Estudo da secagem de tomate (Lycopersicon esculentum L.) com pré-tratamento osmótico: efeitos do epicarpo e do encolhimento.

Abstract

The objectives of this present work were: 1) to study the kinetics at the pretreatment of tomatoes, submitted to an osmotic solution, with different concentrations of sodium chloride and sucrose o f 5:0,4; 10:0,4 and 15:0,4%. 2) to obtain the thin layer drying curves of tomatoes with an osmotic pretreatment and without an osmotic pretreatment, considering the shrinkage effects, at the drying temperatures of 60, 70, 80 and 90°C. 3) to determine the influences of the tomatoes epicarp on the mass transfer rate during the osmotic pretreatment and drying process. 4) to detenriine the coefficients o f the equation proposed by Page and the analytical solution o f Fick. 5) to determine the shrinkage coefficients using the Uniform and Central drying models. The drying curves were studied by analyses o f non-linear regression, using the software STATISTICA 5.0. According to the obtained results one can conclude that: 1) Considering the drying kinetics o f the tomato during the osmotic pretreatment in the concentrations of sodium chloride and sucrose in the proportions o f 5:0,4; 10:0,4 and 15:0,4%, the equation proposed by Page adjusted better to the experimental data than the Fick's equation, using until the sixth term o f the series. Considering the drying kinetics o f tomatoes without the shrinkage phenomenon at the temperatures of 60, 70, 80 and 90oC with epicarp and without epicarp and also without osmotic pretreatment and with osmotic pretreatment, it was concluded that: the) o f the two proposed equations, once again Page presented better results, when adjusted to the experimental data, than the Fick's equation, using six terms o f the series. Considering the drying kinetics o f the tomatoes, including the shrinkage effects at the temperatures of 60, 70, 80 and 90°C with epicarp and without epicarp and also without osmotic pretreatment and with osmotic pretreatment, it was concluded that: the equation proposed by PARK (1987), where the phenomenon of the shrinkage is included in the moisture rate did not present concrete results in this specific case of the tomatoes dried with epicarp and/or without epicarp. In the case o f the shrinkage, o f the two models (Uniform and Central) studied, the equation that best expresses the coefficient o f shrinkage o f the tomato, in the studied conditions, it is the Uniform model. For tomatoes dried at temperatures of 80 and 90°C, there was a migration o f salt to the surface in all the studied osmotic concentrations as well as for the tomatoes without epicarp, not recommending the drying at those conditions. As a final conclusion in the studied conditions the tomato should be dried at the temperatures of 60 or 70°C and with an osmotic pretreatment of sodium chloride-sucrose of 10:0,4% or 5:0,4%.