Effect of processing on the release of phenolic compounds and antioxidant activity during in vitro digestion of hulless barley

Abstract Hulless barley is rich in phenolic compounds and has good antioxidant activity. To clarify the effects of processing and in vitro digestion on the release of phenolic compounds, we studied the phenolic components and antioxidant activity of hulless barley after steaming, roasting, and in vitro digestion. Both the total phenolic content (TPC) and total flavonoid content (TFC) in raw hulless barley (5.99 mg/g DW and 0.71 mg/g DW, respectively) were high, and furthermore, chrysoeriol-7-O-glucouronide (412.13 µg/g DW) was detected for the first time in hulless barley. Combined with the TPC and TFC of undigested group and total released content obtained from each phase in digested group, it suggested that roasting may be a better processing method than steaming. In vitro digestion significantly released far more bound phenols (ferulic acid) but hydrolysed some polyphenols (luteolin). The total released content of phenolic compounds obtained from each phase after digestion reached 46% and 45% for steaming and roasting, which was higher than in the raw product (41%). This study also showed that ferulic acid, chrysoeriol-7-O-glucouronide, luteolin, chrysoeriol, and luteolin-7-O-glucouronide contributed to the antioxidant activities. Roasting can thus be considered as a better daily thermal treatment for hulless barley than steaming in terms of natural antioxidants, and the steaming process should be closely monitored.