Freeze-drying characteristics of strawberries

Drying kinetic, as well as color and volume variation. of whole and sliced strawberries were investigated after freeze-drying under various temperatures (30, 40, 50, 60 and 70degreesC. Dehydration time increased proportionally to the thickness of the product and heating plate temperature markedly reduced it. Freeze-drying caused a pronunciation in red color of strawberries. A decrease in hue angle by 22.5% (skin) and by 42.4% (pulp) was noted. with no significant effect of Freeze-drying temperature up to 70degreesC. The strawberries had a volume reduction of 8% (whole) and 2% (sliced) due to freeze-drying although the level of shrinkage was also independent of freeze-drying temperature. However, the percentage of collapsed strawberries increased with process temperature. At heating temperatures higher than 50degreesC, the strawberry dry layer temperature was higher than the estimated glass transition temperature of dried fruit, increasing the risk of collapse.