Effect of sodium lactate, sodium nitrite, pH and temperature on growth of Listeria monocytogenes

Standard Bologna-type sausages were manufactured using six different formulations: (a) standard with 60ppm nitrite, (b) standard with 150ppm nitrite, (c) standard with 60ppm nitrite and 2% lactate, (d) standard with 150ppm nitrite and 2% lactate, (e) standard with 60ppm nitrite and 3% lactate, (f) standard with 150ppm nitrite and 3% lactate. PH was kept at 6,3 for all formulations. The sliced sausages were inoculated with a strain of Listeria monocytogenes (L.m.) serotype 4 (700 cfu/g). The samples were vacuum-packaged and stored at 4 degreesC and 8 degreesC for 35 days. Rapid growth of L.m. was observed in formulations a and b, at 4 degreesC and 8 degreesC. In formulation c after 35 days of storage the level of L.m. was equal to the inoculation level at 4 degreesC. However at 8 degreesC growth started after 2 weeks storage and reached a level of 1 million L.m. per gram after 35 days. In formulation d, e and f no growth was observed after 35 days either at 4 degreesC or 8 degreesC. However, when using 3% lactate, off-flavours were registered by a trained taste panel. It can be concluded that it is possible to prevent growth of L.m. in chilled meat products at pH 6.3 for 35 days using suitable amounts of sodium lactate and sodium nitrite. However the concentration of lactate should not exceed 2% for quality reasons.