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

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.