Rate of carotenoid degradation in dehydrated carrots

This work was focused on dehydrated carrots with the aim to study: a) the water sorption properties, and b) the rate of carotenoid degradation as a function of water activity. Freeze-dried carrots from blanched and not blanched batches were placed in air-tight glass jars containing saturated salt solutions with water activity ranging from 0.052 to 0.75, at 40°C. The equilibrium moisture, water activity, and carotenoid content were analysed at different storage times. Results showed that the adsorption isotherm fitted the Guggenheim-Anderson-de-Boer (GAB) equation (R2 = 99.65%). Estimated monolayer water activity was 0.33 (confidential limits at 95%: 0.26 and 0.38). α- and β-Carotene contents decreased in all dehydrated carrots following pseudo-first-order kinetics, with rate constants ranging from 0.031 to 0.374 days-1. Similar rate constants were found between α- and β-carotene. In all carrot batches the rate of carotenoid degradation was at a minimum within the water activity range 0.31 - 0.54. Below and above this range the rate of carotenoid degradation increased significantly. Blanching resulted in a higher initial carotenoid content, but it accelerated carotenoid decrease during storage of dehydrated carrots. Based on these results we concluded that two strategies could be useful to increase carotenoid stability during storage: a) the development of intermediate moisture carrots (water activity in the range 0.31 - 0.54); b) the identification of protective factors that can increase carotenoid stability at water activity above 0.54. Both criteria should be combined with optimised packaging conditions, which reduce exposure of product to air and light during storage.