Pseudomonas spp. in raw milk

Towards finding new solutions for improving milk quality

The export of German milk products has continuously increased in the last few years. This has resulted in a need for a considerable increase in the shelf life of the exported products to compensate for long transport periods and to satisfy consumer demands for high quality products. This in turn implies special challenges for preserved milk products such as UHT milk, because these can experience sensory and texture defects due to enzymatic protein breakdown before the expiry of the ‘best-before’ date. Protein breakdown is a large extent due to production of proteases by Pseudomonas bacteria. Pseudomonads are cold-tolerant and can grow under cold-storage conditions and produce peptidases. Based on their high thermostability, once these enzymes are present in the milk, there is no possibility for their elimination. Therefore, it is necessary that the formation of such enzymes during raw milk storage and transport is avoided, which is only feasible by attempting to decrease the numbers of contaminating Pseudomonas in milk. It is currently unknown which factors apart from milk production and storage lead to increases in Pseudomonas levels, but primary contamination at production appears to have a significant influence. Nevertheless, it remains unclear where the critical entry points are situated.

These questions are addressed within the framework of a cooperative project between the Department of Microbiology and Biotechnology of the Max Rubner-Institut and the Technical University of Munich that is funded by the Research Circle Nutrition Industry (Forschungskreis Ernährungsindustrie FEI, AiF 20027). The project investigates the effect of farm-specific factors affecting Pseudomonas contamination and the reduction of pseudomonas counts and a resulting decrease of proteolytic enzymes in raw milk, taking different operational structures and production at different regions of Germany into consideration. A research focus will be placed on the relationship between specific milk production factors and the raw milk microbiome, and especially with increased Pseudomonas counts.  However, specific contributing factors such as the influence of the storage time, transport of raw milk into the dairy, as well as the capacities of Pseudomonas strains for producing biofilms and peptidases will be investigated.

By analyzing the farm-specific factors it will be possible for the first time to assess milk production and storage conditions in view of their impact on enzymatic quality of the milk and to deduce specific recommendations for the reduction of unwanted Pseudomonas contamination. This will enable both milk producers and dairies to minimize enzyme production as a key factor for a successful quality assurance.