Proteolysis in UHT milk due to Staphylococcus aureus

Abstract: The aim of this project was to analyse the effect of mastitis pathogen Staphylococcus (S.) aureus on proteolysis in UHT milk. S. aureus is one of the main pathogens that causes mastitis and reduces milk yield and quality which both leads to large economical losses. UHT milk was inoculated with four strains of S.aureus and then incubated at 37oC. Milk was sampled at six different time points (0, 0.5, 1, 2, 4, and 6 h). Samples were stored at -200C until analysis for protein separation by capillary electrophoresis (CE). CE was run for two strains (333 and 485) and electropherograms were obtained. Due to the quality of electropherograms only strain 485 was further evaluated for protein quantification. The level of milk proteins (caseins and whey proteins) was estimated for each sample by quantification of peak area. Data were statistically analysed using SAS ANOVA procedures. The lowest pH value of inoculated milk was 6.2, while pH of non-inoculated milk remained constant and was 6.7. Bacterial growth in log phase reached levels of 8x10 8 and 8.7x10 8 colony forming units for strain 333 and 485, respectively. The overall casein content was reduced by up to 21% due to S. aureus.