Influence of composition and processing of Frankfurter sausages on the growth dynamics of Listeria monocytogenes under vacuum

Ready-to-eat (RTE) meat products, such as Frankfurter sausages, are often linked to cases of listeriosis, which is a disease caused by the foodborne pathogen Listeria monocytogenes. Frankfurter sausages vary, from manufacturer to manufacturer, in many aspects: (i) composition, (ii) physicochemical characteristics, (iii) background flora, (iv) processing technology and (v) organoleptic characteristics. Some of these factors have been widely investigated for their effect on L. monocytogenes on food products. However, studies on the specific effect of composition and processing technology on L. monocytogenes dynamics between two sausages are lacking. In this study, the growth dynamics of L. monocytogenes on two types of Frankfurter sausages, fresh and in brine, were studied at constant storage temperatures (4, 8 and 12 °C). Additionally, the physicochemical and compositional characteristics of both types of sausages were analysed. In order to study the isolated effect of preservatives, L. monocytogenes growth dynamics, at 4 °C and 30 °C, were studied in two types of liquid systems. These were prepared with the same level of preservatives as in the two types of sausages. Results indicated no major significant differences in physicochemical characteristics for the two types of sausages; but, statistically significant variability was detected in the concentration of preservatives. In liquid systems, the maximum specific growth rate (μmax) remained unaffected by the effect of preservatives, but the lag phase was longer in the system mimicking fresh sausages. In sausages, the 'in brine' type had two-fold higher μmax at all temperatures and shorter lag phase at 4 °C. The presence/absence of sausage skin, which was found to be impermeable from L. monocytogenes cells and was present in the fresh sausage, could explain those differences. In conclusion, this study highlighted the influence of processing factors, and specifically of the sausage casing on L. monocytogenes growth dynamics. Therefore, an edible membrane, which is heat resistant and impermeable to the cells, could be a hurdle strategy to control the microbiological food safety.