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 degrees 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. (c) 2005 Elsevier Ltd. All rights reserved.