The effects of different freeze-drying processes on the moisture content, color, and physical strength of roses and carnations

Freeze-drying is a relatively new preservation process for the preserved plant material industry. However, optimum freeze-drying procedures have been determined for very few flowers. This study evaluated the effects of different freezing times and vacuum-drying temperatures on color, moisture content, and stem and petal strengths of roses and carnations. Strength/stiffness was determined via force-deformation curves. The moisture content of freeze-dried flowers determines their longevity, and fewer changes in shape and color increases their aesthetic value. Vacuum-drying temperatures had more effect on the flowers than freezing time. Lower vacuum-drying temperatures resulted in flowers with color closer to fresh and control flowers, while higher vacuum-drying temperatures resulted in lower moisture contents and stronger/stiffer petals but more changes in color. (C) 2000 Elsevier Science B.V. All rights reserved.