| Abstract
| - Tea catechins showed different trends in relative antioxidant activityin different lipid systems. Incorn oil triglycerides oxidized at 50 °C, epigallocatechin (EGC),epigallocatechin gallate (EGCG),and epicatechin gallate (ECG) were better antioxidants than epicatechin(EC) and catechin at 140μM. Used as reference compounds, gallic acid (GA) was moreactive than propyl gallate (PG), andboth were more effective than EC and catechin. However, in thecorresponding corn oil-in-wateremulsions, all tea catechins, GA, and PG were prooxidants at 5 and 20μM by acceleratinghydroperoxide and hexanal formation. In contrast, in soy lecithinliposomes oxidized at 50 °C, EGCGand PG were the best antioxidants, followed by EC, EGC, ECG, catechin,and GA at 20 μM. Inliposomes oxidized at 37 °C with 10 μM cupric acetate, catechin andEC were better antioxidantsthan ECG, but EGCG, EGC, PG, and GA promoted lipid oxidation. Theimproved antioxidant activityobserved for tea catechins in liposomes compared to emulsions can beexplained by the greateraffinity of the polar catechins toward the polar surface of thelecithin bilayers, thus affording betterprotection. The marked variation in activity among tea catechinsmay be partly explained by theirdifferent reducing potentials, stabilities, and relative partitionsbetween phases in different lipidsystems. Keywords: Antioxidants; prooxidants, tea catechins; catechin; epicatechin;epicatechin gallate;epigallocatechin; epigallocatechin gallate; gallic acid; propylgallate; triglycerides; emulsion; liposome;antioxidant mechanism; interfacial oxidation; hydroperoxides;hexanal
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