Critical evaluation of the functionality of soy protein isolates obtained from different raw materials

The objectives of the present study were to assess how structural and gelation properties of soy protein isolates (SPIs) are affected by the characteristics of the soybean meal starting material used for protein extraction. The different degree of denaturation and aggregation due to processing treatments undergone by the soybean meals significantly affect the soy protein structural organization and functional properties. The main type of interaction responsible for the aggregates differed in the commercial and laboratory isolates, thus impacting on the protein composition of the soluble fraction of the different isolates. Spectroscopy analysis revealed that the commercial SPIs differ from the lab samples essentially due to the degree of protein aggregation and to differences in the tertiary structure (amide II). At the structural level, the lab-prepared SPIs obtained from the raw soy meal subjected to more extensive processing treatments is the one closest to the commercial samples, differentiating itself from the other laboratory isolates by the aggregation state. However, some extent of pre-denaturation may be beneficial for the gelation performance of the soy protein samples, decreasing the gelation temperature and producing gels with higher stiffness and elastic character. On the contrary, extensive protein denaturation originate thermodynamically stable aggregates, water insoluble macro-aggregates less unfolded and dissociated by the heat treatment, being less available to integrate the three-dimensional network.