Influence of Freezing Process on the Change of Ice Crystal Size and Freeze-Drying Rate in a Model System

모델 시스템에서 동결속도에 따른 얼음 결정체의 크기 및 동결건조속도의 변화

  • Byun, Myung-Hee (Department of Animal Products Science, Kon-Kuk University) ;
  • Choi, Mi-Jung (Department of Animal Products Science, Kon-Kuk University) ;
  • Lee, Sung (Department of Food and Biotechnology, Han Seo University) ;
  • Min, Sang-Gi (Animal Resources Research Center, Kon-Kuk University)
  • 변명희 (건국대학교 축산대학 축산가공학과) ;
  • 최미정 (건국대학교 축산대학 축산가공학과) ;
  • 이성 (한서대학교 식품생물공학과) ;
  • 민상기 (건국대학교 동물자원연구센터)
  • Published : 1998.06.01

Abstract

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, 80$\times$20mm) were frozen unidirectionally (Neumann's model) from the bottom at -45, -30, -20, and -15$^{\circ}C$ 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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