Self-Preservation: The lyophilization process and the importance of preservation

Hello, and welcome to the “Colorful Researchers” blog. I’m Bruno, one of the lyophilization specialists at BUCHI. My interest in freeze-drying developed long before I fully understood the process. As an Argentinian, I have always had a passion for the outdoors, and we Argentinians are blessed when it comes to outdoor activities. People from all over the world travel to my country to experience what nature has to offer, and no place is more popular than the Andes. Within the Andes, the most famous peak is Aconcagua, which is not only the highest mountain in Argentina but also the highest peak in the Southern and Western Hemispheres.

It rises to 6,961 meters above sea level and presents a huge challenge for climbers. When researching and training for the challenge of rising to the summit, my friends and I realized we needed to keep the weight of our supplies to a minimum. We also needed high-energy and easy-to-prepare food. The solution came in freeze-dried foods. I remember our first experience trying out this strange ‘space food’ and my reaction when I first learned about the strange process by which this food was produced. I’ll never forget the moment of summiting Aconcagua, and now that I work with freeze-drying technology, I often think about the amazing things achieved due to the lyophilization process.

We needed high-energy and easy-to-prepare food. The solution came in freeze-dried foods

Just as freeze-dried ice cream is strange, so is the process by which it is made. Sublimation turns a solid into a gas without passing through the liquid stage. The lyophilization process involves three key steps:

• Freezing: The product is cooled below its triple point, the lowest temperature at which the material's solid and liquid phases coexist.
• Primary Drying (Sublimation): Heat is applied to the product under reduced pressure, causing the ice to sublimate. This removes most of the water from the product.
• Secondary Drying (Desorption): The product may still contain bound water molecules after sublimation therefore, further drying at elevated temperatures under vacuum removes this bound water.

After the freeze-drying process comes quality control steps to ensure the product meets standards and conforms to applicable regulations. Finally, the dried product is sealed in a moisture- and oxygen-proof packaging (which can be tricky to open with frozen fingers!) to prevent rehydration and oxidation.

Lyophilization is not just used for food. It is also used by pharmaceutical and biotechnology companies to extend and improve the stability of products. There are also several advanced use cases, such as its use in developing electrodes for lithium-ion batteries. 

For this blog, I would like to focus on using the lyophilization process to produce freeze-dried human breast milk, as my colleague Tuan Anh Pham recently hosted a webinar on the topic, which you can check out here. Although preserving the nutrients within the foods my friends and I used when summiting Aconcagua was important, retaining nutrients and bioactive components in breast milk is critical. Breast milk contains essential nutrients such as proteins, carbohydrates (lactose), fats, vitamins, and minerals, which are crucial for infant development. It also contains bioactive components like enzymes, hormones, and growth factors. Everyone knows how quickly milk can go rancid; therefore, freeze-drying is the ideal way to preserve these nutrients and bioactive compounds, which might otherwise be degraded or destroyed.

Breast milk contains essential nutrients, and freeze-drying is the ideal way to preserve these bioactive compounds, which might otherwise be degraded or destroyed

There are many reasons to freeze-dry breast milk. Freeze-drying significantly extends shelf life, which is particularly beneficial for mothers who produce excess milk and want to store it for future use. Like the food climbers use, dried milk is lighter, takes up much less space, and is particularly useful for those with limited or no freezer space. Freeze-dried milk is far easier to carry and doesn’t require thawing out. Additionally, frozen milk lasts for only 3-6 months. In contrast, freeze-dried milk in a three-year accelerated study had no microbial growth, and the nutrients were preserved and largely the same as frozen milk. 

Another issue with stored milk is the bad taste that develops due to lipase activity, and this can be mitigated with optimal freeze-drying conditions. The lyophilization process can vary greatly depending on the product being dried. Pre-treatment steps may be required, and research must be performed to determine the optimal drying conditions. For milk, it is vital to deactivate lipase by making the enzyme inactive. However, it is crucial to get the conditions right, as excessive heat can degrade important nutrients and antibodies. The freezing step is important as rapid freezing helps form smaller ice crystals, which are less disruptive to the milk’s structure. During the drying phases, controlling the temperature and vacuum levels ensures that ice is sublimated without melting. This requires precise equipment and monitoring.

Another issue with stored milk is the bad taste that develops due to lipase activity, and this can be mitigated with optimal freeze-drying conditions

Once the process has been perfected, it is possible to preserve the protective components in milk that have anti-infective actions, such as immunoglobulins, enzymes (lysozyme, lactoferrin., etc.), and cytokines. There are also components that provide passive immunity and stimulate the development of the infant’s immune system, such as nucleotides, lipids, leukocytes, oligosaccharides, and hormones. Freeze drying helps maintain the structural integrity of these components, which is especially important for complex molecules like proteins, which can denature or lose functionality when exposed to heat or harsh drying processes. For more information about the specifics of the freeze-drying process for human breastmilk, I recommend you check out our webinar, where particular challenges are discussed. 

Bueno Chao,
Bruno