FREEZE-DRYING CHARACTERISTICS OF STRAWBERRIES

ABSTRACT

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 70°C). 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 70°C. 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 50°C, the strawberry dry layer temperature was higher than the estimated glass transition temperature of dried fruit, increasing the risk of collapse.

Keywords:

• Collapse
• Color
• Glass transition temperature
• Shrinkage
• Small fruits

ACKNOWLEDGMENTS

The authors would like to thank the NSERC (Natural Sciences and Engineering Research Council of Canada) and FCAR (Formation de Chercheurs et l’Aide à la Recherche de Québec) for their financial support.