Infrared Heating - A New Green Technology for Process Intensification in Drying of Purslane Leaves to Reduce the Thermal Losses

Abstract

The drying or dehydration of foods is highly important method for the food industry and offers many possibilities for ingredient development with lesser water activity and products with longer shelf life to consumers. The principle of this process is reducing the water content in order to avoid or slow down food spoilage by microorganisms. But foods being biological in composition the contents are more sensitive to heat, as conventional drying methods (conduction/convection) takes longer duration for drying, probability of losing some nutrients is very high. Using an alternative thermal source like infrared heating (radiation) we can reduce the losses during drying by decreasing the process time. Heating by infrared radiation has advantages over conventional heating methods, including time of heating, uniformity in heating, less thermal losses, no migration of solute in food matrix, convenience in handling and operation, and less energy consumption. This present study emphasizes on aspects of infrared heating and its higher drying rates, in turn lesser drying times of purslane leaves and possibilities of reducing the nutrient losses (iron, calcium) and retention of colour using a graphical representation in comparison with conventional tray drying method at 50 °C, 60 °C and 70 °C. In tray drying the duration of drying period decreased from 990 to 270 min, where as in infrared drying the duration of drying decreased from 100 to 35 min when the temperature of drying was altered from 50 °C to 70 °C. With the change in the drying temperature from 50 °C to 70 °C, iron content decreased from 1.599 mg to 1.338 mg per 100 gm and calcium content decreased from 61.23 to 52.56 mg per 100 gm during tray drying where as in infrared drying iron content decreased from 1.78 mg to 1.49 mg and calcium content decreased from 64.17 to 58.44 mg per 100 gm of sample. With the increase in the temperature, brightness decreased and the samples became lighter. The greenness of the samples decreased and yellowness of the samples increased with the increase in the temperature. Infrared radiation could able retain more color than the conventional method of tray drying.