Assessment of the antimicrobial activity of lactic acid bacteria isolated from two fermented maize products - ogi and kunnu-zaki

The lactic acid bacteria (LAB) used in this study were isolated from two traditional fermented maize products-ogi and kunnu-zaki. The antimicrobial activities of the isolated LAB against some indicator organisms (Staphylococcus aureus, Escherichia coli, Klebsiella pneumonia, Proteus mirabilis and Bacillus cereus) was investigated. The LAB population in the ogi samples ranged from 5.39 log cfu/g to 6.40 log cfu/g while that of kunnu-zaki ranged from 6.11 log cfu/g to 6.70 log cfu/g. The lactic acid bacteria isolated were identified as Lactobacillus plantarum, L. fermentum, L. lactis, L. acidophilus, L. mesenteroides, L. casei, and Streptococcus thermophilus. Cell free supernatant of the LAB was able to inhibit the growth of the indicator organism used. The largest zone of inhibition was 11 mm produced by L. plantarum against Klebsiella pnuemoniae while the least zone of inhibition was 3 mm produced by L. acidophilus against E. coli. The LAB tested also produced various antimicrobial compounds such as lactic acid, diacetyl and hydrogen peroxide and quantitative estimation of these antimicrobial compounds was carried out. The highest yield of lactic acid was 2.18 g/L produced by S. thermophilus, highest yield of diacetyl was 2.5 g/L produced by L. plantarum while the highest yield of hydrogen peroxide was 0.006 g/L produced by L. plantarum.