In this study, thin slices (diameter 22, thickness 4 mm) of apple (Golden delicious), were dried by either hot air or combined method (coating, hot air and microwave drying). In order to prevent undesirable enzymatic browning reactions, blanching (with hot water at 80°C for 1min) was used. To produce porous and puffed products samples were coated by starch, pectin and CMC solution (2%w/w) containing CaCl2 (1%w/w). Using blanching, coating, hot air (75°C, 1m/s) drying and microwave (300 W, 10s) assisted hot air drying, porosity and brittleness was observed in the final product. It was observed that using the above mentioned drying method, the porosity of samples can be increased by about 19.38 and 15.38% (according to their coating material), as compared with hot air dried samples. Adding CaCl2 to coating solution, can increase porosity of samples by about 18.31%. Investigation by SEM microscopy showed that coated samples by starch and pectin along with CaCl2 exhibit completely porous structure while microwave heating causes some cellular damages. Using hot air drying leads to a significant amount of shrinkage.
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