Modeling of anthocyanins adsorption onto chitosan films: An approach using the pore volume and surface diffusion model

The use of smart packaging is a global trend, and several works are being reported in this sense. Special attention is given to biodegradable materials like chitosan and natural pigments like anthocyanins. For example, previous studies report that it is possible to produce smart packaging by extracting anthocyanins from red cabbage and adsorbing it into chitosan films. This work elucidates for the first time the mass transfer aspects in the anthocyanins adsorption on chitosan films (CFS). Anthocyanins were extracted from red cabbage and subsequently adsorbed from the leach liquor using chitosan films. The Freundlich model well represented the adsorption isotherms of anthocyanins on CFS. In addition, the PVSDM (pore volume and surface diffusion model) model was implemented to represent the adsorption data and to elucidate the mass transfer. This model was suitable to represent the adsorption data, with a coefficient of determination (R2) higher than 0.95 and an average relative error (ARE) lower than 2.00%. The surface diffusion coefficient values (DS) ranged from 3.70 × 10−10 cm2 s−1 to 1.16 × 10−9 cm2 s−1. The external mass transfer coefficient (kF) was in the range of 10−2 cm s−1. Finally, the Biot number (Bi) revealed that mechanisms inside the particle controlled the anthocyanin's adsorption onto CFS.