Effects of gelatin concentration on the growth parameters of Listeria innocua in a model gel system

In this work, the growth of Listeria innocua was studied responding to the addition of different concentrations of gelatin (see text) model gel system in a modi_ed Brain Heart Infusion medium at 12 C and an initial pH of 6.2. The global number of viable cells as a function of incubation time and the corresponding pH, lactic acid concentration and glucose concentration were measured. Each set of data was fitted with the growth model of Baranyi and Roberts (1994) to estimate the maximum specific growth rate and the maximum cell concentration. Gelatin had a significant e_ect on the growth rate of Listeria innocua, which reduced as the gelatin concentration increased. A tail was observed after a certain concentration of gelatin indicating that there exists a maximum concentration beyond which no further reduction could be observed. There was, however, within the gelatin concentration range studied, no appreciable effect on the maximum cell concentration. A distinct morphological change of colonies was also observed with increasing gelatin concentration.