Optimization of Alkali Extraction Process of ‘Jinsixiaozao’ Polysaccharide by Response Surface Methodology and Its Antioxidant Activity

In this experiment, ‘Jinsixiaozao’ fruit was used as raw material, the effects of extraction temperature, time, solid-liquid ratio and NaOH concentration on the yield of polysaccharide were investigated by single factor test. On this basis, Box-Behnken experiment was carried out to optimize the extraction process of alkali extracted polysaccharides. Its total sugar content, scanning electron microscopy, infrared spectrum and antioxidant activity were determined. The results showed that the optimal conditions were solid-liquid ratio 1:35 (g/mL), extraction temperature 80 ℃, extraction time 120 min, and NaOH concentration 0.2 mol/L, the polysaccharides yield was 11.44% with total sugar content of 69.39%. Scanning electron microscopic observations showed that it had irregular block structure with compact inside. The infrared spectrum showed that the alkali extracted polysaccharide of jujube had the characteristic absorption peaks of acid polysaccharides such as C=O and C-H. The antioxidant activity experiments showed that the alkali extracted polysaccharide had a certain ability to scavenge free radicals, and the IC₅₀ for DPPH and superoxide anion free radicals were 1.201 mg/mL and 1.176 mg/mL, respectively. This study provides a reference for further developing functional foods of jujube polysaccharides and studying the structure-activity relationship of alkali extracted polysaccharides.