Storage residual moisture content

The storage of a freeze dried product starts with the end of the secondary drying and its transfer into a suitable packing. In the drying plant a certain residual moisture content (RM) is achieved as a function of the product temperature and the drying time (Section 1.2.2). 

Merika [3.51] emphasized from his 17 years of experience with the quality control of freeze dried transplants the importance of sterility and residual moisture control as the decisive characteristics. Furthermore, the leak tightness of the storage containers was constantly controlled. Merika did not measure the product temperature during drying, but controled the process by measuring water vapor pressure and temperatures of the shelves and the condenser. The residual moisture content after 2 years of storage must be below 5 %. All products were sterilized by gamma radiation. 

Kapsalis et al. [4.12] showed, that the residual moisture content RM of peas should neither be to small nor too high. During 84 days-storage at +43 °C and RM below 5 %, the thiamine content was barely reduced, but the carotene content fell to approx. 36 %. On the other hand, the thiamine content fell at RM 33 % to 81 %, while 50 % of the carotene content was preserved. These and other reasons not discussed here led Kapsalis to the conclusion, that an optimum RM does generally not exist, but only a desirable RM for one type of product under given storage conditions. 

Fig. 4.5. Peroxide and free fatty acids data as a function the residual moisture content after storage of the dried product for 10 days at +37 °C.

The freezing of a product is a very important step. The structure in the frozen product decides whether the product can be freeze-dried at all and under which conditions it can be done. For this reason, the consequences of the freezing rate, layer thickness of the product and excipients are discussed in some detail. The second main point is the measurement and control of the two drying phases the main and secondary drying and the third concentrates on the residual moisture content, its measurement and the consequences during storage of the dry product. There will be critical opinions that some of the processes are unilaterally represented. aim was to show the, hmrts and the advantages ot certain procedures to enable the reader to decide whether the ideas of the quoted authors, or my own can be applied to his tasks. 

During the storage of a freeze-dried product, its qualities can change under the influence of at least three conditions residual moisture content, storage temperature and gas mix in the packing, assuming that the freeze-drying itself has been carried out under optimum conditions and the product had the intended qualities at the end... 

T. Nei, H. Souzu, and T. Araki, Effect of residual moisture content on the survival of freeze-dried bacteria during storage under various conditions. Cryobiology 2.-276-279 (1966). 

The residual moisture content in the dried material at the end of the secondary drying stage, as well as the temperature at which the dried material is kept in storage, are... 

As a rule, in conjunction with grinding, the coal is dried to a residual moisture content of between 0.5 and 1.5%, which is suitable for firing. Completely dry coal is more difficult to ignite. In systems with intermediate storage of the pulverized coal it is, however, preferable to reduce the moisture content to below 1 % in order avoid possible trouble with build-up (caking) and difficulties at bin discharge outlets, rotary gates and screw conveyors. 

Excessive or insufficient acid development during manufacture can produce variability in the moisture content of cheese and defects in flavor, body, texture, color, and finish (Van Slyke and Price 1952). The rate of lactose fermentation varies with the type of cheese, but the conversion to lactic acid is virtually complete during the first weeks of aging (Van Slyke and Price 1952 Turner and Thomas 1980). Very small amounts of lactose and galactose may be found in cheese months after manufacture. (Huffman and Kristoffersen 1984 Turner and Thomas 1980 Harvey et al. 1981 Thomas and Pearce 1981). Turner and Thomas (1980) showed that the fermentation of residual lactose in Cheddar cheese is affected by the storage temperature, the salt level in the cheese and the salt tolerance of the starter used. 

Once the soil has been sieved, as much plant and animal residues must be removed as possible. This is best done with a pair of forceps, one small portion of soil at a time. The bulk soil should be covered to prevent any further drying. When the soil has been picked over, subsamples can be taken for determination of moisture content and water-holding capacity (WHC see following section) the soil should be stored at 4°C until use. It is advisable to use the soil as quickly as possible, and if storage is unavoidable, it should not normally exceed 3 months. 

More recently, pyrraline was found to increase almost linearly with time during the storage of freeze-dried milk at 70 °C. The amount formed increased with moisture content, reaching more than 5000 mg kg 1 protein in 50 h with 9% moisture.354 Values of up to 3100 mg kg 1 protein were found in some samples of milk or whey powder. Remarkably high amounts (200-3700 mg kg 1 protein) were also found in bakery products, indicating that up to 15% of the lysine residues may have been modified. 

Figure 10 The stability of a freeze-dried monoclonal antibody/vinca alkaloid conjugate formulation. Desacetylvinblastine hydrazide is linked to the KSl/4 monoclonal antibody via aldehyde residues of the oxidized carbohydrate groups on the antibody. The formulation is conjugate/glycine/mannitol in a I I I weight ratio. Storage temperatures are 25°C and 40°C for samples with moisture contents of 1.4%, 3.0%, and 4.7%. ( ) Dimer formation. (A) Free vinca generation (hydrolysis). ( ) Vinca degradation. (—) Best fit to the WLF equation. (Reproduced with permission from [54].)...

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