Sarah. H. I. Lee, Julia Jacob, Antje Fröhling, Oliver Schlüter and Carlos A. F. Oliveira
University of Sao Paulo, Department of Food Engineering, Av. Duque de Caxias Norte 225, 13635- 900 Pirassununga, SP, Brazil
In this study, the inactivation effect of peracetic acid (PAA, 0.5%) and atmospheric plasma jet (APJ, power: 20 W) on three strains of Staphylococcus aureus and one strain of Listeria monocytogenes were evaluated at different treatment times. PAA treatment was performed directly on liquid phase, with the inoculum suspended in brain-heart-infusion (BHI) broth. APJ assays were conducted on platelets made of polysaccharide gel with 1% calcium chloride. Each platelet was inoculated with 10 μl of each bacterial BHI suspension. For all experiments, the initial concentration was set at 109 CFU/mL, and treatment times were 5, 10, 15, 30, 60 and 120 sec. Results were obtained using flow cytometry and plate count methods. For PAA treatment, inactivation was observed at 120 s for all strains tested, with a decrease of >7 log cycles. However, no inactivation was observed after 120 s of APJ treatment, although the colony counts decreased up to 2 log cycles. Results indicate that APJ had lower efficiency than PAA for inactivation of S. aureus and L. monocytogenes in all treatment times. Further studies with APJ using longer treatment times are necessary to fully describe the kinetics of this technology for inactivation of important food pathogens.
Funding: Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES, PDSE Grant # 99999.004419/2014- 06)
Keywords: S. aureus, L. monocytogenes, cold plasma, sanitizers, inactivation.