pH shifting treatment of ultrasonically extracted soybean meal protein isolate: Effect on functional, structural, morphological and thermal properties

Soybean meal, an agro-industrial by-product is rich in protein and can be used as a potential source of protein isolate. In the present work, protein isolate was extracted from soybean meal by ultrasound treatment and pH was adjusted to 2, 4, 6, 8, and 10. Ultrasonic extraction of protein isolates resulted in maximum yield and purity of 41 ± 2 % and 92 ± 2% respectively at optimized ultrasound conditions. Soybean meal protein isolates adjusted at pH 10 showed reduced particle size, increased solubility, high emulsifying, foaming, water, and oil binding properties. Structural characteristics of pH adjusted soybean meal protein isolate studied by FTIR and XRD indicated increased changes of secondary structures and less crystallinity of protein after pH adjustment. SEM and TEM analysis indicated the formation of a more aggregated structure of protein in pH adjusted samples compared to the control. The soybean meal protein isolates sample adjusted at pH 10 showed higher thermal stability with a denaturation temperature of 123 ± 2 °C as compared to those samples adjusted pH at 2, 4, 6, and 8. Thus, pH adjustment can be adopted as a potential method for the improvement of soybean meal protein and increase its applicability in a wide range of food product development. • Different pH shifting (4−10) treatments were given to the ultrasonically obtained soybean meal protein isolate (SMPI). • SMPI obtained by shifting pH at 10 showed the highest solubility and lowest particle size. • Functional and structural properties showed significant improvement when the pH of SMPI shifted at 10. • Thermal stability was found higher in SMPI obtained by shifting pH at 10.