Mushroom dehydration in a hybrid-solar dryer

Abstract

Mushrooms (Paris variety) were dehydrated in a hybrid solar dryer (HSD) provided with a 3m2 solar panel and electric resistances. Mushrooms were cut in 8mm or 4mm 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°C). At the outlet of the solar panel the air temperature raised between 2 and 20°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 (Xc), 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°C showed that in less than 30min rehydrated mushrooms reached a moisture content of 0.8 (wb).Effective diffusivity (Deff) was estimated by the Simplified Constant Diffusivity Model (SCDM), and it ranged between 6E−10 and 40E−10m2/s, with R2 higher than 0.98, agreeing with literature. The adjustment of experimental drying kinetics with the empirical Page’s model resulted in R2 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.