Influence of a gel microstructure as modified by gelatin concentration on Listeria innocua growth

The effects of a gelatin gel microstructure as modified by increasing concentration of the gel agent on Listeria innocua growth is studied in a modified BHI medium, mimicking a (semi-)solid food product, at 12 °C and an initial pH of 6.2. Viable counts of the cells were followed as a function of incubation time. The cell growth data were fitted with a classical growth model to estimate the maximum specific growth rate and maximum cell concentration. The micro-colony morphology was also examined with light microscopy and image analysis techniques. The gel microstructure had a slight effect on the growth rate, which generally reduced as the gelatin concentration increased. However, within the range of 50 and 200 g L− 1 and beyond 300 g L− 1 gelatin, the growth rate remained approximately constant and was not affected by the increase in gelatin concentration. A distinct morphological change from large and diffuse through compact and round, up to a more compact, elliptic micro-colony was observed with increasing gelatin concentration. On the contrary, no change in maximum cell concentration was observed within the gel concentration range studied.