Abstract
The antioxidant activities of hot-water extracts of 15 kinds of commercial tea were compared. The antioxidant components of banaba tea (Lagerstroemia speciosa) were identified, and their antioxidant activities were assessed. Antioxidant activities were determined by Rancimat analysis for evaluation of induction time (IT rancid point), DPPH radical and superoxide scavenging activity. Polyphenols in banaba tea were identified by preparative thin-layer chromatography and high-performance liquid chromatography. The antioxidant activity decreased in the order maidenhair>rooibosh>green>mugwart>banaba>hydrangea>Japanese persimmon>loquat>houttumia heb>taheebo teas. In perticular, maidenhair, rooibosh, and green teas showed higher antioxidant effects than the others. On the other hand, aloe perrye and rose moschata teas had no preventive effect against oxidative deterioration of oil. This preventive effect increased in proportion to the dose for green, barley and maidenhair teas, but persimmon and loquat teas had no antioxidant effect at concentrations below 0.1%. The order of DPPH scavenging activity was gallic acid>green tea>banaba tea. A large number of peaks in the ethyl acetate extract obtained from banaba tea were isolated by HPLC, and identified as gentisic and gallic acids, catechin, and resorcinol. The main polyphenol components were gallic and gentisic acids and catechol. Among the detected polyphenols, gentisic, and gallic acids had the greatest preventive effect against oxidative deterioration of oil.
