Ultrasonic assisted alkali extraction of protein from defatted rice bran and properties of the protein concentrates

Alkaline extraction for the preparation of protein concentrate from rice bran was compared with a range of ultrasonic treatments. Results revealed that the extraction time decreased, and the reaction rate constant increased, with increasing ultrasonic power. The reaction rate constants were 0.0065, 0.0130, 0.0237 and 0.0924 at 40, 60, 80 and 100 W respectively. The defatted rice bran protein concentrate (DRBPC) using ultrasonication (100 W for 5 min) and conventional methods showed no significant difference in bulk densities ( P  > 0.05) but it had higher yield (%) and was lighter brown using ultrasonication ( P  ≤ 0.05). The SEM showed that the residual rice bran after extracting protein using ultrasonication exhibited more damage than the conventional method. The functional properties of both samples were not significantly different ( P  > 0.05) in terms of foam and emulsifying stability. However, the water and oil absorption, foam capacity and emulsion activity were significantly different ( P  ≤ 0.05). The nitrogen solubility index of both DRBPC samples gave similar profiles with the lowest solubility at pH 4–6.