Growth suppression of Listeria monocytogenes in a meat product.

Bologna-type sausages were manufactured using standard industry processes and four different formulations: (a) standard commercial formulation (control), (b) with 2% sodium lactate, (c) with 2% lactate and 0.25% glucono-delta-lactone (GDL), (d) with 2% lactate and 0.5% GDL. The sliced sausages were inoculated with a mixture of L. monocytogenes serotype 1 and 4 (approximately 100 cfu/g). The samples were vacuum-packaged and stored at 5 degrees C and 10 degrees C for 35 days. Rapid growth of L. monocytogenes was observed in control samples stored at 5 degrees C and in control samples and lactate treated samples (without GDL) stored at 10 degrees C. In sausages containing GDL (both levels) growth did not occur within 35 days at either 5 degrees C or 10 degrees C. Thus the presence of GDL at low level seemed sufficient to prevent growth of L. monocytogenes, although pH in the product was as high as 6.3. In samples with 2% lactate and without GDL, growth was suppressed for 28 days at 5 degrees C. Results indicate that it is possible to suppress growth of L. monocytogenes in chilled cooked meat products by using suitable amounts of sodium lactate combined with lowering of pH. However, when using GDL as a pH lowering agent, off-flavours may be registered by some individuals at high levels of GDL.