Plant-derived proteins are playing an increasingly important role in dietary supplementation and food processing. Rice protein powder has unique hypoallergenic properties, and the hydrolyzed polypeptide has health-care effects such as lowering blood pressure and cholesterol. In the following, the separation and extraction techniques of rice protein, such as alkaline extraction, acid precipitation and enzymatic methods, are described in detail.
1. Alkaline extraction and acid precipitation
Alkaline extraction of rice protein is a more common and traditional method at present, which utilizes the principle that rice protein contains more than 80% of alkali-soluble protein. The protein obtained by alkali extraction is of high purity, but in the extraction process, the extraction rate and physical and chemical properties of rice protein are affected to a certain extent due to the use of a higher concentration of alkali solution.
Using alkaline extraction and acid precipitation to extract rice protein, more protein components can be obtained under optimal conditions. The alkaline extraction process is simple, but the consumption of water and alkali is large, so it is difficult to apply the alkaline extraction to industrial production.
2. Enzymatic method
Enzymatic extraction can be divided into protease extraction and non-protease extraction. The protease extraction method uses related enzymes to degrade and modify rice protein. This allows the rice protein to be extracted into soluble peptides. Common proteases include neutral protease, alkaline protease, composite protease, etc. Among them, alkaline protease has the best extraction effect.
3. Physical aid method
Physically assisted extraction generally uses physical means such as ultrasonic, freeze-thaw, high pressure and high-speed homogenization to assist in the extraction of protein from rice by alkaline or enzymatic methods. The advantage of physical-assisted extraction method is that it can improve the extraction rate of rice protein.
1). Ultrasonic-assisted extraction is to use the cavitation, mechanical effect and thermal effect of sound waves to improve the speed and frequency of the movement of the material molecules in the extractant. Solvent molecules penetrate the extract cells faster and easier, allowing the target substance to dissolve faster.
2). The principle of freeze-thaw is that when repeated freezing and thawing, the water in the cells will form ice crystals, and the salt concentration in the remaining liquid will increase, which will cause the cells to swell and rupture the cell wall, and the rice protein is more easily dissolved.
3). The high-pressure assisted extraction method is that when the pressure reaches a certain level, the complex chemical bonds between starch and protein in the rice are broken, and the quaternary structure of the protein is changed, thereby improving the extraction rate of rice protein.
4). High-speed homogenization is the use of high-speed shearing, high-frequency oscillation, cavitation, convective impact and other mechanical forces and corresponding thermal effects when the material passes through the homogenizing cavity quickly. The resulting mechanical force and chemical effect can induce changes in the physical, chemical and structural properties of the material macromolecules, and finally achieve the effect of improving the protein extraction rate.
Summary
With the deepening of research and the intervention of high-tech, the extraction rate and functional properties of rice protein will also be improved. The development and utilization of rice protein powder will surely achieve greater economic and social benefits.
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