Isolating the effect of fat content on Listeria monocytogenes growth dynamics in fish-based emulsion and gelled emulsion systems

Abstract

The influence of food matrix fat content on growth kinetics of bacteria is quite complex and, thus far, not fully elucidated, with different studies reporting contradictory results. Since results in studies involving real food products are possibly influenced by variations in compositional and physicochemical properties, there is a need for systematic studies in artificial food model systems among which the influence of fat content is effectively isolated. In this study, the isolated effect of a gradual increase in fat content, in the range of 1–20% (w/w), on the growth dynamics of Listeria monocytogenes in fish-based emulsion and gelled emulsion model systems was investigated at 4, 7 and 10 °C. Growth parameters estimated by the Baranyi and Roberts model were compared among the different model systems. Overall, an increase from 1 to 5% fat resulted in a significant reduction of the lag phase duration λ in both model systems at all studied temperatures, while a further increase in fat content did not significantly affect λ. The relationship between the fat content (%) and the maximum specific growth rate μmax was more complex, following the same trends for both emulsions and gelled emulsions and tested temperatures, i.e., (i) μmax was higher at 5% than at 1% fat, (ii) μmax was lower at 10% than at 5% fat, (iii) μmax at 20% fat was higher than or equal to μmax at 10% fat, and (iv) μmax was the highest at 5% fat. Based on these experiments, fundamental knowledge was provided which could lead to the development of food matrix-related factors describing the influence of fat content in future predictive modeling tools which include food microstructural elements. Such models could increase the accuracy of the shelf-life estimation for fat-containing foods, in turn resulting in improved food safety.