Antioxidant activity of free and hydrolyzed phenolic compounds in soluble and insoluble dietary fibres derived from hulless barley

Phenolic compounds associated with dietary fibre are present in free, soluble conjugated and insoluble-bound forms. In this study, total soluble, free, esterified, etherified and insoluble-bound phenolic fractions were extracted from the insoluble dietary fibre (IDF) and soluble dietary fibre (SDF) of hulless barley. Total phenolic content (TPC), total flavonoid content (TFC) and antioxidant activities of five phenolic fractions of IDF and SDF were evaluated. Major phenolic acids and flavonoids were analyzed by high performance liquid chromatography. The results revealed that the TPC and TFC of five phenolic fractions of IDF were 2.42–7.33 and 3.08–10.00 times, respectively, which were higher than those in SDF. Insoluble-bound phenolic fractions had the highest TPC and TFC among the five phenolic fractions. A significant positive linear correlation between TPC and antioxidant activity was observed in each of the five phenolic fractions from IDF and SDF ( P  < 0.05). Furthermore, ferulic acid was an abundant phenolic compound in total soluble and insoluble-bound phenolic fractions among IDF and SDF. This study indicates that IDF and SDF are rich in phenolic compounds which can be considered as functional food ingredients or nutraceuticals.