Effects of Storage Temperature and Water Activity on the Degradation of Carotenoids Contained in Microencapsulated Chili Extract

The aim of this work was to evaluate the effects of storage temperature and water activity on degradation of carotenoids contained in microencapsulates of non-aqueous extracts from chili (NAEC). Total carotenoids content and adsorption isotherms of microencapsulated NAEC in a 1:1 weight ratio with gum Arabic-maltodextrin DE 20 (GA 50%–MD50%) were determined at 25, 35, and 40°C. The isotherms were fitted using the Guggenheim-Anderson-de-Boer model and their enthalpies and entropies, both differential and integral, were estimated by the Clausius-Clapeyron method. The minimum integral entropy was considered as the point of maximum stability at which water less readily participates in degradation reactions. Zones of minimum integral entropy were found between 7.56–8.30, 6.10–6.95, and 5.15–6.04 kg H₂O/100 kg dried solids, corresponding to water activity (a_w) of 0.210–0.239, 0.238–0.277, and 0.262–0.313 at 25, 35, and 40°C, respectively. Total carotenoids content (CT) degraded over time, but degradation of carotenoids was lower in microcapsules stored at 25°C than those stored at 35 or 40°C. The morphology of microcapsules was altered at a_w > 0.6, including swelling of the polysaccharide matrix was presented, and possible subsequent dissolution of the wall material, which indicates a high rate of carotenoid degradation. When microencapsulated NAEC were storage between 0.2–0.6 of water activity, the highest glass transition temperatures were achieved. In this range, the wall materials of the microcapsules suffer less microstructural modifications, associated with the minimum level of degradation of carotenoids. Sometimes, in this water activity range, the zones of minimal entropy were observed.