Predictive modelling and validation of Pseudomonas fluorescens growth at superatmospheric oxygen and carbon dioxide concentrations

Abstract A model was developed to describe the growth of the spoilage organism Pseudomonas fluorescens LMG 7207 at different gas conditions containing high oxygen and elevated carbon dioxide concentrations. The bacteria were grown on a nutrient agar surface at 7 °C. Three carbon dioxide levels (0%, 12.5% and 25%) were combined with different levels of high oxygen concentrations (above 20%) based on a mixture design. High O2 and CO2 concentrations decreased the maximum specific growth rate ( μ max ) and prolonged the lag time ( λ ). The model parameters were estimated in a one-step nonlinear least-squares regression. Two overall models were compared: (1) the Baranyi equation with a first-order linear response surface model to describe μ max and λ as a function of O2 and CO2 and (2) the Baranyi equation with insertion of the first-order equation for μ max and with λ linearly related to μ max - 1 . Both models described the growth very well. To assess the validity of each overall model, an additional experiment with six gas conditions was carried out. The best correspondence between observed and predicted growth data was obtained with model 1, as based on different validation parameters (MSE, adjusted R 2 , Bias and Accuracy factors). The 95% confidence limits for a new prediction were estimated for each validation gas condition using a Monte Carlo procedure.