Abstract: The hexane, ethyl acetate and methanol extracts of Tibetan hull-less barley (THB) bran displayed dose-dependent inhibitory activities on α-glucosidase in vitro. The hexane and ethyl acetate extracts had higher inhibitory activities than did acarbose, which is used in clinical treatment of type 2 diabetes. Gas chromatography-mass spectrometry (GC-MS) analysis showed that linoleic acid, oleic acid, palmitic acid and α-linoleic acid were the main fatty acids in the hexane extracts, accounting for 96.5% of the total fatty acids. All of these four fatty acids have been reported to be potent inhibitors of α-glucosidase. Moreover, 65 peaks were separated from the unsaponifiable fractions, with 17 of them identified as sterols, triterpenes and long chain fatty alcohols, respectively. The total free phtosterol content was 7 357.72 mg/kg, which presented β-sitosterol, campesterol, desmosterol, stigmasterol, and fucosterol as the primary phytosterols. In addition, β-sitosterol and campesterol accounted for 83% of the total phtosterols. These results show that THB can be a natural source of potent α-glucosidase inhibitors.

Key words: Tibetan hull-less barley bran, α-glucosidase inhibitors, gas chromatography-mass spectrometry (GC-MS), fatty acid, unsaponifiable matters