Comparison of detection methods used to determine Escherichia coli and meat exudate removal from stainless steel surfaces following different physical cleaning methods.

Food products can be contaminated by residual organic materials and food-borne pathogenic microorganisms through contact with biofouling present on surfaces. Efficient cleaning is needed to maintain hygienic requirements and for quality assurance of food contact surfaces. To evaluate the efficacy of cleaning procedures, it is essential to use reliable detection and quantification methods that can detect both organic material and microorganisms retained on surfaces. Repeated fouling with both organic material (meat exudate) and microorganisms (Escherichia coli) on 304 2B finish stainless steel surfaces was carried out. The surfaces were then cleaned using either a soak, spray or wipe method (in water) in order compare various biofouling detection methods. Following enumeration of the microorganisms by plate counting, the results demonstrated that the soak and spray washes were the best cleaning methods, whereas the wipe clean produced the least hygienic surface. ATP bioluminescence further demonstrated that the spray cleaned surface was the most hygienic followed by the soaked cleaned surfaces. However, percentage coverage counts demonstrated that the number of retained cells on following the soak wash was the greatest (77.38 % after 30 washes) and the amount of organic material retained was greater than 50% on all the surfaces, and was not significantly different between the different types of cleans or number of washes. Visualisation of the surfaces using epifluorescence microscopy and scanning electron microscopy demonstrated that the soak clean was the least hygienic in terms of bacterial retention. This suggests that the biofouling on the surface was difficult to remove following the soak cleaning method. UV detection demonstrated that it was difficult to detect organic material, regardless of the cleaning method used. However, when using more intense UV at selected wavelengths, the 330 nm - 360 nm illuminated the retained biofouling on the surfaces with the greatest intensity. The use of the different cleaning assays resulted in differences in cell and organic material distribution across the surfaces. The recorded level of contamination varied depending on the detection method used in this study. Our results highlighted that, in addition to the quantification method, visual images and quantification may help to better understand the fouling process on surfaces since certain cleaning methods may result in organic material being difficult to remove and detect