ABSTRACT

Lactic acid bacteria have significant potential for use in food processing and especially dairy products because they are safe and naturally dominate the micro flora of many foods during storage. The aim of this study was to isolate some Lactic Acid Bacteria from raw milk and characterize them biotechnologically. Seven lactic acid bacteria isolated from cow and goat milk samples were studied for their technological properties. They were identified as Lacto bacillus plantarurn, Lacto bacillus casei, Lactobacillus brevis, and Streptococcus therinophillus. In raw goat milk, the population of LAB was in the range of 6.9 x 106cfu/ml to 1 .02 x 107cfu/hul while for the cow the LAB population ranged between 7.4 x 106cfu/ml to 1 .03 x 106cfu/rnl. The pH of the MRS broth medium inoculated with the respective LAB isolates stood between 5.70 to 5.90 after l2hrs of incubation. Drastic reduction in the pH values were observed with incubation time. The lowest pH value was recorded for isolate C2 which had 3.10 after 36hrs. The other isolates followed a similar trend in drop of pH. The tested isolates exhibited clear zones of inhibition on the indicator strains. Among these isolates, the widest spectrum of antimicrobial activity appeared to be displayed by isolates C2and G3. Cell free supernatants from Isolate C2 (Lactobacillus planiarum) gave zones of inhibition 16.0mm and 13.0mm against Staphylococcus aureus and Pseudomonas aeruginosa. Also, isolate G3 (Streptococcus species) showed remarkable antagonism against E. coli and S. aureus with inhibition zone sizes of 14.0mm and 13.0mm respectively. The amount of lactic acid produced by the respective isolates ranged within 2.10-3.10 mg/I in which L. plantarurn had the highest at l2hrs of incubation. The 'S highest lactic acid production at 24hrs (3.70mg/I) was from L. plantarum while the lowest production at 24hrs (2.70mg/i) was by L. brevis. Similarly, the highest concentration of 0.34mg/I (table 4.3) was recorded for Lactobacillus plantarurn. The range of H202produced by the isolates after incubation for 12hrs and 24hrs respectively were 0.o9mg/l to 0.24mg/i and 0.1 4mg/I to 0.29mg/l. These isolated strains can positively have impact on use of starter cultures for traditional fermented foods, with a view to improving the shelf life.