Effects of pretreatments and drying methods on dehydration of mushroom

Dehydration of button mushrooms (Agaricus bisporus) and oyster mushrooms (Pleurotus flavus) were carried out with various pretreatments like blanching, blanching followed by soaking in potassium metabisulphite (KMS), fermented whey, curds, etc. and dried in different dryers viz, hot air cabinet dryer, fluidized bed dryer, vacuum dryer and microwave oven. The drying times were less in the case of oyster mushrooms (7200–8100 s) compared to button mushroom (8700–10800 s) with cabinet drying. For both oyster and button mushrooms using pretreatment by dipping in curds or fermented whey the time of drying was less compared to other treatments in all types of dryers. The effect of drying methods was expressed by a polynomial equation and the regression coefficients were determined. The time taken for drying from 7.5% (db) moisture to 2.0% (db) was in the order of vacuum dryer > cabinet moisture dryer > fluidized bed dryer > microwave oven. However, fluidized bed drying seems to be a promising method for drying mushrooms, when comparing the lower drying time and good quality products to the faster microwave drying. The diffusion coefficients evaluated were also found in the same order. In case of oyster mushroom, the diffusion coefficient was found maximum (469.7 × 10−6 m2/s) for the whey treated microwave dried mushroom and minimum (2.609 × 10−6 m2/s) for the control cabinet tray dried sample. The diffusion coefficient was maximum (331.02 × 10−6 m2/s) for the blanched button mushroom dried by microwave drying and minimum (0.3225 × 10−6 m2/s) for the control sample dried by vacuum oven.