Antioxidant Capacity of Different Fractions of Vegetables and Correlation with the Contents of Ascorbic Acid, Phenolics, and Flavonoids

The antioxidant capacity of different fractions of 17 vegetables were analyzed using ferric reducing antioxidant power assay (FRAP assay) after water and acetone extractions. The contents of ascorbic acid, phenolics, and flavonoids were determined and their correlations with FRAP value were investigated. The results showed that the peel or leaf fractions of vegetables were stronger than the pulp or stem fractions in antioxidant capacity based on total FRAP value. Lotus root peel was the highest and cucumber pulp the lowest in total FRAP value among the vegetable fractions analyzed. All water extracts were higher in FRAP value than the acetone extracts. The FRAP value was significantly correlated with the contents of ascorbic acid, phenolics, or flavonoids in water extracts, in which the phenolics contributed most based on multivariate regression analysis. We conclude that different vegetable fractions were remarkably different in antioxidant capacity. The phenolics are responsible mostly for the antioxidant capacity of vegetables in vitro.