Effect of osmotic dewatering on apple tissue structure

Abstract

Apple cubes were subjected to osmotic dehydration in 61.5% sucrose and changes in tissue structure were examined in light microscope. Fixed and embedded in raisin 3 μm thick slices were analysed and indices characterising apple tissue structure were calculated with computer image analysis. It was found that osmotic dehydration affects size and shape of cells, and in consequence changes shape and dimension of intercellular spaces. No broken cell walls were found in osmosed tissue. Osmotic treatment increased the share of small cells in tissue and moved shape factor toward smaller values. There was a difference in response of cells to osmotic stress dependent on the cell location. Cells, which are in contact with intercellular spaces reacted to osmotic stress in different way than those surrounded by other cells. Shrinkage of cells and deformation of cell walls caused increase of circumference of intercellular spaces. The increase was more than 30% until 120 min of osmosis. Moreover, intercellular spaces became more irregular than those did in raw apple. Further osmotic treatment caused substantial increase of small intercellular spaces, which was probably due to detachment of some cells and splitting of middle lamella. This observation suggested that prolonged osmotic dehydration could disintegrate apple tissue and destroy its continuity.