Surface Decontamination of Hard Cheeses by Pulsed Uv light

Open Access
Can, Fidan Ozge
Graduate Program:
Agricultural and Biological Engineering
Master of Science
Document Type:
Master Thesis
Date of Defense:
September 06, 2013
Committee Members:
  • Ali Demirci, Thesis Advisor
  • Pulsed UV light
  • cheese
  • surface decontamination
  • Listeria monocytogenes
  • Penicillium roqueforti
Effectiveness of pulsed UV- light to inactivate of Penicillium roqueforti and Listeria monocytogenes on packaged and unpackaged cheeses was investigated in this study. Treatment times and the distance from the UV strobe were evaluated to determine optimum treatment conditions. Packaged and unpackaged cheeses were treated from 5, 8, or 13-cm distances. The treatment was performed up to 40, 50 and 60-s from 5, 8 and 13- cm distances, respectively. For P. roqueforti, maximum log reduction was 1.32 log10 CFU/cm2 after 40-s treatment at 5-cm distance on unpackaged cheese and 1.24 CFU/cm2 on packaged cheese at same treatment conditions. The optimum UV-light treatment condition for P. roqueforti inactivation for both packaged and unpacked cheeses were 8- cm distance for 30-s at 8-cm distance, which yielded ~1.1 log10 reduction. Log reductions of L. monocytogenes at the same treatment conditions were about 2.9 and 2.8 CFU/cm2 packaged and unpackaged cheeses, respectively. The temperature changes and total energy were increased directly proportional with treatment time and inversely with distance between UV lamp and samples. The changes in color and lipid oxidation extent were determined at mild (5-s at 13-cm), moderate (30-s at 8-cm) and extreme (40-s at 5- cm) treatments. The color and chemical quality of cheeses did not show significant difference after mild treatments (p>0.05). The plastic material (polypropylene) was evaluated in terms of mechanical properties after mild, moderate and extreme treatments, as well. There was a decreasing trend between elastic modulus data, however there was no significant difference between untreated, mild and moderate treatments (p>0.05). Overall, these results demonstrated that pulsed UV- light has potential to inactivate P. roqueforti and L. monocytogenes on the surface of hard cheeses.