Abstract
Many lactic acid bacteria (LAB) were isolated from “Shermout”, a popular Sudanese fermented beef product intended for long storage. An isolate that demonstrated significant antibacterial activity was identified as Lactobacillus plantarum PM4 based on phenotypic, physiological and biochemical characteristics and carbohydrate utilization patterns. The inhibitory activity of the partially purified bacteriocin was completely arrested by the proteolytic enzymes proteinase-k and pepsin but not by α-amylase, asserting its proteinaceous nature. The activity was not due to H2O2 as similar inhibition was obtained by cell-free supernatant (CFS) produced under anaerobic conditions. The bacteriocin showed a molecular weight in the range of 3 - 5 kDa and had a bactericidal mode of action. No significant reduction in activity was observed on heating to 60℃ for 60 min, but activity was lost on heating to 100℃ or autoclaving. Highest inhibitory activity was at pH 5.5 and there was appreciable reduction in activity at pH 3, 7 or 9. There was no drop in activity at –80℃ or –20℃ up to four weeks of storage. However, at 4℃ and 35℃, a gradual decline in activity was observed. Lb. plantarum PM4 exhibited bactericidal activity against Staphylococcus aureus, Bacillus subtilis, Enterococcus faecalis, Escherichia coli ATCC25922, Klebsiella pneumoniae and Proteus vulgaris. Bacteriocin production generally coincided with the phase of maximum growth and the best combination for maximum production of inhibitory activity was at pH 5.5 for 48 h whether incubated at 25℃, 30℃ or 37℃. Lb. plantarum PM4 showed promise as a starter culture in the fermentation of preserved meat products.
Highlights
Many lactic acid bacteria (LAB) were isolated from “Shermout”, a popular Sudanese fermented beef product intended for long storage
Lactic acid bacteria (LAB) is a group of Gram positive facultative anaerobic bacteria that are able to produce antagonistic molecules in their growth medium that can be used as antimicrobials and preservatives
LAB is used in food biopreservation because they are safe for human consumption enjoying the status of GRAS (Generally Recognized as Safe) and are the prevalent indigenous microflora in many foods
Summary
Lactic acid bacteria (LAB) is a group of Gram positive facultative anaerobic bacteria that are able to produce antagonistic molecules in their growth medium that can be used as antimicrobials and preservatives. These antagonistic properties of LAB are allied to their safe history of use in traditional fermented food products that make them very attractive as biopreservatives that can replace or allow reduction of chemical additives [1]. The antimicrobial activity of this group of natural substances against foodborne pathogens, as well as spoilage bacteria, has raised considerable interest for their application in food preservation [2] [9] [10] [11]
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