Saccharomyces cerevisiae and Lactiplantibacillus plantarum fermentation combined with long-wavelength ultraviolet irradiation effectively improved the physicochemical and functional properties of okara insoluble dietary fiber

Okara insoluble dietary fiber (IDF) is rough and difficult to digest, which limits its resource utilization in foods. The effects of long-wavelength ultraviolet irradiation and microbial fermentation on the structure, physicochemical and functional properties of okara IDF were evaluated. The results indicated that a single modification technique on IDF is limited and combined use of long-wavelength ultraviolet irradiation and microbial fermentation could partially disrupt the crystal structure of IDF, leading to the degradation of some functional groups of cellulose and lignin. The looser structure and change in functional groups significantly increased the water and oil holding capacity, antioxidant capacity, cholesterol adsorption capacity, sodium cholate adsorption capacity, and glucose adsorption capacity of okara IDF. Particularly, okara IDF was firstly subjected to S. cerevisiae and L. plantarum mix-fermentation and then long-wavelength ultraviolet irradiation was the most effective technology for improving the physicochemical characteristics and functional properties of okara IDF and the adsorption capacities for cholesterol, sodium cholate and glucose of MU-IDF is 19.83, 5.42 and 16.47 mg/g, respectively, which are 1.57, 4.50, and 2.44 times higher than those of untreated IDF. • Microbial fermentation and UV-A irradiation could improve okara IDF properties. • Combination processing partially disrupted the crystal structure of okara IDF. • Changes in looser structure and functional groups increased the properties of IDF. • Microbial fermentation followed UV-A irradiation was the most effective method.