Effects of combined fermentation and ultrasonic treatments on the structure and properties of Okara soluble dietary fiber

In this study, okara dietary fiber samples were prepared through a combination of solid-state fermentation using Aspergillus oryzae and ultrasonication. Subsequent infrared and UV–visible spectral analyses revealed that such treatment resulted in an increase in the oligosaccharide content of these samples through the enhanced cleavage of hydrogen bonds. Scanning electron microscopy and X-ray evaluation further confirmed the changes in the structural makeup of these okara SDF (soluble dietary fiber) samples relative to control samples. Following combination treatment, the soluble dietary fiber levels in these samples were three times higher than in control samples at 18.06 g/100 g. This treatment also led to a significant increase in the water holding, oil holding, and swelling capacities of the prepared fiber samples, whereas the capacity for water retention was slightly reduced. Ultrasonication alone failed to impact SDF oil holding capacity, nor did it impact cholesterol absorption at a pH of 2 used to simulate the stomach microenvironment. Together, these data thus offer a valuable reference for further work aimed at extracting soluble dietary fiber from okara.