology for decreasing the physicochemical changes such as color, and the rate of oil deterioration (indicated using FFA, PV and FOS Reading). For instant, the frying oil with com I (bentonite: activated carbon: celite 545 3: 4: 1) reduced FFA, PV, and FOS readings 44.31%, 50.20%, and 40.12%, respectively, while com II (bentonite: activated clay: celite; 3: 4: 1 mixed with citric acid 1% w/w) reduced 41.61%, 44.86%, and 32.83%, respectively. In addition, com I and com II increased color parameters indexes L*, a*, and b* were 30.70%, 53.19%, and 1.69%, 19.11%, and 31.68%, 39.53%, respectively. The L* applied, the more oil quality obtained for the physical properties. The future feasibility to use adsorbent combination with filtration system and oil turn over rate for improved in frying oil life. Treatment of use frying oil with adsorbent combination and frequent replenishment were employed to improve the overall oil quality as indicating via free fatty acid (FFA) level, peroxide value (PV), FOS reading, and color parameters for L*, a*, and b*. The 1% AV used oil with three different amounts of replenishment (10%, 20%, and 30%) every 2 hr were investigated. The higher replenishment level applied, the more oil quality obtained. As expectation, all the oils treated with adsorbent addition and replenishment refreshed the oil color and decreased (p≤0.05) FFA, PV, and FOS reading. In addition, the replenished oil with and 20% and 30% potentially retarded (p≤0.05) the oil deterioration and oxidation because of the dilution effect and the removal of polar constitutes created in the abused oil.
74
VITA
Name
Chatchalai Siasakul
Home address
122/9 Soi Suksawat 26 Bangpakok Ratburana Bangkok
Education
Studying in Master Degree Institute: Silpakorn University Major: Master of Science (M.Sc.) Branch: Food Technology Highest Education Level: Bachelor Degree Institute: Maejo Institute of Agricultural and Technology Major: Bachelor of Science (B.Sc.) Branch: Food Technology High School Institute: Punyawarakun, Bangkok
Vita
