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SCIENTIFIC WORKS OF THE INSTITUTE OF HORTICULTURE, LITHUANIAN RESEARCH CENTRE FOR AGRICULTURE AND FORESTRY AND ALEKSANDRAS STULGINSKIS UNIVERSITY. SODININKYSTĖ IR DARŽININKYSTĖ. 2012. 31(1–2).
Quality changes of green onions stored in modified atmosphere Pranas Viškelis1, Ramunė Bobinaitė1, Liga Lepse2, Janis Lepsis2, Jonas Viškelis1 Institute of Horticulture, Lithuanian Research Centre for Agriculture and Forestry, Kauno 30, LT-54333 Babtai, Kaunas distr., Lithuania, e-mail
[email protected] 1
Pūre Horticultural Research Center, Abavas 2, Pūre, Tukumanovads, LV -3124 Latvia 2
The aim of this investigation was to evaluate the influence of modified atmosphere on the quality of green onion cv. ‘Parade’. Respiration rate, natural mass loss, and the influence of carbon dioxide on physiological parameters of green onions were analyzed. Additionally, total phenolics content and CIEL*a*b* colour coordinates of green onions were measured. The total phenolics content of green onions after 20 days of storage in modified atmosphere (10.0 % of CO2, temperature 0 ± 0.5 °C, relative humidity 95 %) reduced from 71.2 mg 100 g-1 to 66.5 mg 100 g-1, i. e. reduced only by 6.6 % from the initial phenolics content. There was no statistically significant difference between the radical scavenging capacity of green onions before and after storing them in modified atmosphere. After the storage in modified atmosphere the lightness index of green onions slightly increased (from 49.07 to 49.92), i. e. the onions became lighter, whereas the intensity of greenness slightly decreased (from -12.98 to -12.52). During green onion storage period the coordinate of yellowness increased (from 27.53 to 28.61), i. e. green onions were slightly more yellow after the storage. According to the results of this study, 20 days of storage in modified atmosphere does not have a significant negative effect on the quality of green onions. Key words: green onion, modified atmosphere, storage.
Introduction. Onions are one of the basic ingredients in cooking and their health benefits have been known for centuries. Some Allium vegetables (e. g., garlic, onion, leeks, chives, scallions) have been employed for millennia in the traditional medical practice to treat cardiovascular diseases. They have been shown to have 40
applications as antimicrobial, antithrombotic, hypolipidemic, antiarthritic and hypoglycemic agents (Corzo-Martinez et al., 2007; Sengupta et al., 2004). Recent epidemiological studies have shown that higher intake of Allium vegetables is associated with reduced risk of several types of cancers (Galeone et al., 2006). The cancer-protective effects of Alliums have been largely attributed to their content of organosulfur compounds (diallyl sulfide, diallyl disulfide) (Boukouvalas, Albert, 2012; Powolny, Singh, 2008). Green onions are highly valued for their flavour and nutritional value in supplying minor constituents, such as macro and micro minerals (potassium, calcium, magnesium, iron, selenium), and also vitamins (β-carotene, folate, vitamin A, vitamin C) (USDA National Nutrient Database for Standard Reference, 2011). Green onions contain high level of flavonoids (quercetin, kaempferol, luteolin) (Miean, Mohamed, 2001). Flavonoids are a large group of phenolic plant constituents. They have been shown to be highly effective scavengers of most types of oxidizing molecules, including singlet oxygen and various free radicals, which are possibly involved in DNA damage and tumor promotion (Le Marchand, 2002; Yao et al., 2004). The increasing popularity of minimally processed fruits and vegetables has been attributed to the increasingly recognized health benefits associated with the consumption of fresh produce, combined with the propensity of consumers to eat out or buy ready-to-eat and convenience foods (Neetoo et al., 2011). Green onions provide an interesting challenge as a minimally processed product. Green onions are comprised of roots, a compressed stem (sometimes called stem plate), and leaves, which consist of a lower white leaf sheath and the hollow upper green tissues. Minimal processing includes trimming of the leaves, cutting of the roots, and removal of all or part of the compressed stem. Although this results in a convenient fresh cut product, cutting damage, discoloration, dehydration, and decay are common defects of the cut surfaces (Hong et al., 2000). Therefore, it is important to choose the optimal storage conditions for green onions in order to provide a high quality product for fresh market, export and processing. Storage potential of green onions mainly depends on the cultivar, growing conditions and storage methods. Modified atmosphere can be used to supplement the maintenance of optimum temperature and relative humidity for preserving quality and reducing postharvest losses of fruits and vegetables during transportation and storage (Kader, 1994). Modified atmosphere storage is a control of atmosphere during storage and is achieved by the physiology of plant tissue either intentionally or unintentionally. There is less control over atmosphere composition during modified atmosphere storage than during controlled atmosphere storage. Depleted O2 and/or enriched CO2 levels can reduce respiration, delay ripening, decrease ethylene production, retard textural softening, slow down compositional changes associated with ripening, thereby resulting an extension in shelf life (Daş et al., 2006). The tolerance to low O2 varies between species and cultivars and is also time dependent. Therefore, the aim of this investigation was to evaluate the influence of modified atmosphere on the quality of green onion cv. ‘Parade’. The influence of carbon dioxide on physiological parameters of green onions was also analyzed. 41
Object, methods and conditions. Green onion cv. ‘Parade’ was grown in the Pūre Horticultural Research Center. In this study modified atmosphere was created passively through product respiration. For this purpose green onions were stored in hermetically closed glass containers, which were placed in the Besseling controlled atmosphere chambers (Besseling CA systems BV, Zwaag, The Netherlands). Respiration rate of green onions was measured with gas analyzer EASI-1 (Absoger, Les Barthes, France). The extracts for the total phenolics assay were obtained by extracting 5 g of homogenized green onions with 25 ml of methanol at ambient temperature for 1 h under constant shaking. The solution was filtered and the residue was repeatedly extracted with 25 mL of methanol for 1 h. The extracts were combined and diluted up to 50 mL with methanol. Total phenolics in the methanolic extracts were determined with Folin-Ciocalteu reagent according to the method of Slinkard and Singleton (1977). The absorbance of the samples was measured at 765 nm using the Genesys-10UV/Vis spectrophotometer (Thermo Spectronic, Rochester, USA). Results were expressed in mg of gallic acid equivalents (GAE) per 100 g of fresh weight. The extracts for the radical scavenging activity assay were obtained by extracting 5 g of homogenized green onions with 25 ml of methanol at ambient temperature for 2 h under constant shaking. The radical scavenging activity of extracts against stable 2,2-diphenyl-1-picrylhydrazyl hydrate DPPH• (Sigma-Aldrich, Germany) was determined by a slightly modified spectrophotometric method of Brand-Williams et al. (1995). DPPH• methanolic solution (2 mL, 6 × 10-5 M) was mixed with 20 µL of prepared extract. The decreasing absorbance at 515 nm due to the scavenging of DPPH• was measured with a spectrometer Genesys-10 UV/Vis. Simultaneously the absorption of blank sample containing the same amount of methanol and DPPH• solution was measured. Antiradical activity of the samples was expressed as Trolox equivalent antioxidant capacity TEAC. For this purpose calibration curve of Trolox was made in DPPH assay (r2 = 0.999). Ascorbic acid was determined by the titrimetric method using 2,6-dichlorphenolindophenol sodium salt solution (AOAC, 1990). Soluble solids content was measured using a refractometer (ATAGO pR-32, Atago Co., Ltd., Tokyo, Japan). Nitrate concentration was measured by a potentiometric method using the nitrate ion selective electrode (ECNO30301B) (Metodiniai nurodymai..., 1990). The surface color of green onions was measured with a portable spectrophotometer MiniScan XE Plus (Hunter Associates Laboratory, Inc., Reston, USA). CIEL*a*b*color parameters were recorded as L* (lightness), a* (+ redness/- greenness), b*(+ yellowness/ -blueness). The chroma (C*) and hue angle (h°) were also calculated (McGuiere, 1992). Experiment data were processed using Microsoft Office Excel (Microsof, USA). 42
Results and discussion. Fresh vegetables are metabolically active for long period after harvesting due to both endogenous activity, such as respiration, and external factors such as physical injury, microbial flora, water loss and storage temperature (Phillips, 1996). Respiration is the oxidative breakdown of complex substrate molecules normally present in plant cells (starch, sugars, organic acids) to simpler molecules such us CO2 and H2O. Since respiration rate is tightly related to the rate of metabolism, measurements of respiration provide an easy, non-destructive way to monitor the metabolic and physiological state of tissues (Saltveit, 2004). The CO2 released during respiration proportionally reduce respiration rate of green onions. Changes in respiration rate of green onions under modified atmosphere may be described by following polynomial equation y = 0.00001x2 - 0.0117x + 3.399, R² = 0.84 (Fig. 1.).
Fig. 1. Respiration rate of green onions at 0 ± 0.5 °C
1 pav. Svogūnų laiškų kvėpavimo intensyvumas laikant 0 ± 0,5 °C temperatūroje
Respiration rate of green onions strongly depends on the storage temperature (Fig. 2.). Under normal atmospheric conditions (0.03 % CO2, 21.03 % O2) at 0 °C respiration rate was 3.5 mg CO2/(kg • h), and at 5, 10 and 20 °C was 7.05, 14.19 and 57.56 mg CO2/(kg • h), respectively. Moisture loss or transpiration is an important physiological process that affects the main qualities of fresh fruits and vegetables such as saleable weight, appearance, texture and flavour. A loss in weight of only 5 % often causes fresh produce to lose freshness and appear wilted (Kang, Lee, 1998). Transpiration rate is influenced by factors such as surface area, respiration rate, temperature, humidity and air movement. 43
Fig. 2. Respiration rate of green onions at different temperatures
2 pav. Svogūnų laiškų kvėpavimo intensyvumas laikant skirtingoje temperatūroje
As it is shown in Fig. 3, lower storage temperature and higher CO2 concentration reduce respiration related mass loss of green onions.
Fig. 3. Mass loss of green onions due to respiration at different storage temperatures 3 pav. Masės nuostoliai dėl kvėpavimo laikant svogūnų laiškus skirtingoje temperatūroje
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Commodities that have high respiration rates require considerably more refrigeration than more slowly respiring produce. Modified atmosphere storage reduces vital heat by reducing respiration rate. Vital heat produced by the green onions at different storage temperatures under modified atmosphere (10 CO2) is given in Fig. 4. Vital heat of green onions at 20 °C was 22 times higher than that at 0 °C.
Fig. 4. The influence of temperature on vital heat of green onions under a modified atmosphere (10 % CO2) 4 pav. Temperatūros įtaka specifinei kvėpavimo šilumai modifikuotoje atmosferoje esant 10 proc. CO2
Individual crops are known to display a substantial range in respiratory rates and subsequent heat load placed on the cooling system (Peiris, Mallon, Kays, 1997). Therefore, the heat produced by respiration (vital heat), which is about 673 kcal for each mole of sugar (180 g) utilized, can be a major factor in establishing the refrigeration requirements (i. e., refrigeration capacity, air circulation, and ventilation) during transport and storage (Saltveit, 2004). The total phenolics content of green onions after 20 days of storage in modified atmosphere (10 % of CO2, temperature 0 ± 0.5 °C, relative humidity 95 %) reduced from 71.2 mg/100 g to 66.5 mg/100 g, i. e. reduced only by 6.6 % from the initial phenolics content (Table 1). There was no statistically significant difference between the TEAC values of green onions before and after storage in modified atmosphere (Table 1). Similarly, there were no significant differences between the ascorbic acid, soluble solids and nitrates contents of green onions before and after storage in modified atmosphere. Our results are in agreement with Sakaldaş et al. (2010), who reported that modified atmosphere packaging prevented the loss of vitamin C and degradation of phenolic compounds in dill leaves. In general, low O2 and high CO2 atmosphere 45
cause a decrease in polyphenoloxidase and ascorbic acid oxidase activity (Tian, Li, Xu, 2005; Saxena, Bawa, Raju, 2009). Table 1. Biochemical composition and DPPH-TEAC of green onions before and after storage in modified atmosphere 1 lentelė. Svogūnų laiškų biocheminė sudėtis ir DPPH-TEAC prieš laikymą modifikuotoje atmosferoje ir po jo
Green onions
Svogūnų laiškai
Before storage
Prieš laikymą
After storage Po laikymo
Ascorbic acid
Askorbo rūgštis,
mg/100 g
Tirpios sausosios medžiagos, %
Nitratai,
mg/kg
Phenolics DPPH Fenoliai, TEAC, mg/100 g µmol TE/g
8.4 ± 0.4
5.0 ± 0.10
197 ± 10
71.2 ± 6.2 1.12 ± 0.11
8.8 ± 0.6
4.8 ± 0.25
211 ± 12
66.5 ± 4.5 1.04 ± 0.08
Soluble solids
Nitrates
Data are expressed as means ± standard deviations (n = 3) / Duomenys pateikti kaip vidurkiai ± standartiniai nukrypimai (n = 3)
After the storage in modified atmosphere the lightness index (L*) of green onions slightly increased (from 49.07 to 49.92), i. e. the onions became lighter. Whereas the coordinate of greenness/redness (a*) reduced (from -12.98 to -12.52), which means that during the storage in modified atmosphere the intensity of green colour did not change significantly (Table 2). Table 2. CIEL*a*b colour parameters of green onions before and after storage in modified atmosphere
2 lentelė. Svogūnų laiškų CIEL*a*b spalvos rodikliai prieš laikymą modifikuotoje atmosferoje ir po jo Green onions
Svogūnų laiškai
Before storage Prieš laikymą
After storage
Po laikymo
L*
a*
b*
C*
h°
∆E
49.07 ± 0.60 -12.98 ± 0.23 27.53 ± 0.94 30.45 ± 0.94 115.49 ± 0.45 1.45 49.92 ± 1.23 -12.52 ± 0.65 28.61 ± 1.73 31.24 ± 1.83 114.17 ± 0.53
Data are expressed as means ± standard deviations (n = 3) / Duomenys pateikti kaip vidurkiai ± standartiniai nukrypimai (n = 3)
The coordinate of blueness/yellowness (b*) increased from 27.53 to 28.61, i. e. green onions were slightly more yellow after the storage in modified atmosphere. Loosing green pigmentation accompanied by the predominance of yellow pigments is a natural process in the senescence of many vegetables, and such changes can be accelerated by ethylene (Kasim M. O., Kasim R., Erkal, 2008). 46
The colour difference (∆E) between green onions before storage and after storage in modified atmosphere was only 1.45, which shows that storage in modified atmosphere did not have a significant influence on the colour of onions. In the range of 0 to 1 the colour differences (∆E) are not perceivable by the human eye; between 1 and 2 there are slight differences perceivable to a person capable of distinguishing nuances of colours; the range of 2 to 3.5 includes moderately high differences, easily perceived even by an inexperienced observer; values higher than 5 indicate large total colour differences (CIE, 1986). Conclusion. Modified atmosphere storage helps to preserve quality of green onions, thus extending their shelf life. According to the results of our study, 20 days of storage in modified atmosphere does not have a significant negative effect on the chemical composition and external quality of green onions. Acknowledgement. This work was supported by a grant from the EUREKA E! 5363 BaltVegStor, No.VP1-3.1-ŠMM-06-V-01-003. Gauta 2012 04 04 Parengta spausdinti 2012 05 16
References 1. AOAC. 1990. Vitamin C (ascorbic acid) in vitamin preparations and juices. In: K. Helrich (ed.), Official Methods of Analysis. 15th ed. AOAC Inc., Arlington, VA. 2. Boukouvalas J., Albert V. 2012. Regiospecific synthesis of cepanolide, a cancer chemoprotective micronutrient found in green onions. Tetrahedron letters, 53(24): 3 027−3 029. 3. Brand-Williams W., Cuvelier M. E., Berset C. 1995. Use of a free radical method to evaluate antioxidant activity. LWT – Food Science and Technology, 28(1): 25−30. 4. CIE. 1986. CIE Publication, Colorimetry. 2nd ed. Publication CIE No. 15.2. Vienna, Austria. 5. Corzo-Martinez M., Corzo N., Villamiel M. 2007. Biological properties of onions and garlic. Trends in Food Science and Technology, 18(12): 609−625. 6. Daş E., Gürakan G. C., Bayindirli A. 2005. Effect of controlled atmosphere, modified atmosphere packaging and gaseous ozone treatment on the survival of Salmonella Enteriditis on cherry tomatoes. Food Microbiology, 23(5): 430−438. 7. Galeone C., Pelucchi C., Levi F., Negri E., Franceschi S., Talamini R., Giacosa A., La Vecchia C. 2006. Onion and garlic use and human cancer. The American Journal of Clinical Nutrition, 82(5): 1 027−1 032. 8. Hong G., Peiser G., Cantwell M. I. 2000. Use of controlled atmospheres and heat treatment to maintain quality of intact and minimally processed green onions. Postharvest Biology and Technology, 20: 53−61.
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9. Kader A. A. 1994. Modified and controlled atmosphere storage of tropical fruits. In: B. R. Champ, E. Highley and G. I. Johnson (eds.), Postharvest handling of tropical fruits. Proceedings No. 50. The Australian Centre for International Agricultural Research (ACIAR), Canberra, 239−249. 10. Kang J. S., Lee D. S. 1998. A kinetic model for transpiration of fresh produce in a controlled atmosphere. Journal of Food Engineering, 35(1): 65−73. 11. Kasim M. U., Kasim R., Erkal S. 2008. UV-C treatments on fresh-cut green onions enhanced antioxidant activity, maintained green color and controlled ‘telescoping’. Journal of Food, Agriculture & Environment, 6(3&4): 63−67. 12. Le Marchand L. 2002. Cancer preventive effects of flavonoids – a review. Biomedicine & Pharmacotherapy, 56(6): 296−301. 13. McGuire R. G. 1992. Reporting of objective color measurement. HortScience, 27(12): 1 254−1 255. 14. Metodiniai nurodymai nitratams nustatyti augalininkystės produkcijoje. 1990. Vilnius. 15. Miean K. H., Mohamed S. 2001. Flavonoid (myricetin, quercetin, kaempferol, luteolin, and apigenin) content of edible tropical plants. Journal of Agricultural and Food Chemistry, 49(6): 3 106−3 112. 16. Neetoo H., Nekoozadeh S., Jiang Z., Chen H. 2011. Application of high hydrostatic pressure to decontaminate green onions from Salmonella and Escherichia coli O157:H7. Food Microbiology, 28(7): 1 275−1 283. 17. Peiris K. H. S., Mallon J. L., Kays S. J. 1997. Respiratory rate and vital heat of some specialty vegetables at various storage temperatutes. HortTechnology, 7(1): 46−49. 18. Phillips C. A. 1996. Review: Modified Atmosphere Packaging and its effects on the microbiological quality and safety of produce. International Journal of Food Science and Technology, 31(6): 463−479. 19. Powolny A. A., Singh S. V. 2008. Multitargeted prevention and therapy of cancer by diallyl trisulfide and related Allium vegetable-derived organosulfur compounds. Cancer Letters, 269(2): 305−314. 20. Sakaldaş M., Aslim A. Ş., Kuzucu C. Ö., Kaynaş K. 2010. The effects of modified atmosphere packaging and storage temperature on quality and biochemical properties of dill (Anethum graveolens) leaves. Journal of Food, Agriculture & Environment, 8(3 & 4): 21–25. 21. Saltveit M. E. 2004. Respiratory Metabolism. In: K. C. Gross, C. Y. Wang, M. E. Saltveit (ed.), The commercial storage of fruits, vegetables, and florists and nursery stock. Agriculture Handbook, No. 66. 22. Saxena A., Bawa A. S., Raju P. S. 2009. Phytochemical changes in fresh-cut jackfruit (Artocarpus heterophyllus L.) bulbs during modified atmosphere storage. Food Chemistry, 115(4): 1 443−1 449. 23. Sengupta A., Ghosh S., Bhattacharjee S. 2004. Allium vegetables in cancer prevention: an overview. Asian Pacific Journal of Cancer Prevention, 5(3): 237−245.
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24. Slinkard, K., Singleton, V. L. 1977. Total phenol analysis: automation and comparison with manual methods. American Journal of Ecology and Viticulture, 28(1): 49−55. 25. Tian S. P., Li B. Q., Xu Y. 2005. Effects of O2 and CO2 concentrations on physiology and quality of litchi fruit in storage. Food Chemistry, 91(4): 659–663. 26. USDA National Nutrient Database for Standard Reference. 2011. Release 24: Vegetables and vegetable products. In: Nutrient Data Laboratory Home Page. http://ndb.nal.usda.gov/ndb/foods/list. 27. Yao L. H., Jiang Y. M., Shi J., Tomas-Barberan F. A., Datta N., Singanusong R., Chen S. S. 2004. Flavonoids in food and their health benefits. Plant Foods for Human Nutrition, 59(3): 113−122. SODININKYSTĖ IR DARŽININKYSTĖ. SCIENTIFIC ARTICLES. 2012. 31(1–2).
Svogūnų laiškų kokybės pokyčiai laikant modifikuotoje atmosferoje P. Viškelis, R. Bobinaitė, L. Lepse, J. Lepsis, J. Viškelis Santrauka Darbo tikslas – įvertinti modifikuotos atmosferos įtaką ‘Parade’ veislės svogūnų laiškų kokybei. Ištirtas svogūnų laiškų kvėpavimo intensyvumas, natūralūs masės nuostoliai, anglies dvideginio koncentracijos įtaka fiziologiniams rodikliams, bendras fenolinių junginių kiekis bei CIEL*a*b* spalvų koordinatės. Nustatyta, kad bendras fenolinių junginių kiekis prieš laikymą buvo 71,2 mg 100 g-1, o palaikius 20 dienų 0 ± 0,5°C temperatūroje esant 95 % santykiniam drėgniui modifikuotoje atmosferoje, kai CO2 – 10,0 %, sumažėjo iki 66,5 mg 100 g-1, t. y. tik 6,6 % nuo pradinio kiekio. DPPH* radikalų surišimo aktyvumas beveik nepakito: prieš laikymą buvo 2,6 %, po laikymo – 2,8 %. Svogūnų laiškų šviesumo indeksas nuo 49,07 sąl. vnt. prieš laikymą padidėjo iki 49,92 sąl. vnt., t. y. laiškai pašviesėjo, žalios spalvos koordinatė a nuo -12,98 sąl. vnt. padidėjo iki -12,52 sąl. vnt., t. y. žalios spalvos intensyvumas nežymiai sumažėjo, duomenys statistiškai nepatikimi. Laikymo metu geltonos spalvos koordinatė b nuo 27,53 sąl. vnt. padidėjo iki 28,61 sąl. vnt., t. y. svogūnų laiškai truputį pagelto. Taigi svogūnų laiškų laikymas (iki 20 dienų) modifikuotoje atmosferoje neturėjo reikšmingos neigiamos įtakos jų kokybei. Reikšminiai žodžiai: laikymas, modifikuota atmosfera, svogūnų laiškai.
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