Microstructural changes during osmotic dehydration of parenchymatic pumpkin tissue

Abstract

Pumpkin ( Cucurbita pepo L.) fruit was selected to study the microstructural changes of vegetable tissue during osmotic dehydration. Cylinders (diameter: 1.5 cm; length 2.5 cm) of the parenchymatic tissue were dehydrated with 45% (w/w) sucrose solutions at 25 °C. The microstructure of fresh and processed samples was observed using light microscopy techniques. Fresh pumpkin cells showed average values of 0.015 mm 2, 0.469 mm and 0.136 mm for cell area, cell perimeter and cell equivalent diameter, respectively; and 1.288, 0.831 and 0.871 for cellular elongation, roundness and compactness, respectively. The main modifications observed during osmotic dehydration were shrinkage of cells, plasmolysis and folding of the cell walls. These changes led to the decrease of cellular area, equivalent diameter, roundness and compactness; elongation of cells increased whereas the perimeter was maintained essentially constant along the process. The observed changes were not homogeneously distributed in the material, and were dependent on cell location in the sample and on process time. Empirical quadratic functions were used to relate the average cellular shape and size parameters with the dehydration parameters water loss, weight reduction and normalized moisture content. The equations showed a good fit of the experimental data, leading to correlation coefficients ranging 0.93–0.99 and average relative deviations ranging 0.7–2.8%.