Functional antioxidant and tyrosinase inhibitory properties of extracts of Taiwanese pummelo (<i>Citrus grandis</i> Osbeck)

Abstract

In recent years, the overproduction of citrus fruits has resulted in an unnecessary increase in agricultural wastes in Taiwan. In an attempt to find an application for these potentially valuable wastes, we evaluated the antioxidant and whitening properties of six Taiwanese pummelo varieties (Miyu Shihtouyu Taipeiyu Touyu Wentan and Hsishihyu). The methanolic extract of Citrus grandis Osbeck Miyu (Miyu) had the highest phenolic content (9.99 mg of gallic acid equivalent/g). C. grandis Osbeck Shihtouyu (Shihtouyu) displayed the highest 2, 2-azino-bis-(3- ethylbenzthiazoline-6-sulfonic acid) content (9.3 mg trolox equivalent antioxidant content/g), indicating its good free radical-scavenging activity. C. grandis Osbeck Taipeiyu (Taipeiyu) showed the highest 1,1-diphenyl-2-picrylhydrazyl content and this compound too possesses good radical-scavenging activity. The ferrous-ion chelating effect of C. grandis Osbeck Touyu (Touyu) and C. grandis Osbeck Wentan (Wentan) was found to be 0.78 and 0.92 mg/ml, respectively. Taipeiyu showed the highest limonin content (1251.86 μg/ml). Touyu inhibited tyrosinase up to 90.8% (10 mg/ml), which was almost similar to the 95% inhibition shown by kojic acid (10 mg/ml). Thus, the components of pummelo have high potential for use as ingredients in products that prevent skin pigmentation. These results indicate that the methanolic extracts and the phytochemicals derived from pummelo are potential natural antioxidant agents.

Key words: Antioxidant, free radical chelating, limonin, pummelo, tyrosinase.