Microwave vacuum drying of osmotically dehydrated mandarin cv. (Sai-Namphaung)

Mandarin [mandarin cv. (Sai-Namphaung)] was subjected to osmotic dehydration prior to microwave vacuum drying. Osmotic solutions were varied using different ratios of sucrose to glycerol (9:1, 7:3 and 5:5 w/w). Because of the decreased moisture content and solid gain during osmotic dehydration, dielectric properties of mandarin were changed significantly (P ≤ 0.05). The osmotically dehydrated mandarin was then dried further using microwave vacuum drying at 4.8 and 6.4 W g−1. Among thin layer models, page model was the best to describe the drying of osmotically dehydrated mandarin. An increase in the microwave power could increase drying rate without significant effect on hardness of dried samples. Nonetheless, the hardness was significantly (P ≤ 0.05) reduced by an increase in the glycerol ratio in the osmotic solution. The increase in microwave power and glycerol ratio significantly (P ≤ 0.05) decreased β-carotene content and thereby affected colour of the dried mandarin.