Compression of Foods during Freeze-Drying: Water Plasticization at the Ice-Dry Layer Interface
The compressive mechanical properties of freeze-dried green beans show a pronounced decrease in rigidity when moisture content and/or temperature are increased. There exist several temperature and moisture combinations which give common values for mechanical properties. These combinations also give a common compressive behavior. Using this information on mechanical properties, it is possible to predict a stress-strain relationship, if given either a temperature, a moisture content, or the value of a pertinent mechanical property.
It is shown that the moisture contents and temperatures that exist in the dry layer during freeze-drying result in mechanical properties that are suitable for compression of the dry layer. From studies on compression behavior during freeze-drying, it is shown that applied compressive pressure is the main determinant of final degree of compression. Increasing the compressive pressure gave a higher compression effect and gave a more rapid drying, presumably due to improved heat transfer in the compressed dry layer.
From the above information, a simple method to predict compression behavior during freeze-drying was developed.
KeywordsCompressive Pressure Compression Behavior Tangent Modulus Green Bean Instron Test Machine
Unable to display preview. Download preview PDF.
- 1.S-H. Emami, Mechanical compression of food products during freezedrying through force produced by springs, M.Sc. Thesis, MIT, Cambridge, MA (1976).Google Scholar
- 2.G. Beke, The effect of sublimation temperature on the rate of freeze-drying process and upon the volumetric change in meat muscle tissue, in: “Proceedings XII International Congress Refrigeration,” Vol. 3, Madrid (1969).Google Scholar
- 3.J.D. Hatcher, The use of gamma radiation to measure moisture distribution during drying processes, M.S. Thesis, Georgia Institute of Technology (1964).Google Scholar
- 5.A. Margaritis and C.J. King, Factors governing the terminal rates of freeze-drying of poultry meat, Chem. Eng. Prog. Symp. Ser. No. 108 67:112 (1971).Google Scholar
- 7.A.M. Brajnikov, A.I. Vassiliev, V.A. Voskoboinikov, and E.I. Kantchechivili, Transfer de chaleur et de masse dans les materiaux poreaux pendant le lyophilisation sous vide, Bull. Int. Inst. Refrig. Annex 1969 4:11 (1969).Google Scholar
- 8.S.H. Emami, Compression of foods during vacuum freeze dehydration, Ph.D. Thesis, Massachusetts Institute of Technology (1979).Google Scholar
- 9.M. Karel, Freeze-dehydration of foods, in: “Principles of Food Science, Part II, Physical Principles of Food Preservation,” O.R. Fennema, ed., Vol. 4, Marcel Dekker, New York (1975).Google Scholar
- 11.C.J. King, “Freeze Drying of Foods,” CRC Press, Cleveland (1971).Google Scholar
- 13.G.L. Gentzler and F.W. Schmidt, Thermodynamic properties of various water phases relative to freeze drying, Trans. ASAE 16:179 (1973).Google Scholar
- 14.G.W. Oetjen, Continuous freeze drying of granulates with drying times in the 5–10 minutes range, in: “Proceedings of XII International Congress of Refrigeration,” Vol. 3, AVI, Washington, DC (1973).Google Scholar
- 16.A.P. MacKenzie and B.J. Luyet, Recovery of compressed dehydrated foods, Phase II., Technical Report 72-33-FL, U.S. Army Natick Laboratories, Natick, MA (1971).Google Scholar
- 18.C. Emami and J.M. Flink, Continual hydraulic compression of food during freeze drying, submitted for publication.Google Scholar