Abstract
In addition to liquid foods and semi-solid foods, agricultural products such as vegetables and fruits are currently being dried and distributed to large food processing companies. The purpose of such food drying processes is not only to reduce the volume and weight of the products but also to improve the product stability (shelf life) whereas the product quality must be maintained during and after drying. Pre-drying treatments such as addition of sugars are needed for vegetable drying in order to avoid damages to tissue structures. In this study the water desorption behavior was investigated for various sugar solutions and vegetables. The desorption isotherms and water diffusion coefficients were determined by isothermal desorption or drying experiments. Most isotherms were well described by the Guggenheim-Andersen-de Boer (GAB) equation. The temperature dependence was different from food to food. Especially disaccharides such as sucrose showed a significant increase of the equilibrium water content at a given water activity (Aw) with lowering temperature. The water diffusivity of sucrose also decreased much more with lowering temperature compared with other food products. The results have shown that all pre-treatments are very effective at 50°C. Pre-treatments with sugar solutions increased drying rate either in carrot or potato drying process. Dipping in sugar solutions of samples decreased the equilibrium water content. The apparent diffusivity values for all potato samples were higher than those for carrot samples. The apparent diffusivity increased with treatment of sugar solutions in all samples. Untreated and blanched samples did not shrink markedly compared with samples treated with sugar solutions. In addition colors of treated samples with sugar solutions are visibly better than untreated and blanched samples.
