Abstract: In this study, total soluble, free, esterified, etherified and insoluble bound polyphenols were extracted and separated from ‘Changhei’ hulless barley kernels. The contents of polyphenol and flavonoids and antioxidant activities in vitro were determined. Moreover, the composition of phenolic compounds was quantitatively and qualitatively analyzed by high performance liquid chromatography (HPLC). The results showed that the polyphenol contents of the total soluble, free, esterified, etherified and insoluble bound polyphenol-rich extracts ranged from (1.97 ± 0.06) to (16.97 ± 0.25) μmol/g and the flavonoids contents from (0.14 ± 0.04) to (1.08 ± 0.11) μmol/g. The contents of polyphenols and flavonoids in the total soluble polyphenol-rich extract were significantly higher than those in the other four polyphenol-rich extracts, and insoluble bound polyphenols were significantly more abundant than free, esterified and etherified polyphenols (P < 0.05). The ferric reducing antioxidant power, 1,1-diphenyl-2-picrylhydrazyl radical scavenging activity and Trolox equivalent antioxidant capacity of the total soluble polyphenols were the highest among the 5 polyphenols, and the insoluble bound polyphenols were significantly stronger antioxidants than the free, esterified and etherified polyphenols. Similarly, the hydrogen peroxide scavenging activity of the insoluble bound polyphenols was significantly higher than that of the other four polyphenols (P < 0.05). There was a significantly positive correlation between the polyphenol contents and the antioxidant activity (R2 = 0.880–0.998). A total of 18 phenolic compounds were identified including hydroxybenzoic acid, hydroxycinnamic acid and flavonoids, with protocatechuic acid, ferulic acid and catechin being the most abundant ones. It can be concluded that hulless barley, with abundant phenolic compounds, can be regarded as a potential antioxidant value-added functional food ingredient.

Key words: ‘Changhei’ hulless barley, phenolic compounds, antioxidant activity