Comparison between the resistance of benzalkonium chloride-adapted and -nonadapted biofilms of listeria monocytogenes to modified atmosphere packaging and nisin once transferred to mussels

Abstract

Benzalkonium chloride-adapted and -nonadapted Listeria monocytogenes biofilm cells were transferred by contact to cooked or live mussels and packed in rich CO2 and O2, respectively. The viabilities of transferred cells during storage of these packed samples at 2.5°C were compared. In addition, in cooked mussels the combined effect of CO2 and nisin against the survival of L. monocytogenes was also studied by using a first-order factorial design. The results obtained demonstrated that biofilms formed by benzalkonium chloride-adapted L. monocytogenes cells could be more resistant to the application of modified atmospheres rich in CO2 and nisin once they have been transferred to cooked mussels by contact (simulating cross-contamination). This implies an increase in the risk associated with the presence of these cells in food processing plants. Significant empirical equations obtained after 7, 11, and 20 days showed an inhibitory effect of CO2 and nisin against L. monocytogenes. However, a significant positive interaction between both variables highlights an incompatibility between CO2 and nisin at high concentrations. Results also demonstrated that L. monocytogenes could persist after cross-contamination during the processing of live mussels, so L. monocytogenes is of concern as a contaminant in live mussels packaged in high-O2 atmospheres.