Effects of Superfine Grinding and High-pressure Processing on Physicochemical Properties and Polyphenol Antioxidant Activity of Barley Leaves

In this study, barley leaves were used as the main material to investigate the effects of superfine grinding (SG) and high-pressure processing (HPP) on their physicochemical properties and polyphenol antioxidant activity. The particle size, density, fluidity, morphology and structure of barley leaf powders were characterized using various methods, including the particle size analyzer, powder density tester, colorimeter, scanning electron microscope and Fourier transform infrared spectroscopy. The antioxidant activity of soluble and bound polyphenols in barley leaves was evaluated using the ABTS+ radical scavenging activity and ferric reducing antioxidant power. The results showed that, compared with ordinary grinding, SG significantly reduced the particle size, moisture content and fluidity of powders (P<0.05). The bulk density and tap density increased significantly (P<0.05). Powders with SG exhibited a brighter green color and a rougher surface. The ABTS+ radical scavenging activity and ferric reducing antioxidant power of soluble polyphenols were reduced by 42%~47% and 50%~61%, respectively. After HPP, the particle size was more uniform, and the particle surface became more porous. The color change in powders caused by HPP at 100 MPa was almost invisible to the naked eye. Importantly, the ABTS+ radical scavenging activity and ferric reducing antioxidant power of both soluble and bound polyphenols were improved obviously by HPP (P<0.05). Besides, no new chemical bonds were generated as a result of SG or HPP. In conclusion, the combined application of SG and HPP in the production of barley leaf powders results in the product with a fine and uniform particle size, bright green color, and strong polyphenol antioxidant activity.