Characterisation and technological properties of psychotropic lactic acid bacteria strains isolated from Tunisian raw milk

Abstract

A total of 102 wild lactic acid bacteria (LAB: 32% Lactococcus ssp. lactis, 23% Lactobacillus plantarum, 22% Lactobacillus pentosus, 7% Leuconostoc mesenteroides, 5% Lactobacillus brevis), isolated from Tunisian refrigerated raw milk obtained from collected centres, were screened according to their antimicrobial activities against spoilage and undesirable micro-organisms. Nineteen isolates having the most important antimicrobial activities were selected. Amplification of 16S/23S spacer regions of these selected LAB yielded two amplicons for Lactobacillus genus and only one amplicon for both Lactococcus and Leuconostoc. However, three strains of Lactococcus and two strains of Leuconostoc were eliminated because they present two amplicons. Hence, only fourteen strains were retained, they were also characterised in respect to their technological properties (lipolytic activities, proteolytic activities, enzymatic activities, acidifying capacity and antibiotic resistance). Acidification (degree Dornic) varied from 24.5 ± 0.07 to 37.5 ± 0.07 after 10 h. Low proteolytic capacity was detected for all strains using different substrates (oPA, TNBS and azocasein methods). Lipolytic capacity didn't surpass 0.3 ± 0.03% fatty acids for all strains. Lipase and esterase lipase activities were practically non-existent for most selected LAB. The behaviour of these strains against various antibiotics was also found to be similar.