Modelling the kinetics of Staphylococcus aureus in goat's raw milk under different sub-pasteurisation temperatures

Abstract

In this study, the heat resistance of S. aureus in goats’ raw milk subjected to thermisation temperatures was characterised through tests at various temperatures and modelling the survival curves using the Weibull model, through a two-step and an omnibus approach, which can model a full dataset covering all experimental conditions in one step. The fitting capacity of the secondary models obtained from the two-step approach was reasonable (adj. R² > 0.639) and both demonstrated the negative linear effects of temperature on $\sqrt{\chi }$ (p = 0.0004) and $\sqrt{\beta }$ (p = 0.017). The fitting capacity of the omnibus model was more satisfactory (adj. R² = 0.996) and also hinted at the negative linear effect of temperature on $\sqrt{\chi }$ (p < 0.0001), with the added advantage that, in this model, random effects can be used to account for the variability in the parameters. Our study estimated the significant inactivation parameters and established a model capable of predicting S. aureus behaviour at various temperatures. This information is useful to create time-temperature tables to reach target log reductions of S. aureus in goats’ raw milk to be used by artisanal cheesemakers; hence providing an opportunity to increase the microbiological safety of cheeses made from unpasteurised milk.