Effects of the Cold Atmospheric Plasma Treatment Technology on Staphylococcus Aureus and Escherichia Coli Populations in Raw Milk

Abstract

Today, various sterilization methods are used for the removal of microorganisms, some of which are based on thermal methods that have negative effects on the physicochemical properties of milk. The present study aimed to investigate the effects of cold plasma at atmospheric pressure on the population of Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) in raw milk. Initially, a plasma jet filled with argon gas was used to evaluate the antibacterial effects of cold plasma. Following that, pasteurized milk samples (1.5% and 3% fat) were infected with standard strains of E. coli and coagulase-positive S. aureus and irradiated with cold plasma at the frequency of 22, 28, and 33 kHz and voltage of 20, 12.5, and 10 kV for five minutes. The results of statistical analysis and Tukey’s test indicated that the E. coli and S. aureus microbial load was significantly lower in the 1.5% fat milk compared to the control group (P<0.05). In addition, the milk samples exposed to plasma at 20 kV and 28 kHz showed the most significant reduction in the number of E. coli bacteria compared to the control samples (P<0.05). The milk samples exposed to 10 kV and 33 kHz also showed the most significant reduction in the S. aureus microbial load. According to the results, cold plasma could decrease the microbial load of milk containing 1.5% fat more significantly compared to the 3% fat milk. Therefore, plasma could be a proper alternative to thermal decontamination methods for raw milk. However, its application requires further studies to determine the intensity and duration of the exposure of microorganisms to cold plasma at atmospheric pressure.

Keywords

• cold plasma
• milk
• microbial load reduction
• sterilization
• microbial inactivation