Abstract

This study is related to the isolation and identification of strains of local thermophilic lactic acid bacteria belonging to the species, Streptococcus thermophilus andLactobacillus bulgaricus. These bacteria can exist under extreme conditions of the digestive tract (acidity and high concentration of bile salts) and have a high capacity to degrade lactose. The aim is to produce yoguort with the bacteria that remain viable and active in the digestive tract, so as to enhance lactase activity at the intolerant lactose. The results also show considerable variations between genera, species and strains of the same species in the decomposition of lactose in pure and mixed cultures (Sc.t₅ and Sc.t₃, respectively, with 48 and 42%) (YSLB₂, YSLB₄and YSLB₁, respectively, with 90.44, 87.22 and 84.28%) of initial lactose after 6 h of incubation at 37°C while keeping a level of viability higher than 10⁷ cells/ ml. In the presence of pH (2.5, 4.5 and 6.5), put with or without 0.3% of bile salts, the results are also unmatched. The best cultures will be used to manufacture fermented milks (yoghurts) in order to correct intolerance with lactose in man after having to test them, in a second part, in vivo.

Key words: Lactic acid bacteria, extremophile, intolerance of lactose, digestive tract.