Sigmoidal thermal inactivation kinetics of Listeria innocua in broth: influence of strain and growth phase

Listeria innocua inactivation was studied within the temperature range 52.5-65.0 °C, comparing two different strains (10528 and 2030c) and two growth phases (exponential and stationary). Survival curves may present a sigmoidal behaviour, with an initial shoulder (L), followed by a maximum inactivation rate (k_max) period and a final tailing tendency. A Gompertz-inspired model was used to fit experimental data, and kinetic parameters (L, k_max and tail) were estimated by non-linear regression analysis. The influence of temperature, growth phase and strain on kinetic parameters was studied using a 2³ factorial experimental design. Results showed that temperature and growth phase were the most significant variables affecting the kinetic parameters. Listeria thermal inactivation varied from a log-linear tendency till a pronounced sigmoidal behaviour, depending on the studied factors.