Study on the kinetic model, thermodynamic and physicochemical properties of Glycyrrhiza polysaccharide by ultrasonic assisted extraction.

The extraction process of crude polysaccharides from Glycyrrhiza (GP) by ultrasonic assisted hot water method was established according to the optimized kinetic model based on Fick's second law of diffusion, and thermodynamic action was analyzed. Physicochemical properties of GP including the apparent viscosity, thermostability and antioxidant activities etc. were determined by ultraviolet spectrophotometry and differential scanning calorimetry (DSC). Characteristic function groups and surface structure also were analyzed by Fourier infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and atomic force microscopy (AFM), respectively. The results showed the extraction kinetic curves of GP showed good linear correlation with the linear correlation coefficients (R2) of equal or greater than 0.90 based on Fick's second law of diffusion, and the maximum yield of 3.53% was obtained at 343.15 K and ultrasonic power 600 W with material-liquid ratio of 1:15 for 60 min. Gibbs free energy change (ΔGm > 0) indicated that the extraction process was endergonic and not spontaneous. GP was confirmed a kind of acidic pyran polysaccharide with small bubble-like holes internally. The GP viscosity increased with the increase of concentration and then gradually decreased with the enhancement of shear rate. GP showed good thermal stability along with two stages of mass loss by DSC analysis. The antioxidant activity experiments suggested that the higher the concentration of GP, the stronger its reduction power.