Ultrasonic-Assisted Extraction of Rice Bran Protein Using Response Surface Methodology

Rice bran was used for isolating protein through ultrasonic-assisted extraction. The protein was converted into protein hydrolysates (PH) with three commercial enzymes. The optimal condition for rice bran protein production was 76% sonication amplitude, 18 min extraction and 0.99 g/10 mL solid–liquid ratio, which gave protein yield of 4.73 ± 0.03%. The degree of hydrolysis for the rice bran protein by Subtilisin A (SPH), Actinase E (APH) and Neutrase 0.8L (NPH) was 20.03 ± 0.24%, 13.84 ± 0.04% and 5.54 ± 0.07%, respectively. The molecular weight of the isolated proteins ranged between <11 to 75 kDa. The NPH exhibited greater scavenging activity on 1,1-diphenyl-2-picryhydrazyl radical and ACE-inhibitory activities. The SPH was efficient in reducing power and metal chelating activities. In addition, NHP displayed the highest positive effect for foaming activity (66.25%), then followed by APH (57.50%) and SPH (52.50%). The results suggest that the partial hydrolyzed rice bran protein is more suitable for application in food systems rather than the non-hydrolyzed form. Practical Application: Optimizing the condition for rice bran protein extraction is desirable and practical for related plant materials. Understanding the optimal conditions is important because it could enable an extraction method that could be used instead of conventional methods that take a long time for extraction. This study also suggests some enzymes for producing rice bran protein hydrolysates (PH) that have desired properties for specific usage such as for antioxidant activities and/or functional properties. The method for producing PH and controlling the degree of hydrolysis could be promptly applied.