Effect of osmotic pretreatment on quality characteristics of edible button mushroom during air drying

Osmotic dehydration is a new method to reduce the moisture content of food. In this method, moisture is reduced by direct contacting food with salt and sugar concentrated osmotic solutions through the cell membrane based on natural and nondestructive osmosis. Application of osmotic dehydration prior to hot air drying improves product quality. In this study the effect of osmotic dehydration prior to hot air drying on the quality properties of button mushroom was studied. Sliced mushrooms were immersed in sodium chloride solution with concentrations of 5 and 10%, sample to solution ratio of 1:20 at temperatures of 30 and 40 °C for 60, 120, 180 and 240 min. Optimal osmosis condition based on the highest WL/SG were found to be a temperature of 40 °C and a concentration of 5% and an osmosis time of 120 min. Samples followed by air drying at 60°C to a final moisture content of 0.2 (g water per g dry matter). Shrinkage, rehydration ratio and color parameters were measured. Results showed increasing temperature, osmotic solution concentration and osmosis time led to an increase in WL and SG. Osmotic pretreatment reduced shrinkage, rehydration ratio and "L" color parameter in hunter lab system; but had no significant effect on overall color change and "a" and "b" values.