Influence of UV-C radiation on the treatment of Minas Frescal cheese inoculated with Escherichia coli and Staphylococcus aureus

Abstract

Short-wave ultraviolet (UV-C) radiation is a non-thermal technology recognised for its antimicrobial effect and lower investment and maintenance costs compared to conventional preservation methods, in addition to the advantages of minimal nutrient loss and non-formation of residual toxic compounds. The aim of this study was to evaluate the effectiveness of UV-C radiation in inactivating E. coli and S. aureus inoculated in sliced Minas Frescal cheese samples. The sensitivity of the microorganisms to UV-C treatment was tested in vitro by subjecting the strains, inoculated in selective culture media, to six different doses (0.037 J/cm²; 0.123 J/cm²; 0.199 J/cm²; 0.263 J/cm²; 0.326 J/cm²; 0.520 J/cm²). All doses tested in vitro increased logarithmic reduction. Dose 6 (0.520 J/cm²) provided a reduction of six logarithmic cycles in both microorganisms tested (6.72 log CFU/g for E. coli and 6.93 log CFU/g for S. aureus). However, the lowest doses with significant difference and relevant logarithmic reduction, dose 3 (0.199 J/cm²) and dose 5 (0.326 J/cm²), were selected for the treatment of the inoculated cheese slices, minimizing possible physicochemical and sensory changes. After UV-C treatment, the cheese slices were stored at 4 °C for 15 days for microbiological analyses. A reduction of one logarithmic cycle was observed at both doses tested for both strains studied (1.1–1.2 log CFU/g for E. coli and 0.89–1.26 log CFU/g for S. aureus). It was concluded that the effect of UV-C light on sliced Minas Frescal cheese, despite its effectiveness in reducing the concentration of E. coli and S. aureus, may be affected by intrinsic factors of the cheese that interfere with the light incidence.