Physicochemical, Functional and Rheological Properties of Soy Protein Isolates Prepared with Various Iranian Soybean Cultivars

Soybeans, a prominent legume, offer substantial health benefits due to their rich and beneficial nutritional profile. However, the food sector requires improved protein functions. The functional and physicochemical characteristics of isolates from four widely grown soybean cultivars in Iran, namely Katul, Sahar, Tellar, and Sari, were examined in this research. The proximate analysis revealed significant differences (p<0.05) among the cultivars in moisture, ash, protein, and fat contents, with Katul isolates showing the highest protein (90.75%) and lowest fat (3.67%) content. Color analysis indicated significant variations in brightness (L*), with Katul isolates being the brightest due to lower fat and ash content. Surface hydrophobicity varied significantly among cultivars, with Sahar showing the highest value (360.30 a.u.). Protein solubility was highest for Katul protein isolate (69.43%), influencing functional properties like emulsification and foaming. Cultivar-specific differences were observed in both water absorption capacity (WAC) and oil absorption capacity (OAC), with Tellar exhibiting the highest OAC (2.42 g/mL). Emulsifying properties, evaluated through emulsion stability (ES) and emulsion capacity (EC), were highest for Sari and Katul protein isolates. Foaming properties varied significantly among the samples, so that Katul protein isolate exhibiting the highest foaming capacity (180.50%) and foaming stability (66.3%), likely attributed to its high protein content. Rheological analyses revealed that Katul had the highest consistency index (K) and shear-thinning properties, while Sahar exhibited a more Newtonian-like flow behavior. Gelation studies identified Katul as the most efficient, with the lowest gelling concentration (10%), compared to Sahar’s highest value (14%). These findings demonstrate the effect of soybean cultivar on the compositional and functional characteristics of protein isolates, suggesting potential applications in various food products depending on desired functional characteristics.