Food contact surfaces may present a potential health hazard if they are not properly cleaned and sanitized. Contaminated surfaces (e.g. utensils, cutting boards, equipment) have been identified as sources of cross-contamination for food during preparation and when being served to consumers. Therefore, ensuring effective cleaning and sanitization of food contact surfaces may help in the spread of foodborne pathogens and incidence of outbreaks.
The FDA Food Code and NSF International standards mandate that all surfaces/tableware items should be free of food soils and that a minimum microbial reduction of 5 logs must be obtained before surface sanitization could be considered effective. To comply with these standards, food service establishments must clean and sanitize food contact surfaces either manually or mechanically. Unfortunately, the standards set for these ware-washing methods specifically address the reduction of bacterial numbers from food contact surfaces, and not viruses. Therefore, information regarding the effectiveness of these standards against viruses needs to be elucidated. The first part of this dissertation (Chapter 2) compared the efficacy of sodium hypochlorite (chlorine) and quaternary ammonium compound (QAC) in reducing bacterial populations (Escherichia coli K-12 and Listeria innocua) and murine norovirus (MNV-1) counts on different food contact surfaces (ceramic plates, stainless steel forks and drinking glasses). Each microorganism was separately inoculated into 2% reduced fat UHT milk and creamcheese spread. The milk was used to contaminate the drinking glasses and the spreadable cream cheese was used on the ceramic plates and forks. All tableware items were manually and mechanically washed and sanitized. Bacterial and viral counts were then determined on the surface of each tableware item using the plaque assay and plate count methods, respectively.
This study found that QAC and sodium hypochlorite sanitizers had the ability to produce greater than/equal to 5 log reductions on both E. coli and L. innocua in manual and mechanical ware-washing operations. However, they were unable to produce the same level of antiviral activity (less than/equal to 3 logs) under similar conditions irrespective of the nature of the tableware item and the ware-washing protocol.
The second part of this dissertation (Chapter 3) evaluated the efficacy of the manual and mechanical ware-washing protocols to remove caliciviruses from food contact surfaces (ceramic plates, stainless steel forks and drinking glasses). Porcine sapovirus (PoSaV) was used as a surrogate for both noroviruses (NoVs) and sapoviruses (SaVs). The tableware items were contaminated with the milk (drinking glasses) and cream cheese spread (ceramic plates and forks) inoculated with PoSaV. These were manually and mechanically washed and sanitized with different sanitizing solutions (chlorine and QAC). Tap water was used as the control sanitizing solution. After the ware-washing operations, the viral counts on the surfaces were determined by 50% tissue culture infective dose (TCID50). The chlorine sanitizer was able to reduce PoSaV by approximately 2 logs when exposed to higher temperatures during mechanical ware-washing (49ºC vs. 43ºC during manual ware-washing). The viral reductions achieved with the other sanitizers (QAC and control) were not significant (less than 1 log).
The third part of this dissertation (Chapter 4) investigated the effect of different sanitizers [chlorine-based sanitizers (bleach and Chlor-Clean), QAC and tap water] on their abilities to remove milk samples from underlying ceramic and glass surfaces. Three types of milk samples were tested in this study: 1) plain milk; 2) milk inoculated with MNV-1; and 3) milk inoculated with PoSaV. Atomic force microscopy (AFM) was used to determine the thicknesses of the milk films left after the surfaces were mechanically washed and sanitized. Results from this study suggested that milk samples contaminated with viruses tend to adhere to a greater extent (thicker films) than non-contaminated milk and that common sanitizing solutions (chlorine-based and QAC sanitizers) appeared not to effectively remove milk-virus deposits from simulated food contact surfaces.