Evaluation of ultrasound pretreatment and drying methods on selected quality attributes of bitter melon (Momordica charantia L.)

Recently, numerous attentions have been drawn to bitter melon (Momordica charantia L.) processing due to its outstanding pharmacological properties. Fresh and ultrasound pretreated bitter melon slices were subjected to hot air drying (HAD) and radio frequency assisted hot air drying (RFHAD) in this study. Quality attributes of the dried samples were compared in terms of moisture content, water activity, glass transition temperature, color, rehydration ratio, and content of chlorophyll, ascorbic acid, and total phenolic. Compared with HAD process, results showed that the use of ultrasound pretreatment and RF heating accelerate water loss during drying processes, and then contribute to a shorter drying time, a lower water activity and higher glass transition temperature of dried samples. It also showed RFHAD had better color exhibition, higher retention of chlorophyll, ascorbic acid, and total phenolic due to uniform heating and shorter drying time. Additionally, ultrasound pretreatment greatly improved the rehydration capacity and total phenolic retention. Therefore, considering the quality attributes and drying time, ultrasound pretreatment and radio frequency drying would be very promising alternatives for food processing.