Nisin sensitivity of cooked meat products spoilage bacteria

HERMAN, CRISTIAN;PALAVECINO PRPICH, NOELIA; CASTRO, MARCELA P.; CAYRÉ, MARÍA E.; GARRO, OSCAR A.

Rosario, Pcia. de Santa Fé

Congreso; V Congreso Argentino de Microbiología General; 2008

SAMIGE

Lactic acid bacteria (LAB) were identified as the major spoilage population of vacuum-packaged emulsion-type sausages and other processed meats stored at refrigeration temperatures. Brochothrix thermosphacta is also found to be a numerical significant component of the microflora of meat and meat products stored under these conditions. LAB and B. thermosphacta significantly influence the quality of meat and meat products, both being associated with spoilage in these products. Under anaerobic conditions LAB may cause souring, slimy, swelling of the pack and/or greening, while B. thermosphacta produce mainly lactic acid, ethanol and only small amounts of short chain fatty acids causing off-odours. One approach to extending the storage and shelf life of meat products is to introduce antimicrobials, preferably naturally occurring antimicrobials, to the products. Nisin, produced by Lactococcus lactis subsp.lactis, is a small, heat-stable protein, classified as a lantibiotic. Its spectrum of activity is limited and includes many gram-positive bacteria and their spores. Nisin is generally recognized as safe (GRAS) for use as a food additive in many countries. The aim of this work was to evaluate nisin sensitivity against spoilage microflora associated to cooked meat products manufactured in the province of Chaco. Vienna-type cooked sausage, “mortadela”, “Cracovia” and cooked ring sausage were prepared in local meat processing plants by traditional techniques. The products were vaccum-packaged in low oxygen permeability films and stored at 8ºC until signs of deterioration were observed. From these products several strains were isolated, selected and purified followed by characterization using Gram stain, cell morphology and catalase and oxidase reaction. Agar well difussion assay was used to determine microorganism sensitivity towards nisin. Minimun inhibitory concentration (MIC) of nisin for each strain was performed by the critical dilution method; being 78 ppm the lowest concentration tested. Plates were incubated in the optimal conditions for each isolate and then inhibition zones were examined. Thirty-seven strains were selected. According to the characterization, four of them were Brochothix spp. and the rest corresponded to LAB. The MIC could only be determined on seven LAB isolates since the rest of them showed sensitivity even at the lowest concentration of nisin. In further assay, dilution series will be extended in order to determine the MIC of the total isolates. The high sensitivity to nisin displayed by all the strains isolated from deteriorated cooked meat products suggests its promising use as a biopreservative in the local meat industry. In the future, the combined utilization of nisin with lysozyme and EDTA will also be investigated in order to achieve a broader spectrum of inhibition which comprises Gram (-) bacteria.