Effects of Physical Modification Methods on Physicochemical, Structural and Functional Characteristics of Insoluble...

Physical treatment can improve the quality and overall characteristics of insoluble dietary fiber (IDF). This study investigated the effects of microjet homogenization treatment (MT), ultra-high-pressure treatment (HP), and ultrasonic treatment (UT) on the compositional profile, microstructure, basic properties, and bioactivity of IDF from okara. The modification processes increased IDF yield (unmodified IDF: 65.55%; MT-IDF: 70.51%; HP-IDF: 75.29%; UT-IDF: 79.09%). The mechanical action disrupted the compact structure, refined the particles, and increased the specific surface area (SSA). Compared with unmodified IDF (0.18 m²/g), the SSA values of MT-IDF, HP-IDF and UT-IDF increased by 83.33%, 50.00%, and 72.22%, respectively, thereby improving the overall hydration characteristics and adsorption performance of IDF. UT-IDF exhibited excellent water-holding capacity (8.11 g/g), yet its thermal stability ((mass loss: unmodified IDF (36.50%), MT-IDF (23.59%), HP-IDF (26.11%), and UT-IDF (33.74%)) and rheological properties (shear rate range of 35-40 s^-1: unmodified IDF (1.77 Pa·s), MT-IDF (15.86 Pa·s), HP-IDF (21.11 Pa·s), UT-IDF (5.36 Pa·s)) were relatively inferior to those of MT-IDF and HP-IDF. Notably, MT-IDF exhibited superior modification effects, including a loose, porous microstructure, enhanced adsorption performance, and favorable prebiotic potential (Lactobacillus acidophilus 36h-OD₆₀₀: 0.594; Bifidobacterium longum 36h-OD₆₀₀: 0.509). Among the three physical modification methods, MT offers significant advantages in enhancing the quality of IDF from okara, improving its processing suitability, and facilitating its high-value utilization. However, this study still has certain limitations: the evaluation of the correlation between fiber digestion rate and probiotic potential was based only on in vitro models and has not been systematically evaluated using real food matrices.