Chemical Compositions and Prebiotic Activity of Soy Hull Polysaccharides <i>in Vitro</i>

Soy hull polysaccharides (SHPs) were extracted from soy hull using microwave-assisted extraction and their structures were investigated by Fourier transform infrared spectroscopy (FT-IR) and atomic force microscopy (AFM). Subsequently, the effects of SHPs on the proliferation of fecal microbiota were examined. The results indicated that microwave-assisted extraction had significantly higher efficiency in extracting SHPs. The yield of microwave-assisted oxalic acid extracted soy hull polysaccharide (MOS) and microwave-assisted ammonium oxalate extracted soy hull polysaccharide (MAS) increased by 33.4% and 17.4%, when compared with oxalic acid extracted soy hull polysaccharide (OS) and ammonium oxalate extracted soy hull polysaccharide (AS), respectively. High performance liquid chromatography showed that the four polysaccharides had significant differences in their monosaccharides composition. High performance gel filtration chromatography illustrated that the molecular weights of MAS and AS were the highest. FT-IR spectra indicated that the structures of MOS and OS were similar and mainly comprised furanose, whereas MAS and AS mostly consisted of pyranose. AFM showed that the molecular chain conformation of MOS and MAS was vermicular, OS was short-rod-like, and AS was rod-like. MOS significantly promoted proliferation and diversity of fecal bacteria. Interestingly, OS enhanced the growth of Bifidobacterium spp. and Lactobacillus spp. In summary, SHPs showed more potent prebiotic activity with microwave-assisted extraction method and could have prospective applications in functional food industry.