Lactobacillus plantarum F1 and L. brevis OG1 isolated from Nigerian fermented food products, produced bacteriocins that had broad spectrum of inhibition against both pathogenic, food spoilage organisms and various lactic acid bacteria. The test organisms exhibited activities of 6400 and 3200 AU/ml respectively against Escherichia coliNCTC10418 and Enterococcus faecalis EF1, but did not inhibit Candida albicansATCC10231 and Klebsiella sp. UCH15. Comparison of the antimicrobial spectra and characterization of the two bacteriocins were not identical. Bacteriocin produced by L. brevis OG1 was the most heat stable at 121oC for 60 min, while that of L. plantarumF1 was stable at 121oC for 10 min. The bacteriocins produced by the test isolates maintained full stability after storage for 60 days at – 200C; partial stability after storage for 120 days at 40C; while activity was not detected after storage for 80 to 120 days at 370C. Bacteriocin produced by L. brevis OG1 was stable at pH range of 2.0 to 8.0 while, that of L. plantarum F1 was found to be stable at pH 2.0 to 6.0. Their active principle was proteinaceous in nature since the bacteriocins were inactivated by proteolytic enzymes, but not by other non–proteolytic enzymes. mitomycin C and uv light did not affect the activity of the bacteriocins, while chloroform extraction completely destroyed their activity. Exposure to surfactant resulted in an increase in the bacteriocin titre, except Nonidet P-40, which led to total loss of bacteriocin activity. The bacteriocins were able to pass through cellulose membranes with 100,000 KDa and 1,000,000 KDa but could not pass through one with a 10,000 KDa and 1,000 KDa molecular weight cut off. The paper concluded that the ability of bacteriocins produced by the test isolates in inhibiting a wide-range of bacteria, is of potential interest for food safety and may have future applications as food preservative.
Key words: Bacteriocins, lactic acid bacteria, indicator organisms, fermented foods, antagonistic activity.
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