Effect of pH‐shifting treatment on the structural characteristics and nutritional quality of the ultrasonically extracted protein isolate from soybean meal

Abstract

Soybean meal is an underutilized byproduct of the soybean oil processing industry, which is rich in high quality protein but mostly used as an animal feed. Valorization of soybean meal on a large scale is possible by extracting protein isolate and modifying its structural characteristics through pH‐shifting or ultrasonic treatment, which has a direct association with the better functional properties of protein isolate. The present study aimed to evaluate the impact of pH‐shifting treatment on the structural characteristics and nutritional quality of ultrasonically extracted soybean meal protein isolate (SMPI). The results showed that the pH shifted SMPI had higher hydrophobicity (60.5–104.3) and free sulfhydryl group (22.67–24.45 μmol/g) than without pH shifted SMPI (53.5 and 19.67 μmol/g, respectively). The fluorescence intensity of the SMPI treated at extreme acidic and alkaline pH was higher than that of other pH‐treated samples. The ꞵ‐sheet (39.68%) components of SMPI treated at pH 10 showed the highest value when compared to other pH‐treated (38.18–39.26%). The alkaline pH‐treated sample had higher concentration of essential amino acids (36.16 g/100 g) than other acidic or near neutral pH‐treated sample (30.06–32.30 g/100 g). The quality parameters such as biological value (67.62), and amino acid index (72.77) were higher for the SMPI treated at pH 10 as compared to the SMPI treated at other pH conditions. Hence, the pH‐treatment method can be utilized as an effective technique to improve the characteristics of SMPI, which will increases its applications in various food sectors.Practical ApplicationsThe current investigation demonstrated that pH‐shifting treatment had a substantial impact on the structural and nutritional quality of the soybean meal protein isolate extracted by ultrasonication. Improvements in soybean meal protein's surface hydrophobicity, free sulfhydryl groups, and secondary structural components will expand its uses in the dairy, bread, meat, and infant food development industries, among other food sectors as these structural changes improve the functionality of protein. Furthermore, the treatment of soybean meal protein isolate with pH shifting led to a considerable increase in nutritional quality, as measured by the essential amino acid composition, essential amino acid index, and protein efficiency ratio, which is expected to increase its utilization in novel food product development.