A Polysaccharide from Dried Tangerine Peel: Structural Characterization and Alleviation of Gastric Injury by Modulating Oxidative Stress and Inflammatory Responses

Polysaccharides are important bioactive components of dried tangerine peel, exhibiting antioxidant, anti-inflammatory, and hypoglycemic activities. However, the ability of dried tangerine peel polysaccharides to alleviate gastric injury remains insufficiently understood. Therefore, the structure and alleviation of gastric injury induced by dried tangerine peel polysaccharides were explored in this study. Firstly, DTPP-4 was purified from dried tangerine peel. As shown in the HPLC chromatogram, DTPP-4 is a homogeneous polysaccharide with a mean molecular weight of 1.35 × 103 kDa. DTPP-4 was mainly composed of L-Rha, L-Ara, D-Gal, and D-GalpA with percentages of 10.56%, 9.15%, 4.83%, and 75.45%, respectively. Methylation and NMR results suggested that DTPP-4 was a pectic polysaccharide with →4)-α-D-GalpA-6-OMe-(1→ and →4)-α-D-GalpA-(1→ as the backbone. The alleviation of gastric injury of dried tangerine peel polysaccharide was evaluated in ethanol-induced acute gastric injury mice. Based on the macroscopic images of gastric tissues and the area of gastric tissue injury in mice, the dried tangerine peel polysaccharide can reduce the mouse gastric lesion area and alleviate gastric tissue pathological damage. Histopathological analysis of H&E and PAS staining revealed that the dried tangerine peel polysaccharide could ameliorate the disordered arrangement and necrosis of epithelial cells, reduce inflammatory cell infiltration, and thus alleviate gastric injury. Dried tangerine peel polysaccharide confers gastroprotection by modulating MPO and PGE2 levels, reducing MDA accumulation, enhancing SOD and CAT antioxidant activities, suppressing IL-1β and TNF-α secretion, and upregulating IL-10 expression. These findings provide a theoretical foundation for subsequent structure–activity relationship investigations and provide empirical support for the subsequent development and practical application of this polysaccharide.