Mushroom dehydration in a hybrid-solar dryer

Mushrooms (Paris variety) were dehydrated in a hybrid solar dryer (HSD) provided with a 3 m(2) solar panel and electric resistances. Mushrooms were cut in 8 mm or 4 mm thickness slices. At the outlet of the tray dryer 80-90% air was recycled and the air temperature was adjusted to the pre-defined levels (50 or 60 degrees C). At the outlet of the solar panel the air temperature raised between 2 and 20 degrees C above the ambient temperature, depending mainly of solar radiation level. Temperature, slices thickness and air recycle level had statistically significant effects on critical moisture content (X-c), as well as on the time necessary to reach a moisture content of 0.1 (wb). The color parameters of dehydrated mushroom indicate a notorious darkening, in all runs. Rehydration assays at 35 degrees C showed that in less than 30 min rehydrated mushrooms reached a moisture content of 0.8 (wb). Effective diffusivity (D-eff) was estimated by the Simplified Constant Diffusivity Model (SCDM), and it ranged between 6E-10 and 40E-10 m(2)/s, with R-2 higher than 0.98, agreeing with literature. The adjustment of experimental drying kinetics with the empirical Page's model resulted in R-2 higher than 0.997. Finally, the input of solar energy resulted in 3.5-12.5% energy saving. These values could even be improved by increasing the agro-product load in the HSD. (C) 2013 Elsevier Ltd. All rights reserved.