Purpose: To investigate the biofilm formation of foodborne pathogens on the surface of stainless steel and to evaluate the efficacy of temperature and chemical sanitizers on the removal of biofilms.
Methods: Mixtures of L. monocytogenes, S. Typhimurium, and STEC were separately inoculated on stainless steel coupons. The coupons were then either treated by heat (60, 80, and 100°C) for 10 min or by a chemical sanitizer for 10 min, or by both. The sanitizers used were a quaternary ammonium compound, lactic acid, sodium hypochlorite, hydrogen peroxide, levulinic acid (LVA), sodium dodecyl sulfate (SDS), and three different concentrations of LVA plus SDS. The treated coupons were subsequently enriched in different broths. The attached cells were dislodged by using the bead vortex method.
Results: Ca. 8.6 to 9.2 log CFU/coupon of pathogens grew in the biofilms after 72h of incubation at 100% relative humidity and 21°C. Inactivation was greater when the temperature was increased. Increasing the temperature to 80°C resulted in significant (P < 0.05) reduction of 1.0, 1.4, and 1.7-log reduction of the pathogens, respectively. The three pathogenic cell numbers were reduced by 0.3 to > 6.9 log CFU/coupon within 10 min when treated with QAC (150 ppm), SHC (100 ppm), HP (2%), LVA (3%), SDS (2%) and LVA+SDS (0.5% LVA+0.05% SDS, and 1% LVA+0.1% SDS). More (P < 0.05) colonies were recovered from TSA than selective plates after LA (3%) treatment. When 80ºC+LA (3%) and 3% LVA+2% SDS were applied, all three pathogenic cell numbers were reduced to an undetectable level (negative by enrichment cultures).
Significance: Results revealed that 80°C+ LA (3%) or 3% LVA+ 2% SDS sanitizer can effectively reduce foodborne pathogenic biofilms by >6.9 log CFU/coupon on stainless steel.