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 ºC, 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 (kmax) period and a final tailing tendency. A Gompertz-inspired model was used to fit experimental data, and kinetic parameters (L, kmax 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