Effects of different drying methods on the physicochemical and antioxidative characteristics of Osmunda japonica Thunb. polysaccharides

To select a suitable drying pretreatment method to obtain biologically active polysaccharides with a required function, fresh Osmunda japonica Thunb. was subjected to natural drying (ND), hot air drying (HD), and vacuum freeze-drying (FD) treatments. After pretreatment, the O. japonica Thunb. polysaccharides (OPs) were extracted and denoted ND-OP, HD-OP, and FD-OP. The chemical composition, physicochemical characteristics, and antioxidant activities of the OPs were analyzed. The drying method substantially influenced the OPs. HD-OP had the highest yield (4.88%) and uronic acid content (9.17%) and the lowest molecular weight (252.54 kDa). Moreover, based on the correlation analysis, the high uronic acid content, low molecular weight, and unique monosaccharide composition may be closely related to the stronger antioxidant activity of HD-OP. The above results indicate that HD is the best method for the industrial production of high-quality OPs. Practical applications The picking period of O. japonica Thunb. is short and it should be processed in time after harvesting. By choosing a suitable drying pretreatment method, we can obtain bioactive polysaccharides with desired functions, and we hope to have good application prospects in medicine, cosmetics, food, and other fields. This can also transform OPs into products with added economic value.