Abstract: Response surface methodology was applied to optimize the ultrasonic-assisted extraction of crude polysaccharide from Nostoc commune vauch based on the results of single factor including the effect of solid-liquid ratio,ultrasonic temperature,ultrasonic power and ultrasonic time on the yield of crude polysaccharides.A kinetic model of crude polysaccharide extraction was established according to Fick's second law,and the dynamics parameters such as rate constant,relative extraction rate and activation energy were obtained.Meanwhile,thermodynamic properties were studied.The results showed that optimal extraction condition of crude polysaccharide was solid-liquid ratio of 1/50 (g/mL),ultrasonic temperature of 350.15 K,ultrasonic power of 540 W and ultrasonic time of 25 min,the yield of crude polysaccharide was up to 13.07% under above condition.The extraction process conforms to the first-order kinetic model,and the experimental data agreed well with the calculated values of the kinetic model.Thermodynamic analysis showed that the extraction process of polysaccharides from N.commune was endothermic,irreversible and spontaneous.

Key words: Nostoc commune vauch, ultrasonic assisted polysaccharides extraction, response surface analysis, kinetics and thermodynamics