Effects of the steaming process on the structural properties and immunological activities of polysaccharides from Polygonatum cyrtonema

Steaming significantly decreased the polysaccharide content in the rhizome of Polygonatum cyrtonema. This study aimed to reveal the effects of steaming on structural characteristics and immunomodulatory activities of Polygonatum cyrtonema polysaccharide (PCP). The results showed that steaming decreased the polysaccharide content in the rhizome by 38.41%. Structural changes of PCP by steaming included molecular degradation, aggregation, and depolymerization, which also affected its immunological activities. Steaming first degraded β-type fructofuranose in PCP from raw rhizome. However, steaming for 2 h and 4 h increased the molecular weight and particle size, and changed the monosaccharide composition of the PCPs. Additionally, PCP at 2 h and 4 h had higher immunological activities than PCP from raw rhizome. Then, a longer steaming time (6–12 h) caused excessive destruction of PCP and had negative impacts on their immunological activities. These results revealed changes in PCP during the steaming process and provided a reference for the processing of Polygonatum cyrtonema, especially for avoiding overprocessing.