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KMID : 1024619980180020164
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Food Science of Animal Resources
1998 Volume.18 No. 2 p.164 ~ p.175
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Influence of Freezing Process on the Change of Ice Crystal Size and Freeze-Drying Rate in a Model System
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Byun Myung-Hee
Lee Seong
Choi Mi-Jung
Min Sang-Gi
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Abstract
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The objective of this study was to investigate the effects of freezing rate on ice crystal size and freeze-drying rate. Our experiments were carried out with self-manufactured freeze-dryer. Gelatin gels (2% w / w, 8020mm) were frozen unidirectionally (Neumann’s model) from the bottom at -45, -30, -20, and -15 and followed with freeze-drying. Under the upper conditions we measured freezing rate and the change of temperature and pressure during freeze drying. Freeze-dried gelatins were cut horizontally into 5 mm thickness from the bottom and measured their pore sizes. Also freeze-drying rate(primary drying) is estimated by measuring the temperature of sample and pressure of vacuum chamber. During freeze-drying, profiles of pressure and temperature were shown constant tendency regardless of freezing temperature and we could expect the end-point of freeze drying by considering pressure and temperature together. In temperature profiles, the point which temperature increased significantly was observed during freeze-drying. There is no relationship between freeze temperature and drying rate of primary drying in our model system. As freezing temperature increased, ice crystal size(X*) which correspond to 63.2% of cumulative frequency was increased and at the same freezing temperature ice crystal size(X*) was decreased with distance from the bottom of the sample. Freezing conditions have a strong influence on the quality of the final freeze-dried products in freeze-drying system.
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KEYWORD
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freezing rate, ice crystal size, freeze-drying rate
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