Ultrasound-assisted extraction of insoluble dietary fiber from soybean and its physical properties

The effects of ultrasound-assisted extraction on extraction rate and physical characteristics of water insoluble dietary fibers (IDF) were studied. Based on the single factor experiments : the ratio of water to dry soybean dregs powder, ultrasonic power intensity, ultrasonic temperature and extraction time, the four-factor second order rotation combination experimental design was applied to optimize the parameters for IDF of ultrasound-assisted extraction. The physical characteristics of the IDF obtained by technology of ultrasound-assisted extraction (UAE) were examined by a combination of chemical and instrumental analysis approaches, including water-holding, extension, water-binding, fat-binding capacities, SEM, Fourier transform infrared (FT-IR) spectra and TG, and compared with acid dissolution and alkali precipitatiom (ADAP) and enzyme-assisted extraction (EAE). The results indicated that the highest yield of 92.11% was reached under the conditions which the ratio of water to dry soybean dregs power was 35 mL/g, ultrasonic power intensity 600 W/g, ultrasonic temperature 50 ℃ and extraction time 50 min. The IDF obtained by UAE had higher water-holding, extension, water-binding and fat-binding capacities, and much abundant reticular structure than those obtained by ADAP and EAE. The analytic data of FT-IR and TG indicated that ultrasound treatment could raise the free hydroxyl groups, but did not change its pyrolysis mechanism. In conclusion, UAE not only increased the extraction rate of IDF, but also improved physical characteristics.