Thermal aggregation behavior and gelation properties of core region of soy β-conglycinin.

Soy protein is widely used in plant-based foods; however, heating often induces large and irregular aggregates that compromise sensory quality. A distinct thermal aggregation behavior was observed in soy β-conglycinin (7S), contributing to soluble aggregates with limited size and minor sensory impacts. In this study, the mechanism of thermal limited aggregation in 7S was revealed by focusing on the effects of its main fractions, N-terminal extension region (ER) and core region (CR). Their evolutions in turbidity, solubility and dynamic light scattering, and conformational transition during heating were investigated. It was found that thermal limited aggregation was absent in CR which had ER removed from 7S. Its protein chains unfolded, followed by folding between molecules, leading to a nucleation process and subsequent formation of large aggregates with high packing density (1.18 g/mL at 100 °C) and hardness (353.75 MPa at 100 °C). The presence of ER showed an essential role in thermal limited aggregation of 7S. It was considered that the soft and highly charged ER could provide strong electrostatic repulsion to overcome hydrophobic interaction and prevent intermolecular aggregation of 7S. These different thermal aggregation behaviors between 7S and CR resulted in distinct gelation properties, with 7S gel exhibiting a fine-stranded network with better extensibility and water holding capacity (WHC, 99.81 %), whereas CR gel showed a coarse-aggregated and ruptured network with poor WHC (62.70 %). The theoretical insights into thermal aggregation and gelation of soy protein can provide guidelines for thermal processing of proteins and contribute to quality improvement in plant-based foods.