Heat Treatment Modulates Structure, Functionality, and Digestion-Related Antioxidant Activity of Xanthoceras sorbifolium Seed Meal Protein

Enhancing plant protein structure, functionality, and digestion-associated bioactivity is pivotal to advancing sustainable food applications. In this study, a controlled thermal treatment was applied to Xanthoceras sorbifolium seed meal protein (XSMP) to characterize alterations in structural features, functional performance, and digestion-related bioactivity. Structural analyses showed that moderate heating induced partial unfolding and disaggregation, leading to reduced particle size and improved colloidal stability, with optimal performance observed at 65 °C. Accordingly, foaming capacity and emulsifying activity index reached their highest values under moderate heat pretreatment (71.43% and 27.21 m2/g, respectively). Simulated in vitro gastrointestinal digestion revealed that moderate heat pretreatment enhanced protease accessibility and was associated with increased formation of low-molecular-weight fragments. As a result, digestion products from optimally treated XSMP exhibited significantly enhanced antioxidant activities during the intestinal phase, including higher reducing power, Fe2+-chelating capacity (up to 51.21%), and lipid peroxidation inhibition (82.83%). In contrast, insufficient unfolding at lower temperatures or excessive aggregation at higher temperatures reduced the susceptibility to digestive proteases and the associated functional performance. These findings demonstrate that controlled heat treatment provides a simple and eco-friendly strategy to enhance the functional potential of XSMP, supporting its application as a functional protein ingredient.