Button mushroom (AgaricusbisporusL.) is extensively produced and consumed in the world. They are more perishable due to their high moisture content. Due to its short shelf-life, the mushroom is usually dehydrated for preservation. Hot air dried mushrooms result in losses in nutrients, colour degradation and deformation in structure. To overcome these problems, freeze-drying of mushroom slices was investigated. White button mushrooms after cleaning were vertically cut into 2, 4, 6 and 8 mm thick slices. Sliced mushrooms were frozen at −20 °C and then subjected to the freeze-drying at various heating plate temperatures of 10, 20, 30 and 40 °C. The effect of slice thickness and heating plate temperature on physicochemical properties like rehydration, porosity, firmness, water activity, colour, ascorbic acid, protein and microbial properties like total bacterial, yeast and mould were evaluated during the storage. Increase in the storage period resulted in decrease in porosity (73.25%), colour L* value (48.12), firmness (0.98 N), rehydration ratio (4.04), ascorbic acid content (14.47 mg/100 g) and protein content (19.15%), whereas the water activity (0.412) increased with the storage period. This may be due to the absorption of moisture during storage. Microbial analysis indicated by yeast count, mould count and total plate count was nil during the first three weeks of storage, whereas in the fourth week negligible growth was observed. So it is concluded that this may be due to the low water activity of stored mushroom slices.
Evaluation of Process Conditions for Ultrasonic Spray-Freeze Drying of Transglutaminase
