Inactivation of Staphylococcus aureus and Escherichia coli O157:H7 on fresh kashar cheese with pulsed ultraviolet light
Pulsed ultraviolet light is a potential postprocessing decontamination method which is able to reduce pathogens on solid food surfaces. Cheese surfaces may become easily contaminated with pathogens due to improper handling or contact with unhygienic surfaces during or after processing. In this study, the effects of pulsed ultraviolet light on Staphylococcus aureus and Escherichia coli O157:H7 on fresh kashar cheese were investigated. Pulsed ultraviolet light was applied to kashar cheese for different times (5, 15, 30, 45, 60 s) at 5, 8, and 13 cm from the quartz window in a pulsed ultraviolet light system. Based on the inactivation level, time, and visual evaluation, the most favorable treatment was determined as the 45 s–13 cm treatment (∼44 J/cm2). This treatment yielded about 1.62 and 3.02 log10 reductions (cfu/cm2) for S. aureus and E. coli O157:H7, respectively, while did not alter (p>0.05) the pH, lipid oxidation, and moisture content of kashar cheese, except the color parameters. When 0.5 cm thick kashar cheese was treated with pulsed ultraviolet light at a distance of 5 cm from the quartz window, the highest energy transmittance was found to be about 9.16%. These findings demonstrate that pulsed ultraviolet light has the potential for postprocessing decontamination of semi-hard cheese surfaces.