Assessment of the contributions of anthocyanins to the total antioxidant capacities of plant foods

Abstract

Anthocyanins widely distributed in plant foods have antioxidant activity and several health-beneficial effects. Anthocyanin contents and their contribution to total antioxidant capacity (TAC) of various plant foods (Angeleno plum, red plum, sour cherry, red grape, beetroot, and red cabbage) were analyzed in this study by using high-performance liquid chromatography (HPLC) and spectrophotometric methods such as pH differential, cupric reducing antioxidant capacity (CUPRAC) and 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS). The individual anthocyanin constituents of plant extracts were identified and quantified by HPLC on a C-18 column using gradient elution of mobile phase comprising MeOH-0.2 % o-phosphoric acid and photodiode array detection. Trolox equivalent antioxidant capacity (TEAC) coefficients of the studied standards by the CUPRAC assay were found in the order: cyanidin > kuromanin > keracyanin > delphinidin > pelargonidin > peonidin > malvidin > peonidin-3-glucoside in accordance with the theoretical expectations of established structure-antioxidant activity relationships. The theoretical TAC values calculated by the HPLC-CUPRAC and HPLC-ABTS methods were very close to the spectrophotometric values (95-103 %) for synthetic mixtures. These combined HPLC-spectrophotometric methods using TEAC coefficients of anthocyanins determined by CUPRAC and ABTS methods become possible to evaluate the anthocyanins contribution to TAC values of foods as well as individual anthocyanins in a single chromatographic run.