Characterisation of lactic acid bacteria isolated from artisanal Egyptian Ras cheese

Abstract

Wild LAB (188 strains) isolated from artisanal Egyptian Ras cheese including Lactococcus (15), Lactobacillus (95), Enterococcus (77) and Pediococcus (1) were characterised for biochemical and production characteristics related to their technological performance. All Lactococcus (subsp. lactis and cremoris) were able to grow at 40°C and in the presence of 4% NaCl. Six L. lactis subsp. lactis, one strain of subsp. cremoris and 95% of Lactobacillus strains were salt-tolerant, as they were able to grow in 6.5% NaCl. Twenty percent of lactococci, 21% of lactobacilli and 43% of enterococci showed a medium acidification rate, one strain of Lb. delbrueckii subsp. lactis and E. faecium exhibited a fast acidifying ability. Most lactobacilli revealed higher aminopeptidase and autolytic activity when compared with other strains. Twenty-seven percent of tested strains appeared to have antimicrobial activity and the highest inhibitory activity was observed among enterococci (13% of 188 strains). Exopolysaccharides (capsule) were detected in 4.3% of the lactobacilli. Most strains were able to produce a high yield of biomass after growth, showed a good biomass separation and were not affected by lyophilisation treatment. Strains which showed outstanding characteristics were screened for their flavour-forming abilities in milk cultures. Ninety-one strains, 7 Lactococcus, 52 Lactobacillus and 32 Enterococcus, were selected for an application in Ras cheese according to their production and technological criteria: salt tolerance, ability to grow at 40-45°C, acid production, proteolytic activity, flavour and bacteriocin production. These strains are currently being tested in pilot-scale cheese trials to improve Egyptian Ras cheese. © INRA, EDP Sciences, 2006.