Determination of free and bound phenolic acids, and evaluation of antioxidant activities and total polyphenolic contents in selected pearled barley

Abstract

The content of insoluble bound phenolic acids in pearled barley was determined by an analytical system consisting of alkaline hydrolysis extraction, high-performance liquid chromatographic separation and electrochemical detection. Insoluble bound phenolic acids in five pearled cultivars and fifteen breeding lines of barley comprised ferulic acid (4.3-34.2 mg/100 g dry matter), sinapic acid (0.025-0.445 mg/100 g), caffeic acid (0.002-0.016 mg/100 g). Soluble free polyphenols comprised procyanidins (12.2-80.3 mg/100 g), catechin (0.1-28.2 mg/100 g), and total pholyphenol comprised 152.4-324.0 mg-gallic acid equivalents/100 g. The 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity for the barley samples ranged from 403 to 1501 μmol-Trolox equivalents/100 g whereas those of oxygen radical absorbance capacity (ORAC) ranged from 1050 to 3816 μmol-Trolox equivalents/100 g. High correlation (0.980, p<0.01) was found between the DPPH and ORAC assays. Total polyphenol contents positively correlated with the DPPH (0.875, p<0.01) and ORAC (0.881, p<0.01) assays. The correlation coefficient between insoluble bound phenolic acids and total polyphenol contents was higher than that between soluble free polyphenols and total polyphenol contents. Taken together, the insoluble bound phenolic acids appear to greately contributed to the antioxidant activity in pearled barley.