Comparative Analysis of the Microbiome in Raw and Pasteurized Bovine Milk From Norway

Background: Bovine milk contains a complex microbial community that influences the product's quality and safety. As a result, a detailed study of this microbiota is critical for the dairy sector. This study aims to investigate the impact of pasteurization on the microbiota of bovine milk from Norway, with a specific focus on characterizing the microbial diversity and identifying potential differences between raw and pasteurized milk. Method: The bacterial composition of raw and pasteurized samples was examined over 11 months (January to November year 2015) at 4 °C using a 16S rRNA amplicon profiling approach. 16S amplicons sequence data from extracted DNA of raw and pasteurized milk samples are publicly available from the European Nucleotide Archive under accession number PRJEB23297. The demultiplexed sequences were processed using the open-source DADA2 R software package. Results: Bacillus was predominant in both raw (58%) and pasteurized (39%) milk samples, with Pseudomonas (10%) and Acinetobacter (9%) prevalent only in raw milk. In pasteurized milk, Streptococcus (11%) and Acinetobacter (11%) follow in abundance. Alpha diversity analysis verified species richness in both raw and pasteurized milk, with some samples displaying distinct microbial communities exhibiting higher or lower richness compared to the median. Beta diversity assessed through Non metric multidimensional scaling (NMDS) and PCA illustrates dissimilarity between raw and pasteurized samples. Conclusion: The findings indicate that pasteurization is effective in reducing the bacterial load in milk samples, but complete elimination is not achieved. Further research is necessary to comprehensively comprehend the significance of these observations and to uncover the underlying factors influencing variations in microbial communities over time.