Color, Texture, Rehydration Ability and Phenolic Compounds of Plums Partially Osmodehydrated and Finish-Dried by Hot Air

Abstract

The aim of this study was to analyze the influence of the drying process by combined methods. Osmotic dehydration was performed using glucose or sorbitol solutions at different concentrations (40 or 60 °Brix), temperatures (25 or 40C) and two fruit-to-syrup ratios (1:4 or 1:10). Hot air drying was performed at different temperatures (60, 70 or 80C). Dried plums were evaluated in terms of color, texture, rehydration ability, phenolic compounds (total phenols, flavonoids) and water activity. The color was analyzed through two methods: colorimeter and image analysis. The evaluations showed a decrease in luminosity and an increase of reddening due to browning originated during the drying process. The image analysis was the most appropriate to evaluate the changes in color. Firmness of plums increased in relation to fresh fruit and was more evident at higher drying temperature. High drying temperatures provoked a collapse of the plum structure, which hindered water absorption in the rehydration process. The phenolic compounds in plums were conditioned by the drying temperature; the content of phenols and flavonoids was higher when they were dried at 70C. Plums osmodehydrated in sorbitol 60% w/w, with a fruit/syrup ratio of 1/10, at 25C and air dried at 70C obtained a high degree of dehydration and best maintained quality attributes.