Structure and In Vitro Fermentation Characteristics of Polysaccharides Sequentially Extracted from Goji Berry (<i>Lycium barbarum</i>) Leaves

Abstract

Herein, the chelating agent-soluble fraction (CA), sodium carbonate-soluble fraction (SC), and sodium hydroxide-soluble fraction (SH) were sequentially extracted from the cell wall of goji berry (<i>Lycium barbarum</i>) leaves. Furthermore, SC was purified with Q-Sepharose fast flow resin to obtain the neutral sugar fraction (SC-I) and acid sugar fraction (SC-II). Physicochemical properties of polysaccharides were characterized by high-performance anion-exchange chromatography with pulsed amperometry detection, size exclusion chromatography-multi-angle laser light scattering, Fourier transform infrared spectroscopy, nuclear magnetic resonance, and atomic force microscopy analysis. Additionally, the impact of polysaccharides on modulating human gut microbiota was investigated by <i>in vitro</i> fermentation. A high amount of galacturonic acid (GalA) in CA showed that it was an aggregation of linear homogalacturonan. SC was the main pectic polysaccharide fraction and rich in neutral sugars. SC-I was the neutral sugar fraction with an extremely high molecular weight (2.055 × 10⁶ Da), while SC-II was the acid sugar fraction with a low molecular weight (1.766 × 10⁵ Da). SH seemed like a mixture of pectin and hemicellulose. All the five polysaccharides significantly (<i>P</i> < 0.05) increased the abundance of <i>Bacteroides</i>, <i>Bifidobacteria,</i> and <i>Lactobacilli</i>. To the best of our knowledge, this is the first report on the structure and fermentation characteristics of goji berry leaf polysaccharides, which is meaningful to provide a structural basis for further bioactivity research.