Extraction, Purification, Structural Characterization, and In Vitro Simulated Digestion of Polysaccharides from Elaeagnus angustifolia

To exploit medicinal and edible plant resources, this study investigated the extraction, structural characterization, and in vitro digestion of Elaeagnus angustifolia polysaccharide (EAP). Despite the nutritional value of this polysaccharide, its digestive properties remain unclear. Ultrasound-assisted extraction was optimized via response surface methodology. Crude EAP was purified by AB-8 macroporous resin purification and decolorization, followed by deproteinization and dialysis. The purified product (91.07% total sugar; 2.37% protein) was characterized by ultraviolet (UV) spectroscopy, Fourier-transform infrared (FT-IR) spectroscopy, high-performance liquid chromatography (HPLC), and gel permeation chromatography (GPC), and its digestion profile was assessed using a three-stage in vitro model (INFOGEST 2.0). Under optimal conditions, the crude polysaccharide yield (based on ethanol-precipitated solid; 87.83% total sugar) reached 2.44 ± 0.01%. EAP was identified as a pyranose-type polysaccharide, with glucose, mannose, and galactose as the predominant monosaccharides (relative molar proportions, 0.470:0.199:0.081, normalized to the total detected monosaccharides), with a weight-average molecular weight of 1.739 × 105 g·mol−1. In vitro digestion revealed negligible digestibility in the oral phase (0%), and low digestibility in the gastric (0.55%) and intestinal (2.76%) phases, with a cumulative digestibility of 3.30%. This marked resistance to gastrointestinal digestion indicates EAP is a partially digestible polysaccharide with potential prebiotic properties. The demonstrated resistance to gastrointestinal breakdown provides a theoretical basis for the high-value utilization of EAP in functional foods as a potential fermentable substrate for gut microbiota modulation.