The effects of different extraction methods on the structure and antioxidant properties of Bletilla striata polysaccharide

Bletilla striata polysaccharide (BSP) is one of the main active ingredients of the traditional Chinese medicine Bletilla striata (Thunb) Richb.f and the extraction method of BSP has a significant impact on its properties. This study investigated the effects of four extraction methods, namely hot water extraction, ultrasonic extraction, enzyme extraction, and microwave extraction, on the structure and antioxidant properties of BSP. Characterization results from FTIR and NMR showed that all four BSP consisted mainly of glucose and mannose, forming α-glycosidic and β-glycosidic linkages to form glucomannan. Hot water extraction had the lowest extraction rate of BSP at 21.78% ± 0.73%. The polysaccharide BSP-H obtained from hot water extraction had the smallest absolute Zeta potential and Grain size, but the largest molecular weight at 204 kDa. It exhibited the best thermal stability and superior antioxidant activity compared to polysaccharides extracted using the other three methods, as evaluated by three different antioxidant assays. Although the antioxidant activity of BSP-V was slightly weaker, it showed a significant improvement compared to the remaining two polysaccharides. These results suggest that hot water extraction is the most suitable method for large-scale application of BSP, preserving its activity effectively, thus facilitating practical production and product development.