Technological properties and antagonistic effect of lactic acid bacteria isolated from fermented goat milk flavoured with juniper leaves – a product from the southwest region of Algeria – against some microbial contaminants
Keywords:Lactic acid bacteria, microbial contaminants, antagonistic effect, goat milk, fermentation, Phoenician juniper leaves
AbstractLactic acid bacteria (LAB), as microorganisms that are naturally present in milk and dairy products, have interesting technological and antimicrobial properties. This study focussed on the antagonistic effect of LAB isolated from fermented goat milk naturally flavoured with Phoenician juniper leaves against some microbial contaminants, and some reference strains. First, microbial contaminants were isolated from dairy and meat products using selective media according to national standards. Second, a study of the technological properties of lactic strains isolated from goat milk flavoured with Phoenician juniper leaves was carried out, including an analysis of any antibacterial effects against microbial contaminants. This was established through spot tests on agar. Antifungal activity was established through mycelial radial growth on agar, and the evaluation of biomass on broth culture. Eleven microbial contaminants were isolated and identified: seven bacterial species – Enterobacter sp (1) and (2), Salmonella sp, Pseudomonas sp, Staphylococcus sp, S. aureus, Enterococcus sp (fecal streptococci); four fungal species – Saccharomyces sp, Candida albicans, Penicillium sp, and Aspergillus niger. Antibiotic susceptibility results showed that Enterobacter sp (1) and (2) and Salmonella sp strains were resistant to several antibiotics, namely ampicillin, amoxicillin/clavulanic acid, cefoxitin, and imipenem. Pseudomonas sp was resistant to imipenem, fosfomycin and amikacin. Staphylococcus spp and S. aureus strains were resistant to penicillin, oxacillin, and fosfomycin. Enterococcus sp was resistant to ampicillin and tetracycline. However, 13 isolates of Streptococcus were isolated from fermented and flavoured goat milk, each with different physiological and technological characteristics. Five strains (38.5%) showed good acidifying power and 13 strains (100%) revealed good proteolytic activity. High titratable acidity of 5.13 g/L of lactic acid was recorded for the thermophilic Streptococcus sp strain (St2). Although all LAB of streptococci species were resistant to penicillin and cotrimoxazole, they were susceptible to the majority of the tested antibiotics, and are therefore considered safe for use as probiotics. The antimicrobial effect results show that the isolated LAB strains have an antagonistic effect by inhibiting the growth of contaminating strains. This activity was important against the tested yeasts Saccharomyces sp, and Candida albicans. A greater antifungal action against Penicillium sp was also observed compared to the species A. niger, with a reduced rate of the fungal biomass which can go up to 90%. Regarding antibacterial action, Gram-positive bacterial contaminants, namely Enterococcus sp and the reference strain Bacillus cereus ATCC 14579 were the most susceptible among the tested bacteria, with zones of inhibition ranging from 14 mm to 22 mm. A medium to weak action was revealed against Enterobacter sp (1) and (2), Pseudomonas sp, Salmonella sp, and both isolated and reference S. aureus species. These results, obtained from a study of traditional practices of great indigenous wealth in the southwest regions of Algeria, constitute a perspective and platform for future investigation on the characteristics of microbial microflora in dairy products by helping in the selection of lactic strains of technological interest.