Structural characteristics and functional properties of soluble dietary fiber from defatted rice bran obtained through Trichoderma viride fermentation

Trichoderma viride was utilized to ferment the defatted rice bran (DRB), and soluble dietary fiber was prepared before and after fermentation, named as B-SDF and F-SDF, respectively. Optimum fermentation conditions for yield of F-SDF were determined using response surface methodology (RSM). The yield of F-SDF was significantly increased from 10.5 (w/w, %) to 33.4 (w/w, %) under the optimal conditions (inoculum size = 10%, pH = 5.8 and time = 41 h). Fourier transform infrared spectroscopy (FTIR) demonstrated that both B-SDF and F-SDF had typical characteristics of the infrared spectrum of polysaccharides, and X-ray diffraction (XRD) revealed they were mainly substances of amorphous structure. In addition, F-SDF showed looser structure by scanning electron microscopy (SEM) analysis, increased molecular weight by high-performance gel permeation chromatography (HPGPC) analysis, and more complex monosaccharide composition by high-performance anion exchange chromatography (HPAEC) analysis. Furthermore, functional properties analysis showed that F-SDF exhibited higher water-holding capacity (WHC), oil-holding capacity (OHC), water solubility (WS) and cholesterol absorption capacity (CAC) than B-SDF. In summary, the present study suggested that SDF from defatted rice bran obtained through Trichoderma viride fermentation has a higher potential to be used as a functional ingredient in foods.