Identification of probiotic cultures in food samples

Abstract

Probiotic cultures are used increasingly in dairy products. Confusion occurred due to false declarations and the uncritical selection of strains. Efficacy of probiotic cultures depends on special properties of single strains, however. Over the last 30 years, own experience was made with strains of the genera Lactobacillus and Bifidobacterium, especially out of the groups of Lactobacillus acidophilus, Lactobacillus casei, and Lactobacillus reuteri/fermentum which were collected from commercial probiotic food samples as well as from pharmaceuticals and nutrients for animals. They were compared with reference strains from culture collections. Phenotypic criteria revealed a grouping of isolates at genus level and, in most cases, a correct identification of species, too. False declarations of cultures used world-wide as probiotics could thus be detected. In order to confirm questionable species or to characterise specific strains within a species, molecular-based methods had to be applied. Good results were obtained by (1) SDS-PAGE of soluble proteins of cells, (2) RAPD-PCR, (3) PFGE-technique and (4) dot blot hybridisation methods using gene probes. Costs and workload differed considerably. SDS-PAGE and RAPD-PCR required data bases, dot blot hybridisation worked faster and more productively. For confirmations, at least one molecular-based method has to be applied.