Antimicrobial Effects of Bacteriocins Produced by Lactic Acid Bacteria Against Listeria on Cantaloupe (Cucumis Melo) Surface

Bacteriocins produced by lactic acid bacteria (LAB) are considered generally regarded as safe (GRAS) and may reduce pathogenic loads on the cantaloupe surface. The efficacy of these bacteriocins on reducing the pathogenic loads of Listeria was evaluated. A Cantaloupe’s netted surface provides for attachment of pathogens from soil and water, which then contaminate the surface of the cantaloupe. Non-pathogenic bacteria, Listeria innocua B-33016 was used as a surrogate for L. monocytogenes. Two bacteriocins, (1) nisin and (2) pediocin, were produced from Lactococcus lactis subsp. lactis ATCC 11454 and Pediococcus acidilactici RS2-10, respectively. The bacteriocins were partially purified and freeze-dried. The minimal inhibitory concentration (MIC) and antimicrobial activity of the freeze-dried bacteriocin powders to inhibit L. innocua was evaluated for each powder. L. innocua was inoculated on the surface of cantaloupes at a concentration of 4.69 ± 0.37 log CFU/cm2 and then the cantaloupes were kept for 1 hour at 23 °C. Then the cantaloupes were separately dipped in nisin (NBP), pediocin (PBP), or a combination of nisin and pediocin (NPBP) solutions. Cantaloupes dipped in water and cantaloupes not dipped in either water or bacteriocin solutions were used as controls. L. innocua counts, Aerobic (APC), yeast and mold counts, color, and firmness of the cantaloupes were determined. Data from triplicate experiments were statistically analyzed (p≤0.05). The MIC of NBP and PBP were 10 µg/mL and the antimicrobial activity of the powders was 3.34x107 IU/g and 1.01x108 UI/g, respectively on L. innocua. Application of NBP, PBP, or PNBP significantly reduced L. innocua on the cantaloupes by approximately 1.29, 1.09, and 1.68 log CFU/cm2, respectively. Compared to the controls, bacteriocin applications significantly reduced APC, yeast and mold counts regardless of bacteriocin type. Bacteriocin application did not affect the color or firmness of the cantaloupes. This study demonstrated that bacteriocin could reduce Listeria loads on the surface of cantaloupes and PNBP was more effective in reducing Listeria than NBP and PBP alone. The PBP, NBP, and PNBP may be of interest to fresh produce companies and the food industry in general