Phenolic acid composition and antioxidant capacity of acid and alkali hydrolysed wheat bran fractions

Phenolic acid concentrations, profiles and antioxidant capacity of acid and alkali hydrolysates from the bran of six wheat cultivars representing six Canadian market classes were determined. Aqueous ethanol was used to extract the free phenolics (FP) and diethyl ether to extract the insoluble bound phenolics released after acid and alkaline hydrolysis of the bran. Folin–Ciocalteu (FC) reagent was used to estimate the total phenolic content and HPLC-UV to detect and quantitate 14 phenolic acids and one lignan. trans-Ferulic acid was the dominant acid in the bran extracts but mass spectrometric analysis showed tryptophan to be dominant in the FP extracts. The antioxidant capacity of individual phenolic acids and extracts was assessed using 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS), and 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox) equivalent antioxidant assays. The FP extracts had the lowest average antioxidant capacity and the hydrolysates the highest. Based on the concentration of each phenolic acid in the extracts, and the antioxidant capability of each phenolic standard, trans-ferulic acid was the dominant contributor (66.4–95.5%) to antioxidant capacity of the wheat bran extract.