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Evaluation of farming practices on Pseudomonas counts in raw milk (Pseudo-MILQ)
Project
Project code: MRI-MBT-08-1040 Pseudo-MILQ, AiF 20027 N
Contract period: 01.07.2018
- 31.03.2021
Purpose of research: Applied research
Refrigerated storage of raw milk is a prerequisite in the dairy industry. However, psychrotrophic bacteria can proliferate and contribute to spoilage of ultrahigh temperature (UHT) treated and sterilized milk, as well as other dairy products with a long shelf life due to their ability to produce extracellular, heat resistant enzymes such as peptidases and lipases. Especially members of the genus Pseudomonas are reported as the most important milk spoilers. The residual activity of their extracellular enzymes after UHT treatment may lead to technological problems (off flavors, physico-chemical instability) during the shelf life of milk and dairy products. In order to prevent these negative spoilage effects Pseudomonas counts of raw milk must kept low. Apart from the prolonged storage of raw milk, other factors that contribute to increased Pseudomonas counts during milk storage and processing remain unknown. It is supposed that primary production on farms significantly influences Pseudomonas counts in raw milk. Our proposed project is focused on the evaluation of those critical points by analyzing different farming practices (systems of milking and husbandry, size of farms, geographical regions) with regard to Pseudomonas counts. Moreover, factors of raw milk storage period and biofilm production of Pseudomonas along with a release of proteases are evaluated. With the upcoming results it should be possible to assess conditions of milk production and husbandry with respect to enzymatic milk quality and to make recommendations for the reduction of Pseudomonas counts in raw milk.
Current interim results of the project are listed below. In cooperation with the research unit TUM and the project-accompanying committee, the logistics and time intervals of the raw milk sample collection as well as the definition and recording of relevant farm parameters were determined. The laboratory work for the extraction of bacterial DNA from raw milk is carried out in a coordinated effort at MRI and TUM research institutions. Furthermore, the Pseudomonas bacterial count was determined with culture-based and molecular methods. Regarding these, bacterial counts on selective agar for Pseudomonas were detectable in approx. 25% of the examined raw milk samples at values of ≥ 104 CFU/ml. The average Pseudomonas load of 418 samples analyzed by qPCR was 105 CFU/ml, with 10 % of the samples showing bacterial counts from 104 CFU/ml up to 108 CFU/ml. The first data on microbial analyses of 420 raw milk samples showed a high bacterial diversity with 40 to 500 genera per sample. The average proportion of Pseudomonas was 2.4%, with about one tenth of the samples showing highly varying values between 5 and 99% Pseudomonas.
The experiments on the biofilm forming capacity of raw milk associated pseudomonads were carried out in differently concentrated milk media at 6°C. The biofilm formation of the Pseudomonas isolates investigated was shown to be highly strain- and species-specific. Pseudomonas protegens proved to be a strong biofilm producer under the conditions of the investigation.
Section overview
Subjects
- Animal Husbandry
- Animal health
- Food Processing
- Food microbiology
Framework programme
Funding programme
Excutive institution
MRI - Department of Microbiology and Biotechnology (MRI-MBT)
