Optimization of Selenized Bletilla striata Polysaccharides Preparation by Response Surface Methodology and Determination of the Antioxidant Activity in Vitro

In this study, the preparation process of selenized Bletilla striata polysaccharides (BSP-Se) was optimized, to explore whether higher antioxidant activity preparation could be obtained. BSP-Se was prepared by using Bletilla striata polysaccharide (BSP) as the raw material, Na₂SeO₃ as the selenifying agent, and acetic acid as the catalyst. Taking selenium content as an indicator, the preparation process was optimized using single factor experiments and response surface methodology. Fourier-transform infrared spectroscopy was used to determine whether BSP-Se was successfully prepared, and the antioxidant activity of BSP-Se in vitro was evaluated by measuring the scavenging ability of DPPH, ABTS⁺ and ·OH free radicals. The results showed that the selenium content of BSP-Se prepared under the optimal process conditions of Na₂SeO₃ to BSP mass ratio of 1.5, acetic acid to BSP dosage ratio of 3, reaction time of 6 hours, and reaction temperature of 80 ℃ was the highest, reaching 7.831 mg/g. FT-IR analysis showed that selenium binds to BSP through Se-O-C and O-Se-O, indicating that the polysaccharides have been successfully selenified. The analysis of free radical scavenging ability showed that the IC₅₀ values of BSP-Se for DPPH, ABTS⁺, and ·OH free radicals were 2.875, 4.431 and 0.314 mg/mL, respectively, which were significantly lower than the IC₅₀ values of 5.828, 8.475 and 0.833 mg/mL of BSP (P<0.05), indicating that selenization modification improved the antioxidant capacity of BSP. Therefore, the antioxidant activity of BSP can be improved by selenization modification, which provides a theoretical basis for further research on the application of selenium polysaccharides as a new antioxidant in the fields of foods and medicine, health care products and daily chemical.