A novel experimental setup studying the effect of high CO2 & low O2 on Listeria monocytogenes growth under controlled conditions

Introduction Modified atmosphere packaging (MAP) is the replacement of the atmosphere surrounding the product with an alternative gas mixture (e.g. CO2/O2/N2). This technology works better with low temperatures, resulting in the extension of the shelf life of food. However, Listeria monocytogenes ra...

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Hauptverfasser: Oğuz, Seren, Bonanni, Eleonora, Kuuliala, Lotta, Somrani Achouri, Mariem, Devlieghere, Frank
Format: Tagungsbericht
Sprache:eng
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Zusammenfassung:Introduction Modified atmosphere packaging (MAP) is the replacement of the atmosphere surrounding the product with an alternative gas mixture (e.g. CO2/O2/N2). This technology works better with low temperatures, resulting in the extension of the shelf life of food. However, Listeria monocytogenes raises concerns when it comes to refrigerated foods because it can grow at low temperatures. The combination of MAP using C02-rich and O2-free gas mixtures with refrigeration was found inhibitory for the growth of L. monocytogenes. However, in the literature, there is a very limited amount of studies available where microbial growth was monitored during storage and under constant controlled atmosphere conditions so far. For this study, a new setup consisting of gas-washing bottles was developed to investigate the growth of L. monocytogenes by maintaining constant well-defined atmospheres during storage. Thus, this work aims to investigate the impact of high CO2 and low O2 on L. monocytogenes in a liquid growth medium at low temperature and under well-controlled conditions provided by the novel gas washing bottle incubation system. Materials and Methods In this study, L. monocytogenes isolated from smoked salmon inoculated (3.0 log CFU/ml) in brain heart infusion (BHI) was investigated at 4℃ for 13 days under different MAP conditions (O2%/CO2%: 0/20, 0/40, 0/60). BHI broth was placed in a gas washing bottle and three bottles were connected in series to test one gas combination. Gas was introduced to the bottles by the flushing technique once a day to keep dissolved gas in BHI at the desired concentration. On the other hand, sampling was done before each flushing. Control bottles with an air atmosphere were also included. Discussion This study confirmed that a lag phase is clearly seen in the growth curve of L. monocytogenes treated with investigated CO2 levels at 4℃. In addition, the microbial counts of L. monocytogenes within 13 days increased from 3.0 to 5.8 log CFU/ml and 3.0 to 4.8 log CFU/ml with 20% and 60% CO2 respectively. This was consistent with a previous study that observed the growth rate of L. monocytogenes decreased with increasing CO2 at 4℃ (Farber et al., 1996). The new setup developed during this study was found to be successful in investigating the inhibitory effect of CO2 on the growth of L. monocytogenes, by keeping the desired atmosphere condition constant. With this novel setup, it will be expected that the impact of trace levels of O2 on the