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Mechanism and kinetics for singlet oxygen quenching activities of six different catechins in the methylene blue sensitized photo oxidation of linoleic acid
3rd International Conference and Exhibition on Food Processing & Technology
July 21-23, 2014 Hampton Inn Tropicana, Las Vegas, USA
Mun Yhung Jung
Accepted Abstracts: J Food Process Technol
Abstract:
The protective activities of different catechins on the singlet oxygen induced photooxidation of linoleic acid were studied. The protective activities were in order of epigallocatechin gallate (EGCG) = epigallocatechin (EGC) > gallocatechin gallate (GCG) > epicatechin gallate (ECG) > epicatechin (EC) > catechin (C). EGCG showed significantly stronger antioxidative activity than α-tocopherol at the later oxidation stage (p<0.05) due to the higher stability of EGCG. Unlike α-tocopherol, green tea catechins possessed strong antioxidative activity even at the later oxidation stage. Electron spin resonance (ESR) spectroscopy and visible-spectroscopic data showed unambiguous evidences that the protective activity of green tea catechins against the photosensitized oxidation of linoleic acid was due to the singlet oxygen quenching mechanism. The total singlet oxygen quenching activities (kr+kq) in the same system were calculated by using a Stern-Volmer plot. The kr+kq values of EGCG and C were 1.31x108 and 1.66x107 M-1sec-1, respectively. The pyrogallol (B) ring structure was the most influencing factor for the kr+kq values. Stereospecific configuration also provided a considerable influence on the values. The G-ring structure did not show significant influence in the value for EGCG and EGC. The kr values of the catechins were 3.23 x105 - 1.64 x106 M-1sec-1. Overall, green tea catechins were better antioxidant than α-tocopherol for the protection of linoleic acid from singlet oxygen oxidation. The result also unambiguously explained the mechanism of how catechins protect nutrients in food system, and the tissues and cells from the damages in biological systems against the singlet oxygen oxidation.