Behavior of antioxidants under some cooking conditions

2002 Fiscal Year Final Research Report Summary

• Project/Area Number: 13680155
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: 食生活
• Research Institution: Osaka City University
• Principal Investigator: KIKUZAKI Hiroe Osaka City University, Graduate School of Human Life Science, Associate Professor, 大学院・生活科学研究科, 助教授 (60291598)
• Project Period (FY): 2001 – 2002
• Keywords: curry leaves / carbazole / mahanine / ginger / [6]-gingerol / antioxidant activity / heat oxidation / cooking

Research Abstract

This study was aimed to elucidate what behavior antioxidants from food showed under cooking condition. Two spices, curry leaves (the leaves of Murraya koenigii) and ginger were investigated. When dried curry leaves were added to the substrate oil including 10% methyl linoleate at 110℃, addition of only 0.1% of curry leaves was enough to delay oxidation of the substrate oil, which suggested that curry leaves could have antioxidant effect under heat-cooking condition. Curry leaves were extracted with dichloromethane and the extract was purified using repeated chromatographic techniques to isolate six compounds, which were determined to be carbazoles based on the spectroscopic evidences. Among them, three compounds each of which had a hydroxyl group on the carbazole skeleton showed a strong antioxidant activity. Especially mahanine, a major carbazole, had the strongest ability, which promoted us to elucidate its behavior under heat oxidation. During oxidation, mahanine gradually decreased . Immediately after mahanine was exhausted, oxidation of the substrate oil was progressed radically. Furthermore, there was no marhanine derivative detected which remarkably increased during oxidation. These facts suggested that mahanine was stable under heating condition and directly delayed oxidation of the oil. In the case of ginger, the behavior of [6]-gingerol, a major antioxidant of ginger, under some cooking conditions was investigated. The squeezed juice of ginger passing through 40 mesh possessed about two thirds of antioxidant capacity and [6]-gingeol contents compared with ginger before squeezing. When grated ginger was kept at room temperature for 24 hr, the antioxidant activity decreased significantly whereas [6]-gingerol content did not significantly decrease, which suggested that other antioxidants might decrease. When minced ginger was flied for 3 min, ginger maintained the antioxidant activity and [6]-gingerol content, which indicated that [6]-gingerol could be stable enough to exhibit its antioxidant effect after short dry cooking.