Effect of pretreatment on color of dehydrated products

The effect of pretreatment on color of convective dried products (namely ap ple, banana, potato and carrot) was investigated. Five different types of p retreatment were taken into consideration; microwave, osmotic, sulfite, wat er blanching and steam blanching. Color characteristics were identified by measuring the color parameters (namely, Lightness (L), Redness (a) and Yell owness (b)) using a Hunter Lab chromatometer. The type of pretreatment was found to significantly affect the three color parameters. In addition, Redn ess (a) and Yellowness (b) were found to follow a first order kinetic model . Untreated dried materials showed an extensive browning, indicated by a si gnificant drop of the L parameter and a corresponding increase of a, b para meters. Osmotically and microwave pretreated samples supressed browning com pared to the untreated samples. In this case, lightness decreased slightly, while a, b increased slightly. Sulfite pretreatment prevented significantl y color deterioration, while water and steam blanching also prevented enzym atic browning during convective drying.