Crude venom extracted from scorpions is an aqueous mixture containing salts, free amino acids and small organic molecules alongside proteins and peptides. The presence of water in this mixture creates two problems: hydrolytic and enzymatic degradation continue, and conditions remain favourable for microbial growth. Lyophilization largely eliminates both problems by removing the water without heating.
The first approach to drying that comes to mind is heating, but this is not suitable for a material containing proteins and peptides. Heat unfolds folded structures and can lead to irreversible aggregation. Freeze-drying, by contrast, keeps the sample at low temperature by converting water directly from the solid phase to vapour. In addition, because the process is completed in the sample's own container, losses during transfer are reduced; when dissolved, the resulting cake largely restores the original composition.
How does the process work?
Freeze-drying is carried out in three stages:
- Freezing: The sample is cooled so that the water it contains turns into ice crystals. Because the freezing rate determines crystal size, it also affects the efficiency of the subsequent drying.
- Primary drying: The pressure is lowered and controlled heat is applied to the shelf. The ice turns directly into vapour without passing through the liquid phase; this phase change is called sublimation. Most of the sample's free water is removed at this stage.
- Secondary drying: Bound water held on molecular surfaces is removed by desorption as the shelf temperature is raised gradually. What remains at the end is a light, porous cake.
The general principles of the method and the equipment side are covered in detail in the article on lyophilization.
Shelf temperature and chamber pressure are monitored throughout all three stages. If the shelf is heated too much during primary drying, the frozen structure collapses and a shrunken residue forms instead of a porous cake; if it is kept too cold, the process takes unnecessarily long. For this reason, the cycle parameters are set according to the material and entered in the batch record.
What the powder form provides
- Chemical stability: When water activity drops, hydrolysis and proteolysis slow down, and drift in the peptide profile over time is limited.
- Microbiological safety: A dry environment does not support the growth of microorganisms.
- Weighability: The powder can be weighed directly on an analytical balance; the laboratory prepares its own dilution with its own buffer.
- Ease of transport: Mass and volume are reduced, and the risk of breakage and leakage is lower.
- Long-term storage: When the powder is kept in a closed container, cold and away from light, its shelf life is markedly longer than that of the liquid form.
All of these advantages depend on a single condition: the powder staying dry. Each time the container is opened, moisture gets in, the powder absorbs it and some of the stability gained is lost. For this reason, the container is opened only once it has reached room temperature; if the lid of a cold container is opened too early, water condensing on the surface goes straight into the sample. Working with small aliquots also avoids opening the main stock again and again.
Comparison of powder and liquid forms
| Property | Lyophilized powder | Liquid |
|---|---|---|
| Appearance | White powder | Clear liquid |
| Solubility | Soluble | Soluble |
| pH (20 °C) | Not stated separately in the product specification | 3,5 |
| Odour | Characteristic | Characteristic |
| Weighing | Directly by mass | By volume and concentration |
| Transport load | Low mass and volume | Liquid volume and the need for a leak-proof seal |
The pH row in the table needs attention. The value of 3.5 given for the liquid product form is the product's own specification. The pH 5.72 in the analysis report for the reference batch, however, is the result of a measurement made on the sample delivered to the laboratory as powder. The two figures belong to different contexts and should not be compared directly. Batch-specific measurement values are published on the analysis page.
Post-drying checks
Once drying is complete, the sample is not yet considered ready for shipment. First comes a visual check: are the colour, distribution and texture of the cake as expected? Solubility is then tested: if the powder gives a clear solution within the expected time, the structure has been largely preserved. Measurements such as protein concentration and pH are made on the sample and entered in the batch documentation. At the packaging step, the container is sealed so as to protect it from moisture and light; the label shows the species, the batch information and the use restriction. When these checks are recorded, any later question about the sample can be traced back to the conditions under which the batch was dried.
Limits of lyophilization
Freeze-drying does not solve every problem. The mechanical and osmotic stress that arises during freezing and drying can cause irreversible changes in some protein structures; for this reason, the freezing rate, shelf temperature and vacuum profile are recorded throughout the process. The resulting cake is hygroscopic: when the container is opened, it quickly draws in ambient moisture, and powder that has taken up moisture again does not show the stability of a sample kept dry. Repeated freeze-thaw cycles also wear down the profile; for this reason, working with aliquots divided according to the amount used is preferred over a single large stock. Storage conditions are discussed in detail in the articles on the cold chain and venom stability.
The liquid form is not without its advantages. A sample received as a solution requires no extra dissolution step in the laboratory and carries no risk of weighing error. On the other hand, it is highly sensitive to temperature fluctuations; the longer the shipping time, the more critical it becomes that the cold chain is maintained without interruption. The choice is often made on the basis of how long the sample will be stored and how far it has to travel.
The technical specifications and packaging options for both forms are available on the products page. The products are for research and industrial use only.
