Optimization of microwave assisted multilayer drying of bittergourd

Abstract

Bittergourd rings were dried to a moisture level of 0.1 g water/g dry matter using a multilayer-cummicrowave drying technique. Response surface methodology was used to optimize the drying conditions based on specific energy consumption and quality of dried bittergourd viz. change in color, rehydration ratio, shrinkage ratio, ascorbic acid content and hardness of texture. A second-order polynomial model fitted well to all responses and high R2 values (>0.8) were observed in all cases. The change in color of the dried bittergourd was found higher at high microwave power and exposure time combination, whereas 80% retention of ascorbic acid and maximum rehydration ratio was observed at 504W. The specific energy consumption decreased with an increase in microwave power due to reduced drying time. The optimum operating conditions for drying bittergourd were PL: 504W and ET:24s, resulting in dried product with maximum rehydration ratio, ascorbic acid retention, overall acceptability, minimum shrinkage ratio, hardness and color change. The overall desirability was 0.725. Use of microwave application in the last stage of drying saved 39% energy. Therefore, microwave-assisted drying should be considered for improved heat and mass transfer and produce dried bittergourd with better quality.