Milk – popular and ubiquitous – but quick to spoil and become undrinkable because of the activity of the abundant microorganisms it contains. Pasteurisation, the process of heating milk (and various other foods) to kill pathogenic bacteria, is one of the oldest food preservation methods still in use today.
Microbiology has come a long way since the pioneering work of Louis Pasteur and advances in microbiology allow food scientists new insights into the microbial ecology of milk for the purpose of enhancing milk hygiene and longevity. Naturally-occurring populations of microorganisms, and those remaining intact after pasteurisation can be referred to as the microbiome. The application of molecular biological techniques to the milk microbiome has been shedding light on how to improve the processing of milk.
A recently published study set out to determine more effective milk processing measured by less spoilage, reduced waste and longer lasting milk. Specifically, what was the influence of storage and transportation conditions on the milk that may be adjusted?
The study observed the production and processing of bovine milk over extended period of time in order to capture seasonal variation in the microbiome. The application of microbial gene sequencing and comparative sequence analysis revealed, as is usually the case in microbial ecology, high than previously observed diversity in population structure in raw milk.
Additionally, the structure of the microbiome was observed to change in unpasteurised milk according to the time of year. For instance, milk produced in the spring contained the most genetically diverse microbiome and the highest counts of bacteria with Actinobacteria the dominant type of bacterium. Twenty nine taxonomic groups including Streptococcus, Staphylococcus and Clostridiales composed an ever present core population in raw milk, regardless of the time of year.
Data were generated from milk in transport containers and after transfer to storage silos. A comparison of the microbiomes of transport containers (tanker trucks) and the individual storage silos filled by the trucks revealed an unexpected picture. Most, but not all, microbiomes of stored milk was noticeably different to those microbiomes of the transported milk.
Clearly, the microbiome of the transported milk was of limited influence on the subsequent microbiome of the stored milk. For example, high levels of Streptococcus spp. typically seen in tanker milk usually decreased in silo stored milk. The typical microbiomes of silo stored milk was dominated by Acinetobacter. The researchers suggested that changes in microbiome structure revealed by microbial genetic analysis were due to the milk processing environment.
This and other studies may allow the dairy industry to modify antimicrobial measures during the processing and storage of milk. We have yet another example of how precise, highly detailed empirical information is describing a microbiome and, in so doing, is opening the potential for targeted hygienic intervention rather than broad brush, non-specific approaches. Targeted antimicrobial intervention in the dairy and industries may reduce production costs and use of chemicals and increase shelf life of food products.