Oxidation kinetics and thermodynamic analysis of chia oil microencapsulated in a whey protein concentrate-polysaccharide matrix

The oxidation kinetics of chia oil (CO) in bulk and microencapsulated by spray-drying in a biopolymer matrix of whey protein concentrate (WPC) with mesquite gum (MG) (67:33 w/w ratio) stored at 25, 35 and 40 °C at different water activities (aw) were determined. Oxidation was described by a zero-order kinetic equation of the autocatalytic type in all cases. The oxidation of CO within microcapsules was slower than in bulk, independently of the storage temperature. The kinetics parameters, rate constant and activation energy, decreased as aw increased. In the aw range between 0.614 and 0.654 both kinetic parameters presented the lowest values, which corresponded to the minimum integral entropy (ΔSint)T zone. The (ΔSint)T zone is considered as the zone of maximum stability as less water is available to participate in degradation reactions, acting as plasticizer in the polymeric matrix and hindering oxygen diffusion through the pores, retarding the oxidation process.