Background and Objectives: Osmotic dehydration is recommended as preliminary process in food drying. Using of sucrose and glucose sugars, as osmotic agent, may lead to lower nutritional quality in final product. In this study, the effects of replacement of these conventional sugars with sorbitol and fructose, that have higher nutritional quality, on osmotic dehydration efficiency and quality properties of dried Shahroodi grape (raisin) were investigated.

Materials and Methods: In this research, in first, all samples (15 treatments at three replicates) coated with carboxymethyl cellulose based solution (1%). Five types of osmotic solutions (including sucrose, glucose sorbitol fructose and fructose- sorbitol) in different concentrations (55, 45 and 35%) were used to select the optimum osmotic solutions based on the maximum water loss and dehydration efficiency coefficient and minimum solid gain. The control and pretreated samples were then dried in the oven (air temperature of 80 °C and air velocity of 1.5 m/s) and the effects of coating and osmotic dehydration pre-treatments on the quality of raisins, including shrinkage, rehydration ratio, color, textural properties, vitamin C , salt and acid contents, were investigated.

Results: The fructose based osmotic solution showed significantly higher osmotic dehydration efficiency. In addition, using fructose and sorbitol osmotic solutions caused to higher maintaince of vitamin C and lower total color change in comparison to glucose and sucrose based osmotic solutions. However, there were not significant differences in texture hardness and rehydration properties among samples treated by different osmotic solutions

Conclusions: The result of this study shows that osmotic solution of fructose and fructose- sorbitol can be successfully used in osmotic dehydration of Sharoodi grapes.

Keywords: Osmotic dehydration, Grape, fructose, Sorbitol