Effect of osmotic dehydration time on hot air drying and microwave vacuum drying of papaya

Abstract

This study was subjected to hot air drying (70°C) and microwave vacuum drying (1200 W and 13.3 kPa) of osmotically dehydrated papaya. Osmotic dehydration was carried out in sucrose solution (65% (w/w)) at 40±2°C for 1–4 h. The ratio of papaya to the solution was 1:5. In the hot air drying, an increase in osmotic dehydration time from 1 to 4 h decreased hardness, lightness (L* value) and chroma (C* value) of papaya significantly (p<0.05).In the microwave vacuum drying, a similar trend of hardness reduction was observed when the osmotic dehydration time was increased. However, the microwave vacuum dried papaya had lower hardness and chroma than the hot air dried samples. Hue angle (°h) of the microwave vacuum dried papaya was in the range of 48.55–50.32 whereas that of the hot air dried samples was in the range of 0.83–0.91. Regarding the scanning electronic micrograph, increasing osmotic dehydration tim could reduce the shrinkage of the hot air dried papaya and reduce the degree of damage in the microwave vacuum dried papaya. Comparing between both drying conditions, the microwave vacuum drying yielded the fine and porous structure, whereas, the hot air drying yielded the dense structure. Therefore, rehydration rate constant of the microwave vacuum dried papaya was significantly higher than that of the hot air dried samples (p<0.05).