Kinetics and thermodynamics of water extraction of foxtail millet polysaccharides

Abstract

In order to understand the mechanism of the extraction process of polysaccharides from foxtail millet by hot water, the extraction was carried out for studying the kinetics and thermodynamics of extraction process. After the appropriate stirring rate and liquid material ratio was selected through preliminary experiment, the changes of polysaccharides mass concentration in the extract liquor with extraction temperature and extraction time were measured. The experimental data were fitted by the first-order model. The kinetics and thermodynamics parameters were calculated. The results showed that the appropriate stirring rate and liquid material ratio was 150 r/min, 20.0 mL/g respectively. The greater extraction rate and higher equilibrium mass concentration could be obtained under higher extraction temperature. The extraction process accorded with the first-order dynamics model. The apparent activation energy of process was 12.03 kJ/mol under study conditions. The internal diffusion coefficient was increased with increasing temperature in the range of 7.84×10-10 - 1.29×10-9 m2/min. The half-life was decreased from 25.2 min to 3.9 min as temperature increased. The Gibbs free energies were all less than zero, the enthalpy change was 31.96 kJ/mol and the entropy change was 120.3 J/(mol·K) in process. The polysaccharides extraction process was a spontaneous, endothermic and entropy increases process.