REDUCTION OF listeria monocytogenes, escherichia coli AND zygosaccharomyces bailii POPULATION IN PEAR BY ULTRAVIOLET LIGHT

SCHENK, M.; GUERRERO, S.; GOMEZ, P.; ALZAMORA, S.M.

Chicago, EEUU

Congreso; IFT 2007 Annual meeting; 2007

Institute of Food Technologists

UV-C radiation has been approved for use as disinfectant for surface treatment of food. But its potential for commercial use in fruit and vegetables would depend on its ability to sanitize without causing deterioration of quality.This study was aimed to investigate the effect of UV-C doses on the inactivation of L. monocytogenes; E. coli and Z. bailii in pear surface with and without peel.Pears were sliced into 3 mm thick disks (3 cm in diameter). Some disks maintained the peel. All discs were inoculated with a mixed-strain suspension of Listeria monocytogenes ATCC 19114D and ATCC 7644, and Escherichia coli atcc 11229 or Zygosaccharomyces bailii suspensions (~106 CFU/ml). The disks were placed at 10 cm distance from two UV-C lamps (30 W, 254 nm) inside a cabinet. The UV-C intensity was measured by the iodide-iodate chemical actinometer. The UV-C dose was varied between 0 and 66 kJ/m2 by altering the exposure time up to 15 minutes. Four disks of each duplicate experiment were analyzed for survival microorganisms at each treatment time by pour plating in specific culture media for each type of microorganism.UV-C treatments decreased microbial populations between 2 and 3 log cycles after 15 minute treatments. E. coli was the most sensible specie. The presence of peel in the fruit notoriously changed the observed inactivation pattern. UV-C was more effective at reducing microbial counts on the surface of pear without peel than on pear with peel. For pear slices without peel, UV-C doses higher than 20 or 40 kJ/m2 (according to the specie) did not further reduce microbial population to a lower degree and the inactivation curves exhibited a well defined tail.This study gives useful quantitative information regarding the UV-C dose required to effectively reduce the number of the microorganisms assayed on the surface of pear.