Impact of meat residues on effectiveness of chlorine dioxide gas against Listeria monocytogenes biofilms

Post-process contamination of ready-to-eat (RTE) meat products with Listeria monocytogenes due to inadequate sanitation measures is a major area of concern for food safety. Biofilm formation and presence of organic and inorganic residue in hard to clean crevices/surfaces leads to reduced effectiveness of sanitizers. A zero tolerance policy has been implemented for Listeria monocytogenes in selected RTE products. Since most Listeria contamination in RTE foods is linked to environmental sources, there is a need to explore the application of novel sanitizers, such as chlorine dioxide (CD), for sanitation. This research evaluated the impact of meat residues on the effectiveness of CD gas against Listeria monocytogenes biofilms. Four day old Listeria monocytogenes biofilms were developed on stainless steel (SS 304) coupons and treated with and without the presence of meat residues. Complete inactivation of Listeria biofilm cells resulted after CD gas treatment of 1mg/l for 90 min. and 2 mg/l for 70 min. Scanning electron microscopy revealed breaking of the polysaccharide layer and evidence of material on surface of the cells after treatment. Low levels of CD (0.3 mg/l CD gas and 7 mg/l aq. CD solution) treatment for 10 min. resulted in similar log reductions as compared to 50 mg/l of sodium hypochlorite (SHC) treatment. Pork sarcoplasmic proteins and fat were applied on top of biofilms before treatment. CD gas (2 mg/l CD gas at 75% RH) was more effective in presence of low pork fat residue (31 mg/coupon) as compared to pork protein residue (12.6 mg/coupon). Results showed that CD gas was able to diffuse through a layer of liquid pork fat. Dried beef frankfurter exudate (BFE) significantly reduced the microbial reduction after a 2 mg/l CD gas treatment for 10 min. Combination of beef protein (10 mg/ml) and corn syrup (6.5%) resulted in reduced microbial reduction after CD gas treatment. Aqueous CD was most reactive with beef protein and least with corn syrup and beef fat. Under refrigeration conditions and in presence of BFE residue (300 μl), 100 mg/l aqueous CD rapidly reduced Listeria biofilm cells (\u3e3 log CFU/cm2) at 1 and 5 min treatment times as compared to 200 mg/l quaternary ammonium compound (QAC) and 100 mg/l SHC sanitizers. In summary, CD treatment can be used effectively to inactivate Listeria biofilm cells in presence of low levels of meat residues tested