Structure of Soluble Dietary Fiber from Fresh Rice at the Medium-Milk Stage and Improvement of Insulin Resistance in HepG2 Cells

Abstract

Fresh rice (Oryza sativa ssp. japonica) at the medium-milk stage is rich in soluble dietary fiber (SDF), leading to potential effects on type 2 diabetes (T2D). In this study, we analyzed each monosaccharide, the relative molecular weight, and the molecular linkages of fresh rice (grain, stem, husk, and leaf) SDF. The examined fresh rice leaf SDF consisted of 31.9% glucose, 35.7% galactose, 15.3% arabinose, 11.7% mannose, and a small amount of rhamnose and xylose. The molecular weight ( $M_{\text{w}}$ ) was $232.5\pm 19.1\times {10}^4\text{u}$ , and the radius of gyration ( $R_{\text{g}}$ ) was $298.8\pm 25.4\text{nm}$ . The glycosidic bonds consisted mainly of Araf and Glc/Gal and included 1,3-Araf, 1,5-Araf, and 3,5-Araf glycosidic bonds. The effect of fresh rice leaf SDF on insulin resistance (IR) in HepG2 cells showed that it could significantly enhance glucose consumption ( $P<0.05$ ). It also decreased the malondialdehyde (MDA) content ( $P<0.05$ ) and increased the total superoxide dismutase (T-SOD) and glutathione peroxidase (GSH-Px) activities ( $P<0.05$ ) in a dose-dependent manner. Therefore, fresh rice leaf SDF might be a good dietary supplement for treating T2D.