Tolerance of Lactobacillus casei, Lactobacillus paracasei and Lactobacillus rhamnosus strains to stress factors encountered in food processing and in the gastro-intestinal tract

- High diversity of L. casei, paracasei, rhamnosus strains to withstand stress conditions was observed.
- Strains from wine, faeces and sourdough niches showed the best stress tolerance properties.
- Hierchical Cluster Analysis highlighted that 13 strains fulfilled all the pre-requisites for probiotic use.
- Screening methods for selecting promising candidates for industry application were defined.

This study was aimed at selecting novel strains of Lactobacillus paracasei, Lactobacillus casei and Lactobacillus rhamnosus for their capability to withstand different stress factors encountered in food processing and in the gastrointestinal tract. In spite of the extensive use of Lactobacillus strains in food applications and as commercial probiotics, there is little information on the diversity in the stress tolerance within these species. In this work 108 L. paracasei, 68 L. rhamnosus and 8 L. casei strains, isolated from different sources (dairy and meat products, sourdoughs, wine, beverages, vegetables and human body) and geographical regions were screened for tolerance to acid, bile salts, high osmolarity and capability to grow at different non-optimal temperatures and survival after exposure to refrigeration or freezing.The study highlighted a noticeable heterogeneity in the ability of the strains to withstand harsh growth conditions suggesting that different stress factors should be applied to identify the most promising candidates for technological uses. In this investigation thirteen strains, isolated from wine, human faeces and sourdough niches, that showed better tolerance to high acidity, bile salts and NaCl, thus more interesting for being industrially exploited, were selected.