Characterization and immunomodulatory activity of rice hull polysaccharides

Rice hulls (Oryza sativa) are high in carbohydrate content and have been utilized as dietary fiber. The immunomodulatory bioactivity of rice hull polysaccharides (RHPS) has rarely been reported. This study demonstrated the structural characteristics and immunomodulating of RHPS. The RHPS were fractioned using DEAE-650M column, producing one neutral and 3 acidic polysaccharide fractions. RHPS were examined using HPAEC-PAD, HP-SEC, NMR and GC-MS for structural characteristics. The results showed that RHPS consisted of arabinose, galactose, glucose, mannose, and xylose in ratios of 10:44.8:29.8:9.3:6.1 and comprised (1→3)-Gal as backbone, and its average molecular weight was 77kDa. The presence of type II arabinogalactan (AGII) was confirmed through LM2-ELISA and Yariv gel diffusion showed the RHPS had AGII features. This study examined the immunomodulatory effects of orally administering RHPS in vivo. The RHPS increased the cytotoxicity of splenic natural killer cells, macrophage phagocytosis, and cytokine inductions. This is the first study to demonstrate the structural characteristics of an active polysaccharide from rice hulls and its immunopharmacological effects in vivo.