Optimization of protein extraction system and protein functionalities for heat-stabilized defatted rice bran.

摘要

Four studies with physical and enzymatic methods were conducted to maximize protein extraction from heat-stabilized defatted rice bran (HDRB) and to evaluate protein functionalities of the final protein products.; The first study showed that freeze-thaw, sonication, high-speed blending, and high-pressure extracted 12.0%, 15.0%, 16.0% and 11.0% protein, respectively. Sonication of 0–100% 750W with amylase or amylase and protease extracted 25.6–33.9% or 54.0–57.8% protein. Blending followed with amylase and/or protease extracted approximately 5.0% more protein. High-pressures of 0–800 MPa, with water or amylase-protease combination, extracted 10.5–11.1% and 61.8–66.6% protein, respectively.; In the second and third studies, amylase and combinations of carbohydrases and proteases significantly increased the extracted protein. Combination of pectinase and protease extracted 80% protein. Surface methodology showed that the theoretical conditions for maximum protein extraction from pectinase and protease were: water to bran ratio 20:1, pH 3.55, 3346.3 units/10 g bran, and 59.8°C for 4.33 h; and the residue treated with water to bran ratio 20:1, pH 10, 22138 units/10 g bran, 45°C, and time 3.1 h. Using these conditions, a total of 89.6% protein was extracted. Since proteins in this product were extensively hydrolyzed and the iso-electrically precipitated dried products contained only 37% protein, the products from the procedure with 80% extracted protein was used for physicochemical properties and functionality evaluation in the final study.; The final study showed that the protein molecular sizes were 6.5–66.2 kDa for freeze (FD-RBP) and spray dried (SD-RBP) protein products. The two products contained essential amino acids that can meet children's requirement. Their denaturation temperatures were 84.1 and 84.6°C, and enthalpies were 2.5 and 2.37 J/g; hydrophobicities were 20677 and 22611; the maximum solubility were 66.3 and 66.1% at pH 12; emulsifying capacities were 0.19 and 0.18, and stabilities were 16.5 and 17.3 min; foaming capacities were 4.0 ml and 4.2 ml and forming stabilities were negligible.; These results demonstrated that protein extraction by physical processes is limited. The combined use of pectinase and protease extracted over 80% protein from HDRB. The extracted protein products can find applications as nutritional ingredients and in a variety of emulsified food products.