Comparison of sodium hypochlorite and peracetic acid as sanitising agents for stainless steel food processing surfaces using epifluorescence microscopy

The effects of the sanitising agents sodium hypochlorite and peracetic acid on Escherichia coli, Pseudomonas fluorescens and Staphylococcus aureus adhering to stainless steel were compared using epifluorescence microscopy. The bacteria were isolated from chicken carcasses and allowed to adhere to stainless steel coupons for 1 h before being rinsed with sterile distilled water and treated with the sanitising agents at 250 or 1000 mg l(-1) (peracetic acid) or 100 or 200 mg l(-1) (hypochlorite) for 10 min. P. fluorescens showed the greatest adhesive ability, followed by E. coli, while S. aureus adhered in lowest numbers. In all cases, sodium hypochlorite was more effective than peracetic acid in killing or removing the adherent cells. After treatment with either concentration of hypochlorite, the number of adhered cells per field (area 8.66 X 10(-3)mm(2)) was reduced from 118.5, 52.0 and 28.0 to 1.0, 0.0 and 0.0 for E. coli, Pseudomonas fluorescens and Staphylococcus aureus, respectively. These are equivalent to reductions from 13.7 X 10(3), 6.0 x 10(3) and 3.2 X 10(3) to 1.2 X 10(2)cells mm(-2) for E. coli and less than this number for the other two species. A median value of zero was not attained for any of the peracetic acid-treated coupons. This sanitising agent was the least effective against S. aureus, achieving only a little over 50% reduction in viable adhered cell numbers at 250 mg l(-1). In view of the importance of these microorganisms as food contaminants, and on economic grounds, peracetic acid cannot be recommended as the sanitising agent of choice for chicken processing equipment. (C) 2000 Elsevier Science B.V. All rights reserved.