Microbiological Quality of Raw Donkey Milk from Serbia and Its Antibacterial Properties at Pre-Cooling Temperature.

Simple Summary: The purpose of this study was to investigate the microbiological quality of raw Domestic Balkan donkey milk and to determine changes in its microbiota during six-day storage at 4 °C, and to investigate the antibacterial activity of this milk toward some foodborne pathogens at a selected pre-cooling temperature of the milk (15 °C). Lysozyme and lactoferrin content in donkey milk were also determined. Absence of pathogens and low levels of total bacterial count, lactic acid bacteria and coagulase-positive staphylococci in 137 samples tested indicated good hygiene practice during milking. Regarding the antimicrobial potential of donkey milk, E. coli appeared to be the most sensitive to the antibacterial potential of donkey milk while S. aureus was the most resistant to the antibacterial effect of this milk. The microbial quality of donkey milk during prolonged storage also indicated the antibacterial activity of this milk. Lysozyme and lactoferrin were present at concentrations of 2.63 ± 0.03 g L−1 and 15.48 mg L−1, respectively. The aim of this study was to examine the microbiological quality of raw donkey milk of an indigenous Serbian breed as well as the changes in the microbial populations during storage at 4 °C. In addition, antibacterial activity of donkey milk against E. coli, L. monocytogenes and S. aureus at 15 °C as well as the content of the two main antibacterial proteins lysozyme and lactoferrin were investigated. Microbiological examination of 137 individual milk samples collected over a period of 21 months showed good microbiological quality since foodborne pathogens such as Salmonella spp. and L. monocytogenes were not detected in any of the analyzed samples, while the number of E. coli, Enterobacteriaceae, total coliform bacteria, sulfite-reducing Clostridia and aerobic sporogenic bacteria was below the limit of quantification (<1 cfu mL−1). During the six-days storage at 4 °C, total bacterial counts and the counts of lactic acid bacteria remained at the initial level while pathogenic bacteria were not detected. The strongest antibacterial activity of the tested milk was observed against E. coli, while S. aureus was the least sensitive to milk antibacterial compounds. Although further research is needed to fully elucidate the antibacterial mechanism and synergistic activity of different compounds in donkey milk, the high content lysozyme (2.63 ± 0.03 g L−1) and lactoferrin (15.48 mg L−1) observed in tested milk could contribute to its strong antibacterial activity and extension of the storage period during which it can be safely consumed. [ABSTRACT FROM AUTHOR]