Effects of inulin, fructooligosaccharides/glucose and pH on the shape of the death kinetic of Lactobacillus reuteri DSM 20016

The viability of Lactobacillus reuteri, Lb. delbrueckii subsp. bulgaricus and Lb. paracasei was assessed in a laboratory medium containing inulin (5 g L−1) or glucose + FOS (fructooligosaccharides) (2.5 + 2.5 g L−1). Data were modelled through the Weibull equation pinpointing that prebiotics determined a decrease in the shape parameter. In the 2nd step, L. reuteri was used as the test microorganism; pH, storage temperature and the amounts of FOS + glucose and inulin were combined through a 4-variable/5-level central composite design. Temperature, pH and glucose + FOS affected the microbiological shelf life; inulin was not significant. The maximum value of shelf life was found at pH 8.5 and with 5.0 g L−1 of glucose + FOS. The combination of pH and prebiotics affected the shape parameter with a shift from a convex to a concave trend and vice versa: their effect was different depending on the use of a single prebiotic or a mix.