Purification, structural characterization, and in vitro fermentation properties of okra polysaccharides

Abstract

In this study, two components of okra polysaccharide (OP-12 and OP-14) were isolated and purified. Their chemical structures and in vitro fermentation characteristics were studied to explore the structure-activity relationship in improving intestinal microecology. Results showed that OP-12 and OP-14 had structural differences. Compared with OP-14, OP-12 had higher neutral sugar content, molecular weight (Mw), and degree of branching. The most abundant monosaccharides in OP-12 were rhamnose (Rha) and galactose (Gal), while those in OP-14 were galacturonic acid (GalA). Methylation and nuclear magnetic resonance (NMR) analysis suggested OP-12 and OP-14 were likely pectin polysaccharides containing rhamnogalacturonan I (RG-I) domain and homogalacturonans (HG) domain, respectively. Furthermore, OP-12 and OP-14 with different chemical structures had differences in bacterial density, sugar consumption rate, short-chain fatty acids (SCFAs) production and intestinal microbiota composition during the fermentation process. OP-14 was rapidly utilized by intestinal flora at the early stage, whereas OP-12 was preferentially consumed in the middle-late stages. Correlation analysis revealed that the monosaccharide composition, degree of branching, and Mw of okra polysaccharides were closely related to the regulation effect of the gut microbiota and the types and concentrations of SCFAs.