Drying of biological materials

Tray dryers, the simplest type of dryer, are commonly used for batch drying of biological materials, where the wet solids are placed on trays which are then transferred into a chamber. The chamber may have a heating jacket, heated tray supports, or a hot air supply. Vacuum may be applied to reduce the temperature at which the liquid evaporates, preserving heat labile products. These are well suited to low-volume products or flexible plants where a number of different products with different characteristics must be dried. They are relatively inefficient to operate, difficult to clean, and labor intensive to operate. The product is exposed when being loaded and unloaded, so the dryer may need to be located in a clean room or area for pharmaceutical products. 

Rowe, T.W. Freeze drying of biological materials some physical and engineering aspects. In Current Trends in Cryobiology, Smith, A.U., Ed. Plenum Press New York, 1970 60-138. 

Millqvish-Fureby A, Malmsten M, Bergenstahl B. An aqueous polymer two-phase system as carrier in the spray-drying of biological material. J Colloid Interface Sci 225(1)54-61, 2000. 

Adams, G.D.J. (1991). Freeze-Drying of biological materials, Drying Technology, 9(4), 891-925. 

FIGURE 9.11-2. M odel for uniformly retreating ice front in freeze drying. Sec. 9.11 Freeze Drying of Biological Materials... 

Drying of Biological Material in Tray Dryer. A granular biological material wet... 

The obtaining of such reliable results on minute samples makes it possible to discover how the chemical composition of biological materials varies from one small section to another. The data thus obtained can be combined with dry-weight data from absorptiometry with polychromatic beams to yield conclusions of the,kind listed in Table 11-4. 

Thus, in the observation of the drying process of biological materials, the water activity is at least as valuable as the water content of a material. As water activity measurements are complete in about 3 min, they represent a useful tool for control of the drying process. 

Koln, pp. 3-19,1962 MacKenzie, A.P. A current understanding of the freeze-drying of representative aqueous solutions. Fundamentals and applications of freeze-drying to biological materials, drugs and foodstuffs, 1.35... 

According to Stoeppler et al. [15], severe errors up to a factor of two may result from ETA—AAS analysis of biological materials without some form of sample pretreatment. The approaches that will be discussed here are (a) the use of diluent solutions to minimise matrix and molecular absorption interferences (b) partial decomposition techniques in which metals are extracted from proteins with acids (c) dissolution of tissue samples without complete oxidation (d) complete oxidation procedures such as dry ashing, wet digestion at ambient and elevated pressures, and low temperature ashing with reactive gases at low pressures. 

Mader, P., Szakova, J., Curdova, E. Combination of classical dry ashing with stripping voltammetry in trace element analysis of biological materials review of literature published after 1978. Talanta 43, 521-534 (1996)... 

P. P. DeLuca. Fundamentals of freeze-drying pharmaceuticals, in Fundamentals and Applications of Freeze-Drying to Biological Materials, Drugs, and Foodstuffs, International Institute of Refrigeration, Commission Cl, Tokyo, 1985, pp. 79-85. 

The type of raw material is of extreme importance in the drying process for instance, to retain the viability and the activity of biological materials such as blood plasma and fermentation products, the operation is carried out at very low temperatures, while more severe conditions can be applied to foodstuffs. 

The use of activation methods for the analysis of biological material has been reviewed by Bowen ( 7). In Instrumental Neutron Activation Analysis, the dried sample is placed in the core of a nuclear reactor where it is bombarded with neutrons. Many of the elements present in the sample undergo nuclear reactions of which the most common are the (n, y) type. The products of these reactions are radioactive and decay with the emission of gamma photons of characteristic energy. 

The first measurement which we made on the model system, namely, the conductivity, is the most difficult to make on this type of biological material because the lamella of the chloroplasts are very small (30 to 60 A thick). However, there have been conductivity measurements on dried chloroplast preparations which show that they are indeed photo-conductive. Although these are subject to questionable interpretation in such a complex system (39, 40), the photoconductive behavior of a chromatophore film is shown in Fig. 15. 

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