Antioxidant and Antitumor Promoting Activities of Apple Phenolics

摘要

The antioxidant and antitumor promoting activities of major phenolic phytochemicals of apples were investigated. The contribution of each antioxidant to total antioxidant activity of apples was determined using 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) radical scavenging assay. The estimated contribution of major phenolics and vitamin C to total anitoxidant capacity of fresh apples is as follows: quercetin > epicatechin > procyanidin B2 > phloretin > chlorogenic acid > vitamin C. Recent reports suggest that carcinogenicity of hydrogen peroxide (H2O2) is attributable to the inhibition of gap-junctional intercellular communication (GJIC), which is related to tumor promotion process. The inhibition of GJIC by H2O2 was recovered effectively by the treatment of apple extracts. Among major antioxidants in apples, quercetin exerted the strongest protective effects on H2O2-induced inhibition of GJIC, following epicatechin, procyanidin B2, and vitamin C, while chlorogenic acid and phloretin did not show any effects. The results indicate that flavonoids such as quercetin, epicatechin, and procyanidin B2 contribute significantly to total antioxidant capacity and antitumor promoting activities of apples, which may contribute to a putative cancer chemopreventive activity.