Effect of osmotic dehydration and ultrasound pre-treatment on cell structure: Melon dehydration

The effect of osmotic dehydration and of ultrasound pre-treatment applied at atmospheric pressure for different lengths of time on melon tissue structure was evaluated. Osmotic dehydration-induced gradual loss of shape of cell wall, disconnection between the cells and breakdown of the tissue. Ultrasound induced the formation of microscopic channels in the fruit structure but did not induce breakdown of the tissue. The changes observed on the structure of the fruit explain the effects of these two pre-treatments on the water diffusivity of the subsequent air-drying step. Osmotic dehydration when carried out for less than 30 min decreases the water diffusivity due to the incorporation of sugar, but increases water diffusivity when carried out for more than 1 h due to the breakdown of cells lowering the resistance to water diffusion. Ultrasound treatment increases water diffusivity due to the formation of microscopic channels which also offers lower resistance to water diffusion.