Soluble dietary fibers from black soybean hulls: Physical and enzymatic modification, structure, physical properties, and cholesterol binding capacity.

We used ultrasound-microwave comodification and enzyme modification (cellulase and hemicellulase) methods to extract soluble dietary fibers (SDFs) from black soybean hulls. Moreover, the structure, physical, and chemical properties, as well as the cholesterol-binding capacity of SDFs before and after modification were analyzed. The average molecular weight of SDFs extracted from raw black soybean hulls was 2.815 × 105  Da. By comparison, the average molecular weight of SDFs from ultrasound-microwave comodified hulls and enzyme-modified hulls decreased by 33.21% and 45.29%, respectively. The water-holding capacity (WHC), water-swelling capacity (WSC), and oil-holding capacity (OHC) of the extracted SDFs modified by the ultrasound-microwave method were 3.79 g/g, 1.39 mL/g, and 1.14 g/g, respectively, a 9.54%, 23.01%, and 17.53% increase from the values of raw SDF. The WHC, WSC, and OHC of SDFs modified via the enzyme method were 3.59 g/g, 1.25 mL/g, and 1.03 g/g, respectively, with a 3.76%, 10.62%, and 6.19% increase when compared to raw SDFs. The cholesterol-binding capacity of SDFs modified via the ultrasound-microwave and enzyme methods was 13.82 and 12.34 mg/g, respectively, with an increase of 47.98% and 32.20% when compared to raw SDFs. The changes in structure and physical and chemical properties were shown to be closely related to the significantly improved cholesterol-binding capacity of the SDFs from modified black soybean hulls. This provides a theoretical basis for subsequent research and development of black soybean hulls products. PRACTICAL APPLICATION: At present, the black soybean hull, a byproduct of general grains, is usually abandoned, but black soybean hull is rich in dietary fiber. Enzymatic modification and ultrasound-microwave comodification were used to treat black soybean hull to prepare small molecular weight, highly active soluble dietary fiber. This research is of great significance to the deep processing of black soybean hull and improvement of the economic benefits of black soybean byproducts.