Drying 2004 – Proceedings of the 14th International Drying Symposium (IDS 2004) São Paulo, Brazil, 22-25 August 2004, vol. C, pp. 2084-2090 2084 VACUUM DRYING OF OSMOTIC DEHYDRATED APPLE SLICES Maria A.Mauro 1 , Sandra M. Monnerat 2 and Alan E. Rodrigues 1 . 1. Institute of Biosciences, Language, and Physical Sciences, Department of Food Engineering and Technology, Rua Cristóvão Colombo 2265, 15054-000 - São José do Rio Preto, SP, Brazil, E-mail: cidam@eta.ibilce.unesp.br 2. School of Food Engineering - FEA, State University of Campinas - UNICAMP, P.O. Box 6121, 13081-970 - Campinas, SP, Brazil. Keywords: Vacuum drying, osmotic dehydration, shrinkage, density ABSTRACT In this work, the effect of the osmotic solution concentration and of the vacuum oven temperature on the specific volume of dried apple slices was studied. Samples pre- treated with 40 and 50% sucrose solutions (0.5, 1, 2 and 3 hr) and dried in a vacuum oven at 50 o C shrunk less than untreated slices or even than the ones treated and dried at 60 o C, which very collapsed. These results obtained by vacuum drying were compared with data determined for slices dehydrated in osmotic solutions (2 hours of treatment) and dried in a hot air dryer (50 and 60 o C, 2 m/s). In this case, the observed drying rate was higher and the slices shrunk less than those dried in vacuum oven, and the shrinking at 50 o C was slightly lower than 60 o C, showing the same trend. INTRODUCTION Dehydration of foodstuffs by immersion in an osmotic solution has received special interest, since it can improve the quality of the final product when used in combination with other processes such as air drying (Karathanos et al., 1995). In osmotic dehydration a foodstuff is immersed in a concentrated solution containing one or more solutes. When used for whole plant tissues, this process is characterized by the large-scale transfer of the certain compounds, especially those of the solvent (such as water), whereas that of others, especially the solute, is limited, due to differential permeability of cellular membranes (Bidwell, 1974). The osmotic dehydration of apple dices prior to air drying, protects the fruit against the adverse effects of heat and oxidation, during drying (Quintero-Ramos et al., 1993). Also, the pre-concentration of apples in sugar solutions reduces, significantly, the effective water diffusivity during air drying, in comparison to non-treated fruit, that may be beneficial in the storage stability and utilization of