Lactic acid bacteria (LAB) responsible for spontaneous fermentation of cucumber were isolated and their antimicrobial producing potentials were screened against 10 indicator strains. 65% of the isolated LAB produced antimicrobial activities against at least two indicator strains. The indicator strains used were: Escherichia coli, Bacillus licheniformis, B. cereus, Proteus species, Staphylococcus aureus, Salmonella species, Pseudomonas flourescence, P. aeruginosa, Serratia species and Pediococcus acidilactici. Of the 42 antimicrobial producing isolates characterized, 16, 12, 6 and 8 were identified as Lactobacillus plantarum, L. fermentum, L. acidophilus and Leuconostoc mesenteroides, respectively. Highest lactic acid producers DW7, DT6, DH13 and DF12 were selected for further investigations and were identified as L. plantarum. None of the selected L. plantarum isolates had antagonistic activity against S. aureus, Salmolnella species and P. acidilactici. The effect of pH and temperature on the antimicrobial activity of selected isolates showed that pH 5.5 and temperature 30°C were the optimum pH and temperature respectively. Thus, the selected L. plantarum isolates are good producers of antimicrobial compounds and could be suitable for application in food industry in preservation of vegetables so as to increase their shelf life.

Objective: To determine the best starchy food substrate for the fermentative production of lactic acid. Methodology and Results: Five starchy-based food substrates (maize ogi, sorghum ogi, millet ogi, mashed cassava for gari production and steeped cassava for fufu production) were prepared fresh and allowed to ferment spontaneously for a period of 7days during which samples of the substrates were subjected to microbiological and chemical analysis. Four growth media were used for the isolation of the different common group of organisms implicated. Yeasts and Molds were identified as Saccharomyces cerevisiae, Candida sp., Aspergillus niger, Aspergillus flavus and Penicillium sp. The bacteria were Lactobacillus plantarum, Lactobacillus casie, Lactobacillus fermentum, Lactobacillus lactis, Klebisella pnemoniae, Escherichia coli, Flavobacterium sp., Proteus vulgaris. The pH decreased with increase in fermentation time, and it ranged from 3-6 while the total titratable acidity increased within the first 2-3days in cereal-based foods and within the first 4-5days in cassava based food substrates, followed by a gradual decrease. Though the lactic acid content fluctuates during the fermentation period, statistical analysis shows that fermentation time has significant effect (p<0.05) on the quantity of lactic acid produced. The two methods (total titratable acidity and spectrophotometric) used to measure the lactic acid content gave similar result of increase within the first 2-3days with an intermittent decrease and increase at subsequent days. Statistical analysis revealed that both the method and substrate used has significant effect (p<0.05) on the quantity of lactic acid content produced. Conclusion and application of study: from this study, the steeped cassava produced the maximum lactic acid on the 4 th day of fermentation by the two methods used. The results of this study revealed that lactic acid could be produced naturally from steeped cassava. Therefore, the best processing conditions and other optimization parameters should be investigated. Application of results: The study shows the possibility of Lactic acid biosynthesis using cassava, a low-cost and readily available substrate as source for laboratory/ small scale and eventually large-scale production.

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