Investigating shrinkage corrected drying characteristics, rehydration, color profile and microstructural evolution during solar drying of pineapple slices

The study describes the solar drying characteristics of pineapple slices with incorporation of shrinkage and influence of drying and rehydration on structural alterations, color profile and microstructure. Samples were dried in mixed mode solar dryer at an air velocity of 0.5 m/s, with recorded average solar radiation, ambient and drying chamber temperature of 665 W/m(2), 33 degrees C and 65 degrees C, respectively, from initial moisture content of 89.9% to a final moisture content of 23% in 6.5 h. Samples showed 43.7% higher drying rate and 82.25% lesser moisture diffusivity on consideration of shrinkage. Moisture diffusivity was increased with a reduction in moisture content during drying on ignoring the shrinkage, while it was initially increased and then gradually reduced at later hours when shrinkage effect was considered. The slices showed overall shrinkage of 86.95% during drying but could recover only 35-45.57% of its volume during rehydration. The water absorption and volume recovery were consistently higher at rehydration temperature of 60 degrees C followed by 45 degrees C and 30 degrees C. Solar dried and rehydrated samples demonstrated overall color change of 16.80 +/- 1.15 and 5.87 +/- 2.5-7.56 +/- 1.43, respectively. Scanning electron micrographs of solar dried samples presented collapsed cellular matrix but rehydrated samples showed porous microstructure indicating regaining of honeycomb network. Practical Applications Solar drying is an essential sustainable approach to reduce the tremendous post-harvest losses of fruits and it also offers the advantages of energy cost saving, higher affordability level and greater payback power to farmers. Present study explored the drying characteristics, followed by rehydration characteristics and effect of drying and rehydration on quality attributes of pineapple slices. Therefore, results are helpful for food processors and engineers in optimization of drying and rehydration processes to obtain best quality products, shelf-life extension of perishable fruits. Solar dried pineapple slices will give better returns to farmers. Moreover, dried pineapple can be utilized as dried chips/snacks, powder, etc. and also can be further rehydrated to reconstitute for utilization in different value added food products like ice-cream, cakes, flakes, granules etc.