Abstract: This study aimed to investigate the effects of solvents with different polarities on the compositions and contents of free and bound phenolics as well as antioxidant activities in hulless barley grains. In the present study, four different solvent mixtures were used to extract free phenolic compounds from 4 varieties of hulless barley. Alkaline and acidic hydrolysis methods were compared for the hydrolysis of bound phenolic compounds from hulless barley. The phenolic compositions of the free and bound fractions were identified by high performance liquid chromatography (HPLC). The antioxidant activities were determined by 1,1-diphenyl-2- picrylhydrazyl (DPPH) and 2,2’-azinobis-(3-ethylbenzthiazoline-6-sulphonate (ABTS) radical scavenging capacity and ferric ion reducing antioxidant power (FRAP) assays. The results showed that 80% aqueous acetone extracted the largest amount of total free phenolic compounds (139.79–235.96 mg/100 g) and total free flavonoids (9.88–15.52 mg/100 g) from hulless barley of the solvents tested. The acidic hydrolysis method released 1.9–3.1 and 1.3–2.9 times more bound phenolics and flavonoids than the alkaline method. Eight to eighteen phenolic compounds were detected in the aqueous acetone extract of hulless barley, and its phenolic content was significantly higher than three other extracts. Chlorogenic acid, benzoic acid, catechin, quercetin, and rutin were identified as main free phenolic compounds. The types and amounts of bound phenolic compounds released by the acid hydrolysis method were higher than those achieved by the alkaline hydrolysis method. Gallic acid, p-coumaric, syringic acid, benzoic acid, 3, 4-dimethoxybenzoic acid, and hesperidin were found to be main bound phenolic compounds. The 80% aqueous acetone extract showed the highest DPPH (852.56–1 484.18 μmol/100 g) and ABTS+· (358.93–518.09 μmol/100 g) scavenging capacity and the highest FRAP value (1 250.55–2 041.16 μmol/100 g) of the four extracts tested. The DPPH scavenging capacity, FRAP values and ABTS+· scavenging capacity of the bound phenolic compounds obtained by acid hydrolysis were 7.6–10.3, 1.2–1.8, 1.1–1.3 folds higher than those obtained using the alkaline hydrolysis method. The free and bound phenolic contents and profiles and antioxidant activities of the extracts were found to be dependent on the extraction solvent used. Conclusively, 80% aqueous acetone and the acid hydrolysis method were suitable for extraction of free and bound phenolic compounds from hulless barley. Hulless barley exhibited high antioxidant activity and could be a potential natural source of antioxidants.

Key words: hulless barley, extraction solvents, phenolic composition, antioxidant activity