Dry starter cultures better
TUM researchers are developing environmentally friendly methods to keep probiotics more stable
They are in yoghurts, muesli mixtures and baby milk powder - probiotic bacteria are on the rise as health-promoting additives on the food shelves. However, the production of this "functional food" has its pitfalls: only a few probiotic bacterial strains are so robust that they survive conventional production methods. Process engineers and microbiologists from the Technical University of Munich (TUM) have now jointly developed a particularly gentle process so that previously unused probiotics can also be used in the future. The result helps companies and consumers alike: It saves energy and costs in production and at the same time makes the probiotics last longer.
As functional additives, probiotics promote the immune system and intestinal health. But how do they get into the food packaging? So far, probiotic bacteria have mostly been freeze-dried so that they can then be used in a concentrated form as a food additive. But freeze-drying is problematic - for some probiotics it means certain death from the cold and is also very energy-intensive. Because in the process, the probiotics must first be frozen. In the deep-frozen state, heat is then supplied to them. This converts the ice directly into water vapor, which is extracted from the bacterial preparation. TUM researchers from the Chair of Food Process Engineering and Dairy Technology wanted to shorten this "detour": They therefore went in search of a gentler, more environmentally friendly drying process.
The TUM researchers came across low-temperature vacuum drying (LTVT) because it also works under mild conditions. With this process, however, the product remains liquid: under vacuum, liquid can be evaporated at gentle temperatures - at an air pressure of 10mbar, water boils at around 8°C. Compared to freeze-drying, you can save 40% energy in this way. The team around Dr. Petra Först from the Chair of Food Process Engineering and Dairy Technology investigated this process in an experiment with three probiotic bacterial strains: The TUM researchers first determined the optimal NTVT conditions and then compared the results with classic freeze drying in a second step.
With a surprising result: In some cases, low-temperature vacuum drying led to better survival than conventional freeze-drying. The yoghurt culture Lactobacillus bulgaricus, which barely survives freeze drying, shows a yield that is about ten times better after NTVT. The development of the new process also makes it possible to use probiotic "candidates" with health-promoting properties that are too sensitive for the previous manufacturing process in the food industry. Conversely, it has also been shown that probiotics that survive freeze drying very well perform worse in low-temperature vacuum drying. In short: The most suitable drying process depends on the respective strain of bacteria.
The research team led by Dr. Jürgen Behr from the Chair of Technical Microbiology at TUM. They examined the bacterial strains for possible differences that could explain the unequal behavior in the drying processes: The secret could therefore lie in the bacterial cell membrane, which protects the bacterium from environmental influences. It turned out that this adaptable "protective shield" of the probiotics has a different composition of fatty acids for each bacterial strain. The researchers can now even specifically control this composition by changing the cultivation conditions before the drying process - in a practical test, they were able to increase the survival rate of a bacterial strain by around 50% after drying by optimizing the cultivation conditions.
Incidentally, the low-temperature vacuum drying process not only saves energy, but also has a positive effect on storage stability: probiotics in powder form that were produced using NTVT keep in muesli or baby milk powder much longer after opening the packaging than those from conventional freeze-drying. This means that a higher number of active bacteria remain in the product until it is consumed, even after storage under unfavorable conditions.
Literature:
Foerst, P.; Kulozik, U.; Schmitt, M.; Bauer, S.; Santivarangkna, Ch: Storage stability of vacuum-dried probiotic bacterium Lactobacillus paracasei F19. Food and Bioproducts processing, online pre-publication at http://www.sciencedirect.com/science/article/pii/S096030851100054X (doi: 10.1016/j.fbp.2011.06.004)
Bauer, SAW; Schneider, S.; Behr, J.; Kulozik, U.; Foerst, P.: Combined influence of fermentation and drying conditions on survival and metabolic activity of starter and probiotic cultures after low-temperature vacuum drying. J. Biotechnology, online pre-publication at http://www.sciencedirect.com/science/article/pii/S0168165611003099 (doi: 10.1016/j.jbiotec.2011.06.010)
Source: Munich [TUM]
