Influence of Different Processing Methods on Phenols in Hulless Barley

This research was performed to investigate the impacts of different processing methods on phenols in hulless barley for the purpose of achieving furthest retention of the antioxidant and hypoglycemic bioactives. Using Hainan Kunlun 17 hulless barley as experimental material, the hulless barley grains were thermally processed by six different processing methods, including steaming, boiling, frying, microwave, baking and air fryer, and the contents of free polyphenols, bound polyphenols, free flavonoids and bound flavonoids, as well as the changes of antioxidant and hypoglycaemic activities in hulless barley before and after processing were analysed. The results showed that the contents of polyphenols and flavonoids in hulless barley were varied after preparing by different processing methods. Compared with unprocessed hulless barley, the contents of free polyphenols and free flavonoids from other processing methods were significantly decreased (P<0.05) (except frying), while the contents of bound polyphenols and bound flavonoids increased. Compared with unprocessed one, the free polyphenols content of hulless barley after steaming and boiling preparation were deeply decreased by 43.77% and 67.85%, respectively, whereas the content of bound flavonoids in the fried one was increased by 38.10%. In addition, the polyphenol extracts of the heat processed hulless barley had better scavenging ability of DPPH free radical and inhibitory activity of α-glucosidase, and the scavenging and inhibitory activities were concentration-dependent in a certain concentration range. Among the six processing methods, DPPH radical scavenging rates in free and bound polyphenol extracts (5 mg/mL) of fried hulless barley showed the highest levels of 70.01% and 54.52%, respectively, and their α-glucosidase inhibition rates were also the highest at 84.84% and 75.70%, respectively. Therefore, phenolics could be retained maximally after frying, and then exerting their antioxidant and hypoglycemic effects.