Steam Treatments: Strategies To Control Pathogen Contamination

Zi Hua

doi:10.7273/000005327

Pathogen contamination on equipment surfaces and food products can cause serious problems. This dissertation comprehensively evaluated the efficacy of steam treatments alone or in combination with low concentrations of sanitizers in removing Listeria innocua biofilms from common food-contact surfaces. Results showed that saturated steam at 100 °C had a rapid kill against L. innocua biofilms, with a 6-sec treatment reducing 2.41 - 3.15 log10 CFU/coupon of L. innocua, depending on the type of surfaces where biofilms formed. However, the steam killing effects were reduced with prolonged exposure. Incorporating peroxyacetic acid (40 ppm, 1 min) before steam treatment (100 °C, 6 sec) reduced more than 6 log10 CFU/coupon L. innocua in biofilm on stainless steel and polyester surfaces while lowering 4.37 log10 CFU/coupon L. innocua in biofilm on rubber. This hurdle combination was less effective on surfaces with wear and/or organic matter, but it still provided more than 5 log10 CFU/coupon L. innocua reduction on stainless steel and polyester and 4.5 log10 CFU/coupon reduction on rubber surfaces under the worst-case scenario. In addition, raising the steam temperature from 100 °C to 142 °C enhanced the effectiveness of steam treatments against L. innocua biofilms on all surface coupons. Similar to steam at 100 °C, steam above 100 °C exhibited reduced kill effects against L. innocua in biofilm after come-up time and at extended exposures, regardless of temperatures and surface materials. Thus, hurdle interventions were further explored to improve the effectiveness of steam treatments. The 1-min contact of peroxyacetic acid or quaternary ammonium compounds at 10 ppm, followed by a short time exposure to steam at 125 °C reduced at least 5 log10 CFU/coupon L. innocua on all surface materials. The effectiveness of steam treatments at 100 - 135 °C was then evaluated on almond kernels, a common food commodity that has been previously linked to multiple contaminations with Salmonella and L. monocytogenes. Results showed that raising the steam temperature and increasing aw of almonds shortened the time needed to obtain a 4-log reduction of L. innocua and Enterococcus faecium NRRL-2354, the known surrogates, in almond kernels. In summary, data collected from this dissertation could provide helpful information to the food industry regarding the effectiveness of steam treatments for controlling pathogen contaminations in food-contact surfaces and food products.

Steam Treatments: Strategies To Control Pathogen Contamination

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