Black Rice Anthocyanins as An Effective Antioxidant of Inhibition of Oil Oxidative Based on Molecular Modification.

ABSTRACT

This present work investigated the influence of black rice anthocyanins as antioxidants on the oxidation stability of oil. Malonic acid, succinic acid and succinic anhydride were grafted on black rice anthocyanins through acylation method to improve their antioxidant activity in oil. The results from fourier transform infrared spectroscopy (FTIR) showed new absorption peaks near 1744 cm -1 and 1514 cm -1 , which implied that malonic acid, succinic acid and succinic anhydride grafted on the -OH of glucoside and rutinoside through esterification reaction and resulted that the polarity of these were reduced. Total content of anthocyanin (TAC) decreased to 166. 3 mg/g, 163.7 mg/g and 150.2 mg/g, respectively after modification with succinic acid, malonic acid and succinic anhydride. Compared with native anthocyanins, the acylation of black rice anthocyanins partially reduced its antioxidant activity. In addition, DPPH clearance of molecular modified anthocyanins decreased to 62.6% (San-An). As revealed in the oil stability through the determination of primary oxidation products (PV) and secondary oxidation products (p-AV), Sa-An, Ma-An and San-An showed stronger antioxidant activity in Schaal oven accelerated oxidation test during 12 days than native black rice anthocyanin in both corn oil and flaxseed oil. Molecular modified black rice anthocyanins are expected to be used as colorants, antioxidants, etc. in oil-rich food.