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Subcritical water extraction of flavonol quercetin from onion skin

Subcritical water extraction of flavonol quercetin from onion skin
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대학원 식품공학과
이화여자대학교 대학원
Subcritical water could be an excellent alternative to organic solvent as a medium for extracting quercetin, due to its temperature-dependent selectivity, safety, efficiency of recovery, and lower cost. This study tested the use of subcritical water under high pressure (> 90 bar) at temperatures of 100―190℃ to extract quercetin from onion skin. The conditions for maximizing the extraction efficiency were determined by varying the temperature (100―190℃), static time (5―30 min), number of static cycles (1―3 cycles), particle size of onion skin (<1 mm, >10 mm), mixture ratio of onion skin and diatomaceous earth (DE) (0.5:3.5―2:2), conductivity, and pH values. The extraction efficiency was compared with conventional extraction methods. The results from the study indicate that the concentration of quercetin was highest under the following conditions: extraction temperature of 165℃, static time of 15 min, mixture ratio of 1.5:2.5 for onion skin and DE, conductivity of water 6.18 μS/cm, and a water pH of 6.04. The efficiency of subcritical water extraction (SWE) was compared to results obtained using ethanol, methanol, or water at boiling point. The extraction yield under the optimum condition was 16.29±0.75 mg/g onion skin, which was over eight-, six-, and fourfold higher than those obtained using the ethanol, methanol, and water-at-boiling-point extraction methods, respectively. In this study, the glycosides are converted to aglycone forms by enzymatic hydrolysis reactions using cellulcas, viscozyme, and β-glucosidase. By using specific enzyme, quercetin-4’-glucoside was converted to active quercetin aglycone that was enhanced in the yield of 29.41%. Overall results indicate that SWE is a highly efficient and rapid method for recovering a valuable bioflavonoid, quercetin, from onion skin, and an additional in-situ sterilization effect would be expected similar to that experienced using thermal retorting.;양파껍질에 많이 함유되어 있는 대표적인 플라보노이드류 중 하나인 quercetin은 식품의 산화방지제로 주로 사용되며, 항산화, 항염증, 항알레르기, 항바이러스, 항암 작용 등 다양한 기능성을 가지고 있는 것으로 알려져 있다. 본 연구에서는 추출용매로서 순수한 Milli-Q water 만을 사용하는 친환경 추출기술인 아임계 추출법 (Subcritical Water Extraction, DIONEX ASE 100)을 이용하여 양파껍질의 외피부분에서 quercetin과 배당체인 quercetin-4’-glucoside를 추출하여 분석하여 기존의 용매추출법과 추출농도를 비교하였다. Quercetin 추출을 위한 최적조건을 찾기 위하여 추출온도 (100- 190), 추출시간 (5-30분), 추출반복횟수 (1-3), 양파껍질의 크기 (<1 mm, >10 mm), 양파껍질과 규조토의 배합비율 (0.5:3.5-2:2), conductivity, 및 pH 를 독립변수로 하고 추출된 quercetin의 농도를 HPLC를 이용하여 분석한 정량값을 종속변수로 하여 실험을 설계하였다. 최대 추출농도는 165℃의 추출온도에서 15분간 양파껍질과 규조토의 배합비율을 1.5:2.5, conductivity 6.18 μS/cm, pH 6.04의 물을 용매로 하였을 때 16.29±0.75 mg/g onion skin 정도로 quercetin이 산출되었으며, 이는 일반적인 용매추출법인 메탄올추출법 (60℃, 2시간) 및 에탄올추출법 (60℃, 2시간)과 열수추출법 (100℃, 3시간)에 비해 6 - 8배 정도 높은 수치였으며 플라보노이드 추출방법의 대체기술로서 아임계 추출법의 우수성을 보여준 결과로 사료된다. 또한, 가수분해 반응으로 viscozyme 과 β-glucosidase 효소를 사용하여 quercetin 배당체를 aglycone 형태로 분해하여 더 높은 quercetin 추출률을 확인하였다.
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