CO2 and pH influence the effect of O2 on the growth of Listeria monocytogenes at refrigeration conditions.

Ensuring food safety in the transition towards more sustainable packaging is critical, particularly given the persistent threat of Listeria monocytogenes in refrigerated modified atmosphere packaging (MAP). Although combining high CO2 and low O2 in refrigeration has been an effective strategy for controlling this pathogen, very little information is available on the effect of the presence of O2 on the growth of L.monocytogenes. This presence during storage is very difficult to avoid when switching to more gas permeable packaging materials. To better refine food safety strategies, extensive quantitative data under controlled conditions are needed to clarify the role of O2 and its interactions with key stressors (CO2, temperature, and pH). Thus, this study aims to analyze the individual effect of O2 and its combined effect with these key factors on L.monocytogenes behavior in a liquid medium under well-controlled atmospheres (60/0/40, 60/20/20, 60/2/38, 0/20/80, 0/0/100-CO2/O2/N2%) at different pH values (7.7, 6.2) and temperatures (4, 7 °C) through a gas-washing bottle incubation system (GBIS). Despite earlier reports suggesting no effect, O2 increased growth in CO2-free environment, which was more pronounced at 7 °C than at 4 °C. Moreover, lowering the pH from 7.7 to 6.2 enhanced the observed growth-increasing effect of O2. Most importantly, 60% CO2 (pH = 6.2) suppressed the effect of O2; even 20% O2 decreased maximum growth rate in the presence of CO2. Overall, this study shows a complex interaction between stress factors influencing the effect of O2 on L.monocytogenes growth.