Evaluation des aptitudes technologiques des souches autochtones de bactéries lactiques

Abstract

Fermented dairy products are very popular and appreciated by consumers for their organoleptic and nutritional characteristics. Lactic acid bacteria are responsible for the sensory properties of these products, as well as developing certain technological properties and increasing their shelf life. For this reason, these bacteria are widely used as processing means in the food industry to transform a wide range of raw materials to get a wide variety of products. However, use of autochthonous LAB strains for directed fermentations demands caution due to their potential to produce undesirable metabolites or harbor antibiotic resistance genes. In the present study, 22 strains of LAB were tested for different technological properties. The results showed that most strains did not have hemolytic activity, except for L. lactis BL22, which showed positive β-hemolysis. Most of the strains were mesophilic (they grow best at 30 °C) and could tolerate acidic (pH 3.5–4.5) and alkaline (up to pH 9.5) conditions. One strain, L. curvatus BL1, could grow even at pH 2, and another, L. garvieae BL15, could grow at low temperature (2 °C). Some strains also grew well in salty environments (L. curvatus BL1; L. plantarum BL5, BL7; L. rhamnosus BL6, BL13, BL20; L. garviae BL15, L. paracasei BL17, L. lactis BL19). When the strains were tested in UHT milk, the acidification varied between them. Some strains like L. paracasei BL10, L. parabuchneri BL11, and L. lactis BL19 produced high acidity (more than 83 °D) and showed good milk protein coagulation. Several strains, including L. rhamnosus BL13, BL14, BL18, BL20; L. mesenteroides BL19; and L. paracasei BL10, were able to produce acetoin, a compound that gives a buttery flavor to fermented products. Antibacterial activity tests showed that L. rhamnosus BL6, L. plantarum BL5, and L. rhamnosus BL7 had strong inhibitory effects against harmful bacteria such as Staphylococcus aureus, Escherichia coli, Listeria monocytogenes, Pseudomonas aeruginosa, and Bacillus subtilis. In conclusion, this evaluation helped to select some strains (L. palantarum BL7, L. parabuchneri BL11 et L. rhamnosus BL13) that show potential for future pilot-scale production.