Chinese yam (Dioscorea polystachya Turcz.) peel is richer in nutritional components and exhibits distinct polysaccharide/oligosaccharide structures compared with the flesh

Chinese yam ( Dioscorea polystachya Turcz.) is widely cultivated in China for both food and medicinal purposes, yet large amounts of peel are discarded during processing. To assess its potential utilization value, we compared the nutritional composition and functional carbohydrate (polysaccharide and oligosaccharide) structures of the peel and flesh from four representative Chinese yam varieties (Tiegun, Changyu, Jiujinhuang, and Xiaobaizui). Results showed that the peel contained significantly higher levels of protein, ash, dietary fiber, flavonoids, and phenols than the flesh, although carbohydrates were predominant in both. Structural analyses showed that peel polysaccharides were mainly mannose-based, exhibiting compact and thermally stable structures, whereas flesh polysaccharides were glucose-dominant with higher molecular weights. Peel oligosaccharides were rich in fructo-oligosaccharides, suggesting prebiotic potential, while flesh oligosaccharides consisted primarily of maltose-like glucans. These results highlight the nutritional and functional value of yam peel, supporting its high-value recovery and application in food and health industries. • The nutritional content of yam peel was significantly higher than yam flesh. • The structure of polysaccharide varied between yam peel and flesh. • Oligosaccharides in yam peel were dominated by fructo-oligosaccharides. • The by-products of yam processing possess potential for high-value utilization.