Mass transfer mechanism of the multivariate consecutive extraction process of pectin and hesperidin from Citrus aurantium L.: Kinetics, thermodynamics, diffusion and mass transfer coefficients

In the previous research, the multivariate consecutive extraction process of pectin and hesperidin from FAI was completed, and it was found that the extraction efficiency of hesperidin could be significantly improved because of the priority extraction of pectin. The main objective of this paper is to further elucidate the mass transfer mechanism of the extraction process. The kinetics, thermodynamics, activation energy, diffusion coefficients, mass transfer coefficients and Biot number of the multivariate consecutive extraction process as well as the single extraction process of hesperidin in FAI were estimated and compared. It was confirmed that the mass transfer of the process was effectively strengthened because of the priority extraction of pectin from FAI. Its kinetic data was demonstrated to the pseudo-second-order kinetic model, and the activation energy of hesperidin extraction was as low as 2.27 kJ/mol, far lower than that of the single extraction process (16.67 kJ/mol). In particular, the diffusion coefficien and mass transfer coefficient were larger while the Biot number was lower compared with the single extraction process. These results further proved that the priority extraction of pectin from FAI led to the destruction of cell structure and the exposure of hesperidin crystals, which can effectively reduce the internal resistance of the mass transfer and the activation energy of extraction process, therefore accelerating the penetration and wetting of the extractant into the raw material internally, improving the transfer of hesperidin from the inside to the surface of the raw material as well. In addition, the extraction thermodynamics illustrated that the extraction process of hesperidin was endothermic, irreversible and spontaneous.