Comparison in the Structure and Physicochemical Properties of Soybean Dregs Insoluble Dietary Fiber from Different Sources

This study aimed to prepare soybean dregs insoluble dietary fiber generated from the processing of traditional soybean products (TBP-IDF) and to compare the differences in structure and physicochemical properties between it and insoluble dietary fiber prepared from soybean protein isolate processing by-products (SPI-IDF). The optimal degreasing process of soybean dregs was optimized by single-factor experiments and response surface methodology. TBP-IDF was prepared by a complex enzymatic method and its basic components and fractions were determined. The structural differences between TBP-IDF and SPI-IDF were compared using ion chromatography, scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. Differences in the physicochemical properties of TBP-IDF and SPI-IDF were analyzed by determining water-holding capacity, swelling capacity, oil-holding capacity, glucose-absorption capacity, and cholesterol-adsorption capacity. The results showed that the optimal defatting process parameters for traditional soybean dregs were as follows: liquid-to-feed ratio of 22:1, treatment temperature of 59 ℃, and treatment time of 70 min, under which the defatting rate of soybean dregs reached 90.13%. The content of TBP-IDF was up to 83.23%, with 29.3% cellulose, 53.5% hemicellulose, and 17.2% lignin. Compared with SPI-IDF, there were significant differences in the composition of the monosaccharides of TBP-IDF, with significantly increased glucose content (P<0.05), but the advanced structure was similar. The water-holding capacity (9.53 g/g) and swelling capacity (5.20 mL/g) of TBP-IDF were significantly higher than SPI-IDF (7.73 g/g, 4.30 mL/g) (P<0.05), while the oil-holding capacity (6.22 g/g) was significantly lower than SPI-IDF (7.95 g/g) (P<0.05). The adsorption capacity of both for glucose and cholesterol increased with the increase of substrate concentration, and there was no significant difference (P>0.05). This study demonstrated that TBP-IDF had similar potential physiological activities with SPI-IDF, which could potentially be used as a functional food ingredient for assisting glycolipid metabolism, and expanded the sources and ways of preparing soybean insoluble dietary fiber.