The generation time was proposed as a tool to investigate themicrobial dynamic either in pure or mixed cultures, in fact this way was used to demonstrate the stimulating effect of inulin on the growth of bifidobacteria (Bruno et al., 2002), while for lactobacilli the reference is very poor to this respect. Prebiotics are added to probiotic foods to selectively stimulate the growth of selected probiotics such as bifidobacteria. Because lactobacilli are increasingly used in probiotic foods, it was important to know if the growth of lactobacilli is also stimulated because of prebiotics. In this study there was a decreased doubling time with both the two vegetable substrates used. This suggests that these substrates can stimulate the growth of the specific tested Lactobacillus strains in probiotic products duringmanufacturing and storage and possibly in the gastrointestinal tract.