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Abstract
Microwave-osmotic dehydration (MWOD) under continuous medium flow is a new technique with good potential for quality optimization. It combines microwave heating with osmotic dehydration for enhancing moisture transfer rate in the osmotic dehydration process and product quality. This study was carried out to investigate the effects of continuous medium-flow MWOD of apple (Red Gala) cylinders in immersion (MWODI) and spray (MWODS) modes, as well as with conventional osmotic drying (COD) under similar continuous medium-flow (immersion, CODI, and spray CODS) modes. Two temperature–sugar concentration conditions with different contact times were employed to create 24 different test conditions for each of the four methods to test the differences between them. The process was monitored based on changes in moisture content, weight reduction, and solids gain.
The results showed, in general, that the continuous medium-flow microwave-osmotic dehydration under spray mode (MWODS) considerably enhanced the moisture transfer rate from the fruit, leading to a significant increase of moisture loss. For example, at 50°C/50°Brix for 2 h, the moisture loss with MWODS was 34–94% higher than in other methods, whereas the solids gain was 16–46% lower than with the other methods. Overall, MWODS was far more effective than similar techniques in enhancing moisture loss and simultaneously restricting the solids gain.