Metaproteomic analysis of microbial cells during cold storage of raw milk

Abstract:

Raw milk usually needs to be refrigerated at 4 ℃ before being put into production. In this process, microbial contamination will cause deterioration of the refrigerated milk.[Objective] To investigate the dynamic changes of differential proteins expressed by microorganisms during raw milk refrigeration and thereby to lay a theoretical foundation for raw milk refrigeration [Methods] Label-free technology was used to study the species origins and functions of microbial proteins during the 6-day cold storage of raw milk at 4 ℃ and the pathways involved, screen differential proteins, and explore the pathways of the main differential proteins to explore their changing laws.[Results] A total of 341 microbial proteins were identified during refrigeration, of which 60.12% were detected after 3 days of freezing. The analysis of the cluster of orthologous groups (COG) of proteins and kyoto encyclopedia of genes and genomes (KEGG) suggested that the functions of the proteins and the pathways involved changed with time. The number of proteins involved in glycolysis/gluconeogenesis, ATP-binding cassette (ABC) transporter, amino sugar and nucleotide sugar metabolism increased significantly after 4 days of cold storage. The number of differential proteins at adjacent time points gradually increased over time, and different pathways were enriched for them. [Conclusion] The pathways involved in the proteins produced by microorganisms in raw milk during refrigeration and the functions are complex, with the most obvious changes on the 4th day, which may be a key time point for quality control of raw milk.