So far, probiotic bacteria are mostly freeze-dried, before they are used in high concentrations in foods. However, the freeze-drying process is problematic – for some probiotics it means certain death, and it is also quite energy consuming. The probiotics must first be frozen and in a second step heat is inserted in the sample to transform the ice directly into steam.
The TUM researchers from the Chair of Food Process Engineering and Dairy Technology decided to save themselves this “detour” and tried to find a drying process that is both gentler and more environmentally friendly.
That is how the TUM researchers came across low temperature vacuum drying (LTVD) – a process that runs under mild conditions. The product remains in a liquid state, since in a vacuum the evaporation takes place at low temperatures: For instance, water boils at eight degree centigrade in an atmosphere of ten mbar air pressure. Compared to freeze-drying, this method requires 40 percent less energy.
Low Temperature Vacuum Drying resulted partially in a higher survival rate than conventional drying. For instance, the yoghurt strain Lactobacillus bulgaricus, which barely survives freeze-drying, showed a ten times higher yield following LTVD. The new process will allow health-fostering probiotic “candidates” that are too fragile for conventional manufacturing processes to be used in the food industry. Conversely, it turned out that probiotics that handle freeze-drying very well, performed poorly in low temperature vacuum drying. To cut a long story short: The optimal drying process depends on the respective bacterial strain.
The low temperature vacuum drying process is not only the most energy efficient one; it also has a positive influence on storage stability. Compared to probiotics from conventional freeze-drying, probiotics in powder form produced using LTVD keep significantly longer in mueslis or infant formula once the packaging is opened.
MEDICA.de; Source: TU München