Effect of superfine grinding on physicochemical and antioxidant properties of soybean residue powder

Soybean residue is an underutilized, nutrient-rich by-product of soybean processing. To enhance its value, we subjected soybean residue to superfine grinding and measured the resulting physiochemical properties and antioxidant activities. We prepared powders with particle sizes of 115.35, 77.93, 39.38, 25.01, and 20.44 mu m. As particle size decreased, the surface area (from 96.46 to 198.32 m(2)/kg) and swelling capacity (from 2.05 to 10.62 ml/g) increased. Conversely, we observed decreases in the surface-number mean (from 23.07 to 11.20 mu m), volume-surface mean (from 141.70 to 27.96 mu m), angles of repose (from 48.30 degrees to 31.46 degrees), water holding capacity (from 7.86 to 4.39 g/g), and oil binding capacity (from 1.78 to 1.42 g/g). The water solubility index and antioxidant activity (reducing power and free radical scavenging activities of 2,2-diphenyl-1-picrylhydrazyl and 2,2 '-azino-di-(3-ethylbenzthiazoline sulfonic acid)) improved as particle size decreased. In conclusion, superfine grinding improved some properties of soybean residue. Additionally, our findings provide theoretical support for using superfine grinding in industrial food applications.