Response of some microorganisms to ultraviolet treatment on fresh-cut pear

Abstract

Ultraviolet energy at a wavelength of 253.7 nm (UV-C) was investigated for its microbicidal effects on pear slices with and without peel. Effectiveness of UV-C light against Listeria innocua ATCC 33090, Listeria monocytogenes ATCC 19114 D, Escherichia coli ATCC 11229, and Zygosaccharomyces bailli NRRL 7256 individual strains was tested in both types of pear slices. In a second experiment, strain cocktails of Listeria (L. innocua ATCC 33090; L. innocua CIP 8011 and L. welshimeri BE 313/01), L. monocytogenes (L. monocytogenes ATCC 19114 D, L. monocytogenes ATCC 7644), and yeasts (Z. bailii NRRL 7256, Zygosaccharomyces rouxii ATCC 52519, and Debaryomyces hansenii NRRL 7268) were also used as inocula and compared with single-strain responses. Inoculated pear slices were exposed to a UV-C dose range between 0 and 87 kJ/m2 and enumerated to determine log reductions of microbial populations. Overall, as UV-C dose was increased (increasing the time of exposure), more inactivation was observed for all species assayed. UV-C irradiation appeared to improve microbial inactivation in pear slices without peel. In most experiments, great log reduction rates were observed at doses between 0 and 15 kJ/m2 . Inactivation kinetics was successfully fitted using a Weibullian distribution of resistances model. Narrow frequency shapes strongly skewed to the right were obtained. This model offers improved tools for designing and implementing UV-C light treatment and assessing the impact of some microorganisms’ disease.