Predicting suitable storage conditions for spray-dried microcapsules formed with different biopolymer matrices

Canola oil (CO)-in-soy protein isolate (SPI, 12.5 g per 100 ml of solution), CO-in-whey protein concentrate (WPC, 30 g per 100 ml of solution) and CO-in-mesquite gum (MG, 30 g per 100 ml of solution) emulsions were obtained (all with CO to biopolymers solids ratio of 25 g of canola oil per 100 g of wall material), spray dried and stored at water activities (aw) of 0.12–0.89 at temperatures of 15, 25 and 35 °C. The powders adsorption isotherms experimental data were fitted to the GAB model. Their differential and integral enthalpies and entropies were estimated. The microcapsules point of minimum integral entropy (maximum stability) kept at 25 °C occurred at 10.40 g water per 100 g of dry solids (aw of 0.55) for MG, 10.59 g water per 100 g of dry solids (aw of 0.68) for SPI, and 6.38 g water per 100 g of dry solids (aw of 0.46) for WPC. The integral enthalpy–entropy compensation indicated that the water vapour adsorption was controlled by entropic mechanisms at low aw, but by enthalpic mechanisms at high aw.