Effects of aging on the fine structure, chain conformation, and morphology of Chenpi polysaccharides

The aging process endows Chenpi (Pericarpium Citri Reticulatae) with unique value and efficacy. This study investigated the dynamic changes in the fine structure, chain conformation, and morphology of water-soluble polysaccharides from Chenpi over time. In the initial storage period of Chenpi (1 year), Chenpi polysaccharides (CP) exhibited a triple-helical structure, with chains entangled and aggregated into rough spherical conformations. Galacturonic acid (GalA, 47.78 mol%) was the predominant monosaccharide. As aging progressed, the homogalacturonan (HG) regions gradually degraded, leading to decreases in molecular sizes (particle size, M_w, M_n, and R_g), a reduction in the degree of esterification, and a weakening of the semicrystalline structure. Consequently, arabinose (Ara) emerged as the main monosaccharide (41.38 mol%). Neutral sugars continuously enriched the rhamnogalacturonan (RG-I) side chains, forming highly branched single molecules that curled into spherical shapes. By 15 years, CP were fully degraded, adopting a compact molecular conformation with the triple-helix structure disappearing and sizes uniformly below 20 nm. However, AFM results indicated aggregation phenomena in 15-year CP. Additionally, CP viscosity decreased while thermal stability improved, reflecting the natural structural transformation of CP. This study provides scientific evidence supporting the application of Chenpi in the food and pharmaceutical industries.