Organic Acids Production and Antagonistic Effect of Some Strains of Probiotics

Abstract

Organic acids production and antimicrobial activities of Lactobacillus acidophilus KF724889, Lactobacillus casei KF724890 and Streptococcus thermophilus KF724886, KF724887 and KF724888 strains, which isolated from dairy products as probiotics were screened. Eleven organic acids were detected in the different LAB filtrates, acetic, ascorbic, citric, formic, oxalic, malic, maleic, lactic, propionic, butyric and succinic acids. lactic and acetic acids were the major acids produced by the five strains. Lactobacillus in general and L. acidophilus in especial were the most active in acids production. Both L. acidophilus and L. casei produced the highest quantity of lactic acid, being 3257.4 and 2447.75 mg/100 ml, respectively, while Str. thermophilus strains KF724886, KF724887 and KF724888 produced 1613.36, 1964.52 and 2031.131 mg/100ml, respectively. Formic acid did not produce by Str. thermophilus KF724886. Supernatants obtained from the tested bacteria exhibited varying degrees of inhibitory effect against indicators pathogenic bacteria and yeast. All the tested bacteria have antagonistic effect against Staphylococcus aureus, Pseudomonas aeruginosa and Protus vulgaris. Among the isolates, L. acidophilus was the most effective strain for inhibiting pathogens growth with strong inhibitory effect against P. aeruginosa, L. monocytogenes and Candida albicans. Only L. acidophilus and Str. thermophilus KF724888 caused inhibitory effect against Bacillus cereus, L. monocytogenes and C. albicans. L. casei, Str. thermophilus KF724886 and Str. thermophilus KF724887 failed in inhibiting growth of E. coli, B. cereus, L. monocytogenes and C. albicans. L. acidophilus inhibited growth of E. coli, while Str. thermophilus KF724888 failed. The results showed that all cell free supernatants (CFSs) of LAB cultures have ability to inhibit all the tested foodcontaminating fungi. Based on dry weight measurements of fungal biomass, CFSs of L. acidophilus showed high antifungal activity against the tested fungi. CFSs of Str. thermophilus KF724887 strain showed strong inhibition percentages against growth of A. niger, T. harzianum, P. chrysogenum and A. pullulans (56.63, 54.84, 52.92 and 38.88%, respectively). The study revealed that lactic acid bacteria isolated from Egyptian fermented milk, are capable of producing organic acids and antimicrobial substances which have antagonistic effect on pathogenic organisms, thus, may be promising sources of preservative that may in future be applied to food.