Effect of pre-treatment on convective drying of tomatoes

Tomatoes of two varieties were dried by convection at 60 degreesC. Skin was removed and quarters of tomatoes were pre-treated either by soaking in CaCl2 solution or by soaking in this solution followed by osmotic dewatering. Another batch of tomatoes was treated by osmosis in hypertonic solution containing sucrose and calcium chloride. Pre-treatment of tomatoes with calcium chloride increased the rates of convective drying and osmotic dewatering as well. Convective drying of pre-treated tomatoes was 20% shorter than that of raw material. Pre-treatment with CaCl2 increased by 20% the amount of water removed during osmotic dehydration and facilitated infiltration of sucrose. Treatment with CaCl2 followed by osmotic dewatering was more effective than osmotic treatment done in the presence of calcium chloride. Rehydration properties of pre-treated and dried tomatoes were poor. It was suggested that interactions of calcium with polymers stiffened the structure, which on one hand improved drying processes, but on the other hand restricted polymer hydration and swelling during rehydration. (C) 2002 Published by Elsevier Science Ltd.