Air drying kinetics and quality characteristics of oyster mushroom (Pleurotus ostreatus) influenced by osmotic dehydration

Abstract

The study on osmotic pretreatment of oyster mushrooms was carried out in order to remove the moisture prior to further mechanical drying.  Three salt concentration level (10, 15 and 20 g/100 g), two temperature levels of osmotic solution (30 and 45°C) and constant solution to mushroom ratio of 10 (w/v) were selected and the observations on water loss and solid gain were taken at an interval of 30 min up to 300 min.  The osmotically pretreated samples were further dried up to its equilibrium moisture content in a tray drier at 60°C and experimental data were fitted successfully using Page and Henderson & Pabis model.  The osmo-convective dehydrated samples were evaluated for its quality parameters i.e. color (L, a, b, ∆E, C* and h°), rehydration ratio and sensory attributes (flavor, appearance, texture and overall acceptability).  The water loss from and solid gain by the mushroom sample increased non-linearly with the duration of osmosis at all concentrations and both were higher in the initial period of osmosis than the later period.  Further, both increased with increasing salt concentration and osmosis solution temperature.  Samples pretreated in salt of 20 g/100 g at solution temperature of 45°C showed lower drying rate due to deposition of salt molecules on outer surface of mushroom tissues.  The analysis of variance (ANOVA) revealed that among the osmosis pretreatment variables, the concentration has the most significant effect on all the selected quality parameters whereas the interaction of solution temperature and salt concentration witnessed maximum effect on color and rehydration ratio.

Keywords: oyster mushrooms, osmotic dehydration, water loss, solid gain, drying, quality