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Watermelon is a highly perishable fruit with a niche for majority of microrganisms. It comprises of 91% water and hence it is very difficult to preserve watermelon based products by application of conventional means. Ohmic heating, also known as Joule heating is an electrothermal technique of processing. In this study, the effect of ohmic heating on the electrical conductivity, pH and colour of the watermelon juice at various voltage gradients (10-23.33V/cm) was investigated. The change in the pH and colour of the watermelon juice during storage was studied. The bubbling of juice was observed above 60°C at all voltage gradients. As the voltage gradient increased the time required to reach the desired temperature decreased. The electrical conductivity was observed to increase with increase in temperature. Linear model gave the best fit to the electrical conductivity of watermelon juice. The change in pH and colour has increased with increase in voltage gradient, ohmic heating time and storage period. Ohmic heated watermelon juice showed better retention of physicochemical properties when compared to conventional heating. [ABSTRACT FROM AUTHOR]

Studies were conducted to use ultrasound treatment in watermelon (Citrulus lanatus) rind as a pre-treatment prior to osmotic-drying. A comparison with the conventional heating as pretreatment prior to osmotic-drying was also carried out. Effects of treatment time (10, 20 and 30 min in ultrasound and 1, 2 and 3 min in conventional method), sugar concentration (40, 50 and 60°Brix) and immersion time (0 - 6 h) on water loss and solid gain in watermelon rind were studied. Second order regression equations describing the effects of these factors on the water loss and solid gain were developed. Results shows the maximum water loss and solid gain of 81 and 46%, respectively for the watermelon rind treated for 30 min under ultrasound and immersed in 60°Brix solution for 6 h. In conventional pretreatment the maximum water loss and solid gain in water melon rind to the tune of 73 and 59%, respectively was achieved on treating the water melon rind for 3 min and immersed in 60°Brix solution for 6 h. The combined process (ultrasound pretreatment and osmotic-drying) was optimized for the operating conditions that minimize total processing time. [ABSTRACT FROM AUTHOR]