Desidratação osmótica e secagem de tomate: Influência do pulso de vácuo na incorporação de sódio em soluções ternárias

Abstract

The aim of the present work was to optimize the vacuum pulse osmotic dehydration (PVOD) process using ternary solutions aiming, mainly, to reduce sodium incorporation. The drying of the tomato disks was also investigated. In PVOD the ternary solution used was composed of sucrose and sodium chloride and the independent variables were absolute pressure (Pabs), time of application of vacuum (VT) and water activity of solution (aw). The variables responses were sodium incorporation (INa), water loss (WL), weight reduction (WR), evaluated through a central rotational compound design (DCCR) and optimized by the desirability function. The vacuum time had no significant effect on the independent variables. A reduction in aw of the solution and Pabs caused a reduction in INa and an increase in WL and WR of tomatoes. The optimum conditions obtained were Pabs of 627.5 mm Hg, VT of 15 minutes and aw of the solution of 0.903, which led to higher WL and WR and minimum INa, with values of 30.59%; 24.69% and 63.14 g / kg respectively. Samples pretreated by PVOD under optimum conditions were submitted to convective drying at 50 and 70 °C with air velocity of 0.5 and 1.5 m s -1 . The evaluated parameters were drying time, aw, color and rehydration ratio. The drying kinetics were obtained and adjusted using the Fick model. After drying, samples with a moisture content of 19 kg of wet water kg -1 had aw at safe levels below 0.450. Shorter drying times, greater effective water diffusivity with increasing temperature and drying air velocity were obtained. The Fick model fitted well to the experimental data. The higher drying temperature led to a higher ratio of rehydration. Small variations were observed in the color parameters. Effective moisture diffusivity ranged from 8.16 × 10 -9 to 2.38 × 10 -8 m² s -1 in the temperature range studied. The results demonstrate that the use of vacuum pulse can be recommended to reduce the incorporation of sodium during the osmotic dehydration of tomatoes with ternary solutions.