Freeze-drying definition

Since the definition of the glass phase is fuzzy as Reid et al. [1.17] note, and the methods of measurement can be chosen, the results for Tg- will have a range of variations. For freeze drying one can summarize ... 

According to the operational definition, it is most important that well-defined methods and clear protocols are provided describing the isolation procedure applied. After isolation, freeze-drying is often used to stabilize the final fraction and to prevent chemical and biological reactions during storage. Critical reviews on the isolation and concentration techniques for aquatic substances are given by Aiken (1985), Leenheer (1985), and Abbt-Braun and Frimmel (2002). 

At first sight, then, complex mechanical setups as we propose for semicon-tinuous or continuous freeze-drying seem susceptible to serious hazards in the sterility control of the operation. However, this is not as dramatic as it looks since the essential part of the process—if not the entire process—is carried out automatically and can be done entirely within a sterile environment by remote control. Indeed, today highly sophisticated automation can be achieved if we resort to the advanced technologies developed for the nuclear industry and profit by the experience of their operators. However, this sophistication will definitely bear on the cost and this can be a serious drawback for conventional low-priced products. 

Water activity has been shown to have a definite influence on the rate of degradation of chlorophyll in freeze-dried, blanched spinach puree [73]. At 37°C and an higher than 0.32, the most important mechanism of chlorophyll degradation was conversion to pheophytin. At lower than 0.32, the rate of pheophytin formation in spinach was low. The rate of chlorophyll-a transformation was 2.5 times faster than chlorophyll-. The study of the degradation of chlorophyll as a function of a . pH, and temperature in a spinach system... 

This chapter does not deal with the electronic soft- and hardware to document the data, to calculate the desired results, and to monitor failures. The hardware is available in different configurations and the software can be bought or developed to fit into the software used in production. The prerequisites discussed are those for the methods of measurements and the plant layout to permit automation. The general prerequisite is the use of the same freeze-drying methods from product development through pilot plant studies to production for example, the same principle of temperature and pressure measurements, identical definitions of tolerances, and similar criteria for statistical evaluations. If this prerequisite is not observed, the development steps may have to be repeated to permit later automation. 

The separation operation of drying converts a solid, semisolid, or liquid feedstock into a solid product by evaporation of the liquid into a vapor phase through application of heat. In the special case of freeze drying, which takes place below the triple point of the liquid that is removed, drying occurs by sublimation of the solid phase directly into the vapor phase. This definition thus excludes conversion of a liquid phase into a concentrated liquid phase... 

An outbreak of jaundice associated with the use of a commercial brand of freeze-dried factor VIII concentrate has been reported from a haemophilia centre. The product was administered to 18 patients, 2 of whom developed hepatitis B and S others a non-B type hepatitis, whilst 2 patients contracted both types of hepatitis in succession. Freeze-dried factor VIII concentrate has quite definite advantages over cryoprecipi-tate, but the risk of hepatitis is considerable if a commercial concentrate prepared from large pools of plasma from paid donors is used (15 ). 

Many aromatic hydrocarbons, for example, benzene, ethylbenzene, toluene, cymene and tetrahydronaphthalene, yield additive compounds.5 Such are also formed with liquid cyclic hydrocarbons in the absence of moisture and phenols, and use has been made of this fact to remove sulphur dioxide from a dry gas containing it.6 Additive compounds are also formed with methyl alcohol, thus CH30H.S02 and 2CH30H.S02, the existence of which has been demonstrated definitely by means of the freezing-point curve.7 The additive compound with camphor has already been mentioned (p. 109). 

Figure 9 shows a load-change cycle which is typical for discontinuous SCF extraction. When the pressure release phase following completion of the extraction is considered, the question arises as to the true temperature course. It is wellknown that the pressure-dependent equilibrium temperature of CO2 falls to -79 C under atmospheric conditions. This relationship leads to short-term thermal stresses within the inner surfaces of the pressure vessel, particularly in the lower part where dry ice may form. There is an additional risk to the process that the charge may freeze within the pressure vessel. When designing equipment for the extraction of natural substances, definition of the non-stationary courses of pressure and temperature during pressure release is therefore of especial importance in the choice of materials and for the geometry of the pressure vessel. 

If the sponge is left to dry in the sun, this adsorbed water will evaporate, leaving only a small proportion of water bound chemically to the salts and to the cellulose of the sponge fibers. Like water in sponge, water is held in food by various physical and chemical mechanisms (Table 3.1). It is a convenient oversimplification to distinguish between free and bound water. The definition of bound water in such a classification poses problems. Fennema (1985) reports seven different definitions of bound water. Some of these definitions are based on the freezability of the bound component, and others rely on its availability as a solvent. He prefers a definition in which bound water is that which exists in the vicinity of solutes and other non-aqueous constituents, exhibits reduced molecular activity and other significantly altered properties as compared with bulk water in the same system, and does not freeze at -40"C."... 

Snap freezing - widely used term to describe freezing tissue for immunocytochemistry the term comes from food preparation industry and for biomedical sciences it has no single definition and can mean freezing in liquid nitrogen, on dry ice, or in isopentane. 

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