Effect of Air Temperature and Pre-treatment on Color Changes and Texture of Dried Boletus edulis Mushroom

In the present work, the effects of drying air temperature and pre-treatment on color changes and texture of Boletus edulis (Bull.: Fr.) mushrooms were investigated during convective drying. The drying experiments were conducted in a laboratory hot-air dryer at temperatures of 50, 60, and 70 degrees C under thermal (water or steam blanching) and chemical (solution of potassium metabisulfite or citric acid) treatments. Changes in color were evaluated by the CIE-LAB color system and the experimental color parameters (L* a* b*) were fitted to a first order kinetic model. Values of total color difference (Delta E*), hue angle (h*), and chroma (C*) were also calculated. The texture of dried mushrooms was measured by an Instron texture analyzer and expressed as hardness. The model fitted the experimental a* and b* values sufficiently. The results showed that during convective drying, lightness decreased slightly while yellowness and redness increased. Chemical pre-treatments did not influence the color of mushrooms positively while blanching caused intensive color deterioration. Moreover, the Delta E* value could contribute to the assessment of color change effectively. Hardness increased as drying proceeded and was found to be greater at higher temperatures. Mushrooms subjected to water or steam blanching were harder in texture. A temperature limit of 60 degrees C is imposed for the dehydration of B. edulis mushrooms. Thermal treatment prior to drying is not recommended for B. edulis mushrooms when color and texture are desirable quality criteria.