Abstract
In order to study the dehydration of vegetables in saline solutions, the osmotic pressure of twenty-seven vegetables and saline solutions were measured. Subsequently, dehydration of the Japanese radish, daikon, was kinetically analyzed in the solutions of different salt concentrations. The structure of the radish membrane was also observed using a scanning electron microscope (SEM). The results were as follows. The mean osmotic pressure of leaf, fruit, and root vegetables were 4.25, 7.47, and 9.62 atm, respectively. Root vegetables showed the highest osmotic pressure, while leaf vegetables showed the lowest. The dehydration process of the radish followed four stages: initial dehydration, first equilibrium period, reduction period and second equilibrium. Observations using SEM showed that the cell membranes of radish shrank and that some of the cell contact sections were torn apart by the dehydration. The dehydration process of the radish in different salt concentrations followed first-order kinetics and the rate constants were in the order of 10-2 (min-1), and the rate constants were also proportional to the surface area of the sample. From temperature dependence, the activation energy of the dehydration process was calculated at 3.5 kcal/mol. The thermodynamic properties of the process were also calculated using Eyring's equations. The activation free energy, activation enthalpy, and activation entropy were 21 to 23 kcal/mol, 3.0 kcal/mol, and-62 to-64 e.u., respectively. The activation energy and the activation free energy were rather small values and the activation entropy had negative values.
