Findings published in the journal Food Pathogens and Disease show that L. monocytogenes populations were significantly reduced on all belt types irrespective of UV light intensities and times of exposure.
L. monocytogenes as a food-borne pathogen has significant public health and economic impacts with manufacturers of ready-to-eat foods required, under EU regulation, to examine the processing environment for microbe as part of their hazard analysis critical control point (HACCP) approach and sampling schemes.
The food hazards posed by the bacteria are especially due to its ability to grow over a broad temperature range, a characteristic enabling the pathogen to modify its membrane composition to maintain membrane fluidity.
“It survives and grows on conveyor belts (CBs) and can secret extracellular polysaccharides to adhere and form biofilms. These biofilms are difficult to clean especially from surfaces like CBs due to their intricate design and are subsequently disseminated onto foods during processing,” said the US researchers.
Conveyor belts, said the US researchers, are often difficult to clean and require rigorous sanitation programs for decontamination. They maintain that existing sanitation methods are often not sufficient to remove bacterial cells and their biofilms from food contact surfaces.
Most of the proceeding research on the attachment of Listeria to inert surfaces has tended to focus on stainless steel, said the authors, who are based at the Auburn and Iowa State Universities. They said that, as a result, this study was conducted to determine the efficacy of UV against L. monocytogenes on CBs made of different materials.
The method
A four-strain cocktail of L. monocytogenes (serotypes 3A, 4A, 4B, and 4C) was made to give a suspension of approximately 107CFU/mL.
Conveyor belts evaluated were made from four different types of materials: Belt type 1 being Ropanyl DM 8/2 A2+04, Belt type 2 being Volta FRMW-3.0, Type 3 being Volta FRMB-3.0 and Type 4 being Ropanyl DM. They were all inoculated with 1mL of the four-strain cocktail (107CFU/mL) of the bacterial suspension.
The CBs were treated with UV light (254nm) for one and three seconds at 5.53 and 5.95mW/cm2.
Three replications of the experiments were conducted, added the authors.
Results
Two-way analysis of variance of survival populations of L. monocytogenes showed bacterial counts were reduced to below detection limits on belt types one, two, and three after exposure to 5.95mW/cm2 UV light intensity for three seconds.
Belt 4 showed survival populations of L. monocytogenes ranged from 1.42 to1.73 log10CFU/cm2 after UV light treatment for one and three seconds.
The authors conclude that UV light can be effectively used to reduce L. monocytogenes contamination on CBs.
Another recent study looking at one specific sandwich production plant, published in the journal Food Control, found that particular strains of L. monocytogenes persisted for more than nine months in the processing environment, in particular on slicers and conveyor belts.
The authors of that research, who are based at the Institute of Food Safety and Hygiene in Zurich, said their results showed that bread feeding machines, slicers, conveyor belts and water hoses are the areas most at risk for contamination by the bacteria and they recommend continuous monitoring of plant equipment and environment to ensure an early warning system for processors.
Source: Foodborne Pathogens and Disease
Published online ahead of print: doi:10.1089/fpd.2009.0464
Title: Efficacy of Ultraviolet Light Exposure Against Survival of Listeria monocytogenes on Conveyor Belts
Authors: A. Morey, S.R. McKee, J. S. Dickson, M. Singh