From modeling to commercialization: Improving the freeze-drying process
The process of lyophilization, or freeze-drying, is used widely in the food and pharmaceutical industries to preserve biological molecules as well as whole cells. Unfortunately, many freeze-dried products, such as bacterial cultures used in the production of yogurt or cheese, typically lose much of their activity after a few weeks of storage at room temperature. Professor Juan de Pablo's research group has used both theory and experiment to develop a better method, on which they have a patent pending, to stabilize biological substances during lyophilization. Working with researchers from Rhodia Inc., a Madison-based producer of probiotics, or beneficial bacteria, the process is now nearing commercialization.
Stresses induced during freeze-drying by temperature changes, phase changes and drying tend to damage proteins, cell membranes and other structures. Many compounds, especially the saccharides, have been studied empirically for their cryoprotectant properties. In particular, trehalose, a disaccharide of glucose, has been found to be particularly effective at protecting proteins during freezing and drying, and at preventing damaging changes in cell membranes on cooling. To understand how trehalose functions as a cryoprotectant and to guide their experimental efforts to develop a better freeze-drying process, Juan and his group have developed a molecular model for trehalose and used it to study the thermophysical behavior of its aqueous solutions.
During lyophilization, trehalose helps form glassy solids that coat and protect cells, as well as enzymes and other proteins, against damage from ice formation. Juan's group has improved on this by adding sodium tetraborate decahydrate to the mix. The borate crosslinks the trehalose molecules, forming a protective gel. Citric and lactic acids are used to counteract the high pH resulting from the addition of borate.
The Rhodia collaboration allowed Juan's group to expand their laboratory tests of these materials from enzymes and other proteins to several classes of bacteria as well. Nancy Ekdawi-Sever, a PhD student in Juan's group, has worked with Rhodia scientists to show that the freeze-dried bacterial cultures retain most of their activity even after several months' storage at 40 to 50 degrees Celsius. She has also worked to optimize the formulation for each type of probiotic and improve the freeze-drying protocol to determine how much drying is necessary to yield the best stability. As a result, the process now offers an economically attractive alternative to current industry practice, and Rhodia hopes to adopt the process this year for use with their own freeze-dried probiotics. What is more, according to Juan, "by collaborating with industry, we make sure that the things we do are relevant in practice, which should always be an important goal for an engineer."
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Date last modified: Saturday, 28-Jul-2001 07:17:00 CDT
Date created: 16-Aug-1999