Desidratação osmótica de abóbora com uso do pulso de vácuo: otimização e cinética

Abstract

For being a perishable fruit the pumpkin (Cucurbita moschata Duch.) needs postharvest preservation techniques in order to increase their shelf life. The process of osmotic dehydration (OD) is based on the reduction of the available water in food by soaking it in concentrated solution. It is believed that the efficiency of OD can be further improved by using vacuum pulse (PVOD) at the beginning of the process. Therefore, the objective of this work was the optimization of osmotic dehydration process and vacuum pulse use through experimental design by evaluating both the quality parameters of previously bleached pumpkin slices and their kinetic curves. On the first stage of this work, the study was performed according to the Plackett-Burman design (PB) with 12 trials for the screening of variables and to determine the best levels to optimizing the process. The independent variables were: temperature, NaCl and sucrose concentration in the immersion solution, pressure and vacuum pulse time. The following quality parameters were evaluated: water activity (Aw), potential hydrogen (pH), shrinkage (E), water loss (WL), solid gain (SG) and total color variation (∆E). In the second stage, the study was outlined in response surface methodology by central composite rotational design (DCCR) with 28 trials using statistically significant independent variables in the first stage. The process was optimized using the surface response methodology in regard to the desirability. In the last stage, PVOD kinetics was performed in which samples submitted to the best treatment of the process were dehydrated, followed by the construction of parameter curves as a time function. Further analyses towards the behavior of carotenoids, texture, structural characteristics and the effective diffusivity were made. The results obtained in the first stage showed that the temperature was not statistically significant in the process. In the second stage, the following optimum conditions of the process were obtained: 17.5% of the NaCl concentration, 50% of the sucrose concentration, 160 mbar of pressure and 10 minutes of the vacuum pulse time. Under these conditions, the lowest Aw (0.74), the highest WL (71.0%), lowest incorporation of sucrose (3.77%), pH from 5.75 and 48.07% of shrinkage were obtained. The SG, the incorporation of NaCl and the color parameters were not statistically influenced by the PVOD of pumpkin slices. For the last stage, the kinetic curves of quality parameters showed similar tendencies as reported on literature, and the coefficients of effective diffusion reflect the influence of the variables of the process in the kinetics of mass transfer. In addition, the PVOD favored the maintenance of the pumpkin slices’ color, initial content of carotenoids, texture characteristics and microstructure.