Optimization and kinetic/thermodynamics analysis of ionic liquid based ultrasonic-assisted extraction of proanthocyanidins from pomegranate seeds

The ionic liquid based ultrasonic-assisted extraction conditions of proanthocyanidins from pomegranate seeds were studied.Single factor test and Box-Behnken experimental design were used to optimize the extraction process employing proanthocyanidins yield as the response, and extraction time, extraction temperature, ultrasonic power and concentration of ionic liquid were used as independent variables. The kinetics and thermodynamics of extraction process was studied basing the optimized extraction conditions.Results showed that the optimal extraction conditions for proanthocyanidins were determined as follows: extraction time of 32 min, extraction temperature of 52 ℃, ultrasonic power of 300 W, and concentration of ionic liquid of 1.15 mol/L.Under these conditions, the yield of proanthocyanidins was 1.718%. Kinetic parameters showed that extraction rate constant k value was 0.313 min-1, surface diffusion coefficient DSvalue was 7.936 × 10-5cm2/min while those of ethanol control group were 0.063 min-1and 1.597 × 10-5cm2/min, respectively, and the extraction rate was significantly improved.Thermodynamics parameters showed that entropy ΔH was 248.51 k J/mol, enthalpy ΔS was 813.69 J/ ( mol·K) , the values were all greater than zero, indicating that the ionic liquid extraction process was an endothermic process of increasing entropy, at the same time, the free energy ΔG was-18.254 k J/mol, less than zero, indicating that the ionic liquid extraction process was a spontaneous process.Both the optimized ionic liquid extraction technique and dynamics/thermodynamics analysis can be used for industrial scale-up and optimal control of proanthocyanidins extraction from pomegranate seeds.