Improving yield, functional properties, and aroma profile of rice bran protein through innovative extraction and precipitation methods

Rice bran is a milling byproduct and rice bran protein (RBP) is a promising source of plant-based protein. This study investigated the impact of alkaline and acid extractions followed by isoelectric point (IEP) and heat coagulation precipitations on the quality and functionalities of RBP. Alkaline extraction, followed by IEP and heat coagulation, showed the highest protein recovery of 48.77%, which is double that of conventional alkaline extraction and IEP. The FTIR data showed that β-sheet and α-helix content reduced; however, random coil and β-turn increased by acid and heat addition. Addition of heat coagulation to IEP after alkaline extraction increased solubility from 62.94% to 94.74%. However, the emulsification and surface hydrophobicity were decreased during heat and acid-assisted extraction. The in-vitro digestibility was the highest at 83.57% in alkaline-acid extraction, followed by heat and IEP. The aroma profile of RBP shows a complex mixture of ethanol-2-butoxy, 2-methyl-4-vinyl-phenol, 2,4—heptagonal, (E,E)-, Undecane, and 5-methyl to form a typical flavor with waxy and rancid undernotes. The total amount of volatile compounds in conventional extraction was 1.97 μg/g, while alkaline-acid extraction with IEP had only 0.87 μg/g. The RBP from alkaline-acid extraction with IEP showed the least volatile compounds and most neutral proteins.