Beyond Freeze-Drying

Food scientists have gone far beyond freeze-dried ice cream when it comes to creating high-tech food for astronauts. Salt and pepper are turned into liquids so that they do not float around in zero gravity, and perishable fruits and meat can be thermostabiUzed (processed with heat) to allow them to stay fresh for long space journeys. 

According to Labuza et al. [18], water binds (via hydrogen bonds) to the hydroperoxides generated upon oxidation reactions at the surface of the freeze-dried product. This hydration prevents the decomposition of the hydroperoxides and therefore slows down the oxidation. For low levels of residual moisture, few water molecules are able to bind to the hydroperoxides the oxidation rate is great. The increase in residual moisture induces a better protection and thus a decrease in oxidation. Beyond a specific level of residual moisture, oxidation increases... 

Beyond 0°C, ice melts and another phenomenon, evaporation, takes place. Melting during the freeze-drying process may destroy the product and should be avoided (back melting). 

Setting the product composition of a pharmaceutical preparation, so as to effect an efficient and economical drying cycle, will probably always be beyond the remit of the process engineer. However, bearing in mind the complexities of the freeze-drying process, its optimisation should be given due consideration even by those responsible for product development. 

A fully amorphous (glassy) freeze-dried product, consisting of 5% of a calcitonin gene-related protein (CGRP), 95% lactose and 3% residual water, was heated gently in a sealed DSC capsule. Its Tg is shown by the endothermic step in Scan 1 of Figure 4. Heating beyond Tg makes a material susceptible to more or less rapid physical and/or chemical... 

Click chemistry has proven to be a valuable tool to stabilize self-assembled nucleic acid nanostructures by covalent cross-links that are more stable to denaturing agents, or can, for example, be freeze-dried. Discussing various aspects of nanostructure stabilization will go beyond the scope of this chapter. Thus, only selected examples involving click chemistry for DNA nanostructure assembly and stabilization are presented. 

No new laboratory facilities are required for - H NMR spectroscopy beyond those necessary for the conduct of work with tritiated compounds. Tritiated compounds recovered from tracer and other experiments are usually in very dilute solution and then will need to be concentrated by freeze-drying and redissolution in a small volume of NMR solvent containing internal H reference (i.e., tetramethylsilane or sodium 4,4-dimethyl-4-silapentanesulphonate). This solution, having sufficient total... 

It is beyond the scope of this chapter to indulge in more details about this technique, but it might be of interest to note that it allows the evaluation of the influence, on the product structure, of different factors such as the initial concentration of the starting fluid, the rate of freezing (macro or microcrystalline structures), the pertinence of the drying cycle and of the final conditioning. 

There are two different types of water sprinkler systems, wet-pipe and dry-pipe. The lines leading to the sprinkler heads are full of water in a wet-pipe system so that water will be discharged immediately from an open sprinkler head, while in a dry-pipe system, the lines are full of air under pressure instead of water. This latter type of unit should be used where the temperature is not maintained above freezing at aU times. Both types of systems include a main control valve which is designed not only to supply water to the sprinkler heads but also to provide a mechanism to cause an alarm to sound. The valves also usually provide a visual indication of whether they are open or closed. Except during maintenance, they should be in the open position. There are a number of design features for these valves which are beyond the scope of this document, except to note that some are intended to avoid false alarms due to surges or variations in the water supply pressure to the system. 

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