Screening of a food-grade antimicrobial from Lactococcus species of raw milk origin, and optimization of the antimicrobial activity

Document Type


Publication Date



American Dairy Science Association


Journal of Dairy Science




Suppl. 1






Lactococcus lactis ssp. lactis, nisin, optimization


Antimicrobials produced by Lactococcus species of milk origin are valu- able as natural inhibitors against food spoilage and pathogenic micro- organisms. An example is nisin, which has diverse food preservation applications. This study was performed to isolate and identify Lactococ- cus species from raw milk having antimicrobial activity against selected food spoilage organisms, with the potential to optimize conditions for improved antimicrobial production. During the initial screening, lactic acid bacteria were isolated on MRS agar from 47 raw milk samples from the University dairy farm. Based on colony morphologies on the selec-tive medium, Gram staining, and catalase test, 5 isolates were selected, and screened for antimicrobial activity using agar well assay technique. All the isolates were observed to secrete antimicrobial compounds, active against a test strains Micrococcus luteus (ATCC 10240) and Lac- tococcus lactis ssp. cremoris (ATCC 19257). The diameter of clear zone around the well of 5 isolates corresponded to an antimicrobial activity of 48.90, 265.41, 213.15, 371.95, and 505.00 IU/mL respectively. Two larger isolates, N40615 and N50615 (P < 0.05), were chosen for further experiments but N50615 produced less antimicrobial activity againstLactococcus lactis ssp. cremoris (ATCC 19257). As a result, N40615 was selected for further studies. On the evaluations for identification and characterization, the inhibitory substance was not identified to be either hydrogen peroxide or bacteriophage. As the inhibitory activity was inactivated by α-chymotrypsin, proteinase, and trypsin, it was concluded that the isolate produced nisin-like antimicrobial activity. N40615 in autoclaved skim milk medium heat treated at 85°C for 15 min supplemented with 0.50% peptone, 0.25% yeast extract, and 0.3% dipotassium phosphate (W/W), without pH control, had 1,571.0 IU mL−1 of antimicrobial activity, and the one with pH control, had 3,896.7 IU/mL of antimicrobial activity (P < 0.05). This nisin-like bacteriocin is inhibitory to salad dressing spoilage organisms such as Lactobacillus brevis (ATCC 367), Lactobacillus buchneri (ATCC11305), and Lactoba- cillus plantarum (ATCC 8014). In conclusion, the results demonstrated that the antimicrobial activity of the isolated culture N40615 from raw milk was comparable to that of nisin in Nisaplin.

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