Effect of ozonation on the Staphylococcus Aureus innoculated in milk

Abstract

The aim of this research was evaluate the efficiency of the action of ozonation of milk on the reduction of the bacterial counts of Staphylococcus aureus artificially inoculated and subjected to different binomials times/concentrations of ozone. The samples were divided in four assays: 1 and 2, with skim milk and ozone concentrations of 34.7 mg L –1 and 44.8 mg L-1, respectively, and assays 3 and 4, with whole milk and the same concentrations of ozone. The time of ozonation in all of the assays was 5 (T1), 10 (T2), 15 (T3), 20 (T4) and 25 (T5) minutes. Each treatment was replicated three times. The bacterial counts were determined immediately before and after the ozonation process by plating the samples on Baird Parker agar. In treatments 1 and 2, the greatest reductions were 0.42 log10 CFU/mL (colony forming units per millilitre), whereas in treatments 3 and 4, the greatest reductions were 0.19 and 0.21 log10 CFU/mL, respectively. The results of all of the tests show that, for T1, there was no reduction in the microbial load, whereas for T2, there was a sharp decrease in the microbiota, and this decrease was even more significant for T4 and T5. In both skim and whole milk with ozone concentrations of 34.7 and 44.8 mg L-1, the reductions were significantly greater after 20 minutes of ozonation. The results indicated that ozone showed low efficacy in the reduction of S.aureus inoculated into fluid milk and milk fat interferes with the bactericidal action of the gas.