Simulator Technique for Assessing the Bacteriological Control of Food Equipment Surfaces by Cleaning Systems

A cleaning simulator is described which permitted assessment of the control of surface bacteria by food equipment cleaning systems. Test pieces were sequentially exposed in test cells to soiling and cleaning solutions over a 2.5-h period and then left untreated for 9.5 h, after which the sequence was repeated. Four test cells received variations of the basic system sequentially within each 12-h period. Temperature and chemical composition of the soiling solutions were accurately controlled. Milk used for soiling was inoculated with two species of bacteria. Test pieces were removed from the test cells and evaluated bacteriologically and gravimetrically. Five bacterial species were studied for their value as soil contaminants; Streptococcus faecalis , Micrococcus luteus , Enterobacter aerogenes , Pseudomonas aeruginosa and Escherichia coli . P. aeruginosa , E. coli and M. luteus were the most resistant to an iodophor sanitizer, while P. aeruginosa and S. fuecalis were most resistant to both a quaternary ammonium compound and chlorhexidene. Studies of growth rates in milk after refrigerated storage for 48 h showed all five organisms suitable for use as milk contaminants. These studies, and other characteristics of these organisms, led to selection of S. faecalis , paired with either E. coli or E. aerogenes as the milk contaminants for simulator experiments.