Ultrasound-assisted alkali extraction of insoluble dietary fiber from soybean residues

Dietary fiber is a carbohydrate-based polymer with significant health benefit, soybean residues are generally discarded in food industries during the production of soybean milk and tofu. In this study, ultrasound-assisted alkali extraction technology was employed to extract insoluble dietary fiber from soybean residues. And the physicochemical properties of insoluble dietary fibers were also studied. The optimal conditions for insoluble dietary fibers were determined to be solid to liquid ratio of 1:50, alkali concentration of 0.05 mol/L, ultrasound power of 450 W, reaction time of 10 min and reaction temperature of 30 °C. The yield of insoluble dietary fiber was 744.3 ± 13.2 mg/g raw soybean residues using the combination of ultrasound and alkali. In addition, the insoluble dietary fibers had higher water retention capacity, swelling capacity than those of untreated soybean residues, while the oil retention capacity of insoluble dietary fibers was lower than that of untreated soybean residues.