Water-Holding Capacity Regulation of Dietary Fibers in Soybean Residue: From Modification Strategies, to Function Improvement and Food Texture Optimization

Abstract

Soybean residue (okara) is rich in dietary fiber (DF) (50%–60%), predominantly insoluble (>95%) with minimal soluble fiber, resulting in poor water-holding capacity (WHC, 7–8 g/g, centrifugation method). This restricts its functional properties (e.g., water absorption, water retention, adsorption, and cross-linking) and applications. WHC arises from synergistic effects of chemical adsorption, physical entrapment, and gel network formation, influenced by intrinsic factors (e.g., chemical structure, physical morphology) and extrinsic conditions (e.g., pH, temperature). This review provides a comprehensive overview of WHC in DF, including structural bases, functions, and enhancement mechanisms. It discusses various physical, chemical, biological, and combined modification strategies (physical–chemical, chemical–biological, physical–biological, and triple-synergistic) to enhance WHC by increasing surface area and porosity, restructuring fiber morphology, and introducing water-retention functional groups. These improvements not only enhance WHC but also optimize food texture, promoting functional foods development. Using soybean residue DF as a model, this review explores the relationships between modification strategies and WHC-related functionalities, as well as the applications in various food systems, including meat, bakery, and dairy products. Furthermore, it outlines key technical challenges such as the risk of reagent residues in chemical modification and the long cycle/high cost of biological modification and suggests future research directions, including the establishment of structure-activity relationship models and optimization of modification processes. Ultimately, this review aims to support the developments of soybean residue DF-derived ingredients with high WHC, optimized texture, and enriched fiber, thereby advancing the high-value utilization of soybean residue resources.