Application of fluorescent techniques to evaluate the survival of probiotic lactobacilli to bile acid

To apply a fluorescent dye as an alternative technique to evaluate the survival of potentially probiotic lactobacilli to bile acids (BA) as first step in the design of probiotic functional foods. The use of lactic acid bacteria (LAB) in the functional food design depends on their ability to survive in the gastrointestinal tract where bile is an important natural barrier. Bile is mainly constituted by conjugated BA, which can be hydrolyzed to free BA and taurine or glycine. Changes in the transmembrane electrical potential (ΔΨ) of probiotic LAB strains due to the effect of conjugated and free BA were measured and showed that the majority of the tested LAB strains had greater sensibility to free BA than to their respective conjugated acids. Variations in the ΔΨ of the microorganism correlated well with bacterial viability determined by standard plate count method. We therefore propose the DiSC(3)-based fluorescent technique as a rapid and effective method to evaluate the resistance of probiotic lactobacilli to bile as first step for strain selection to be included in functional foods.