Enzymatic Modification of Rice Bran Polysaccharides by Enzymes from Grifola Frondosa: Natural Killer Cell Cytotoxicity and Antioxidant Activity

• Autores: Shiyao Liu, Xuhui Zhang, Xiaolin Zhang, Wei Han, Yuchun Liu, Dongmei Sun, Weiqun Guo
• Localización: Journal of food science, ISSN 0022-1147, Vol. 83, Nº 7, 2018, págs. 1948-1955
• Idioma: inglés
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• Resumen

  • Rice bran polysaccharides (RBPSs) are the major active constituents of rice bran (RB). In this study, we utilized intracellular enzymes from Grifola frondosato modify RBPSs, which were extracted from RB using ultrasound. To enhance the effect on natural killer (NK) cell cytotoxicity of modified polysaccharides (mRBPSs) generated from RBPSs, an orthogonal test (L9[3]4) was employed to optimize the modification conditions. Based on the results of a single‐factor test, the enzyme to polysaccharide ratio, reaction temperature, reaction pH, and reaction time were the main factors affecting mRBPSs‐enhanced NK‐cell cytotoxicity. The best conditions were determined to be an enzyme to polysaccharide ratio of 1:5, a reaction temperature of 40 °C, a reaction pH of 4, and a reaction time of 4 hr. By optimizing the conditions, the NK‐cell cytotoxicity induced by mRBPSs6was the highest, increasing by 12.01% ± 0.08%. Gas chromatographic analysis revealed that mRBPSs6consists of rhamnose, arabinose, xylose, mannose, glucose, and galactose at a molar ratio of 7:21:6:5:53:48, which was 8:13:8:5:44:44 before modification. High‐performance liquid chromatography results indicated molecular weights for the RBPSs of approximately 106Da, which decreased to 104to 105Da after modification. Antioxidant activity tests revealed high capacity of mRBPSs6for scavenging 1,1‐diphenyl‐2‐picrylhydrazyl radicals and hydroxyl free radicals at 1.0 mg/mL. Rice bran polysaccharides (RBPSs) contain compounds with many biological activities. However, these polysaccharides difficult to absorb due to high molecular weights and unexposed active sites, which are the main factors that limit their use in functional foods. The results of this study demonstrate that modification of RBPSs using intracellular enzymes from an edible fungus alters the molecular weights and monosaccharide composition of RBPSs. In addition, immune and antioxidant activities of RBPSs were increased. The findings provide a new and beneficial application for rice bran.