Effects Of Microwave And Ultrasound Assisted Osmotic Dehydration At Different Condition On The Quality Of Semi-Dried Pumpkin Slices

Abstract

Pretreatments applied before drying have been proposed as an effective method to improve the quality of dried fruit samples. In this study, the effects of different pretreatments (ultrasound and microwave) combined with osmotic dehydration on semi-dried pumpkin slices were evaluated. Samples were treated with ultrasound (USOD) at different temperature (30oC, 40oC, 50oC) and different periods of time (30, 60, 90 minutes) while microwave (MWOD) at different powers (240 W, 400 W and 560 W) during 30, 60 and 90 seconds. USOD-50oC-30min and MWOD-560W-60s were used as the most optimal conditions in this research based on the highest result of WL/SG ratio. The Two-term model was used to describe the drying process of pumpkin slices. USOD and MWOD showed effectiveness in significantly shortening drying time to 499 and 510 minutes, respectively. Furthermore, they also showed positive effects on improving product shrinkage, hardness and color. This leads to good reviews for the product by panelists in the sensory analysis. However, significant losses (p<0.05) of nutrients (total phenolic, antioxidant and carotenoids content) compared to non-treated samples were also observed when pretreatment methods were applied. Scanning electron microscopy (SEM) technique was used to analyze the structural changes that are responsible for the differences mentioned.