Using a simplex centroid to study the effects of pH, temperature and lactulose on the viability of Bifidobacterium animalis subsp. lactis in a model system

• Lactulose reduced the viability loss of B. animalis subsp. lactis.
• Lactulose induced a shoulder phase.
• Lactulose could interact with pH.

This paper reports on the effects of lactulose (0–10 g/l) on Bifidobacterium animalis subsp. lactis, along with the influence of pH (4.5–8.5) and temperature (15–45 °C); the three factors were combined through a simplex centroid. The experiments were performed in a laboratory medium and the data of cells counts were modeled through the Weibull equation for the evaluation of the first reduction time, the shape parameter and the death time. These fitting parameters were used as input values to build a desirability profile and a second-order model through the DoE approach (Design of Experiments). The medium containing glucose was used as control.The prebiotic enhanced the viability of the microbial target, by prolonging the first reduction time and inducing a shoulder phase in the death kinetic; moreover, in some combinations the statistical analysis highlighted a kind of interaction with the pH.