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KMID : 1134820180470040403
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Journal of the Korean Society of Food Science and Nutrition
2018 Volume.47 No. 4 p.403 ~ p.413
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Composition of Phenolic Compounds and Antioxidant Activities of Subcritical Water Extracts of Onion Skin
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Kim Dong-Shin
Lim Sang-Bin
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Abstract
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Onion skin was extracted using subcritical water at different temperature (100∼150°C) and time (5∼20 min), and content of individual phenolic compounds as well as total phenolic content (TPC), total flavonoid content (TFC), 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity, and ferric reducing antioxidant power (FRAP) were measured. Effect of CO2 addition to subcritical water was also measured. The sum of individual phenolic compounds at 120°C/10 min reached a maximum of 21.64 mg/g dry sample, which was 1.92 times higher than that of 80% ethanol extract. The contents of quercetin-3,4’-glucoside, quercetin-4’-glucoside, and quercetin reached maximum values at 120°C/10 min of 0.52, 3.39, and 8.87 mg/g dry sample, respectively and the content of quercetin was 1.59 times higher than that of 80% ethanol extract. Contents of protocatechuic acid, quercetin-3,4’-glucoside, quercetin-4’-glucoside, and quercetin increased by 1.58, 1.82, 2.38, and 2.89 times, respectively. The yield of protocatechuic acid was the lowest and yield of quercetin was the highest upon addition of 65 bar CO2 to subcritical water at 110°C/5 min. Therefore, it was possible to prevent quercetin destruction at high temperature by addition of CO2. TPC, TFC, DPPH radical scavenging activity, and FRAP reached maximum values of 62.4 mg gallic acid equivalents/g, 34.8 quercetin equivalents mg/g, 43.9 mg ascorbic acid equivalents/g, and 80.2 mmol Fe2+/100 g at 120°C/10 min, respectively, and increased by 3.17, 2.97, 2.48, and 2.54 times, respectively, upon addition of 65 bar CO2 to subcritical water at 110°C/5 min. The color values such as L, a, and b decreased upon increasing extraction temperature and time as well as addition of CO2. These results indicate that subcritical water extraction might be useful for extraction of individual phenolic compounds with high antioxidant activities in onion skins, and destruction of quercetin could be prevented at high temperature by addition of CO2 by decreasing extraction temperature and time.
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KEYWORD
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onion skin, subcritical water, phenolic compounds, CO2, antioxidant activity
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