Rheological properties and colour evaluation of papaya during osmotic dehydration processing

Abstract

Osmotic dehydration of papaya pieces using sucrose solution with additives was studied. Four types of solutions with different concentrations of sucrose, citric or lactic acid and sodium lactate or calcium chloride were employed. Water loss and sugar gain were fitted to a Fick mathematical model and showed that mass transfer increases as temperature or soaking solution concentration increases. The presence of calcium chloride in the osmotic solution seemed to improve sugar impregnation during the osmotic process. The results showed that high temperatures with the combined use of lactic acid and sodium lactate promoted faster water activity decay. The effect of osmotic dehydration on the colour parameters (luminosity and chroma) and rheological properties (stress at rupture and relaxation time) were investigated. Chroma values increased, denoting colour intensification along the process. Luminosity showed a slight increase for samples treated with CaCl 2, but for the other treatments lightness decreased in the first hour and returned for the initial values along the process. Calcium chloride showed to be effective in reinforcing tissue structure, presenting stress at fracture values for dehydrated papaya with calcium salt around three-fold higher than for other treatments. Processing at 50 °C with sodium lactate prevented over-softening of the tissue during the whole process, with greater water activity reduction.