Post-processing Pasteurization of Packaged Frankfurters for Control of Listeria monocytogenes

Contamination of processed frankfurters with Listeria monocytogenes occurs between the removal of the casing and the packaging steps. Every year, this contamination causes numerous recalls and several cases of listeriosis. The purpose of this study was to combine a lactic acid treatment and the application of post-packaging steam to reduce L. monocytogenes populations on vacuum packaged, refrigerated mixed meat frankfurters. Changes in color and texture of frankfurters after treatment were also monitored.

In Part I of the study, frankfurters were inoculated with a five-strain mixture of L. monocytogenes (log 7 CFU/frankfurter). After 24 hours, the surface of the frankfurter was treated with a lactic acid (0, 0.5 and 1.5%) dip for 10 seconds. The frankfurters were then vacuum packaged and treated with 85±5°C steam for 0, 1, 2 or 4 minutes. L. monocytogenes was enumerated on modified oxford agar (MOX) and tryptose phosphate agar (TPA). Populations were compared to those on untreated frankfurters. Results of this study indicate that lactic acid alone had no significant effect on bacterial populations (p>0.05). Steam treatment significantly decreased bacterial populations (p<0.05), but also increased the hardness and toughness of frankfurters.

For the second part of the study the study (Part II), the length of the lactic acid treatment was increased to three minutes and used only at a concentration of 1.5% and 0% as control. Steam treatment times were reduced to 0, 0.5, 1, and 1.5 minutes. Lactic acid reduced L. monocytogenes populations (p<0.0001), but this longer contact (3 min) with lactic acid also affected color and texture of frankfurters (p<0.05). Steam treatment also decreased bacterial populations (p<0.05). These results demonstrate that a combination of steam and lactic acid can be used to decrease populations of L. monocytogenes on vacuum packaged frankfurters and could be of use in frankfurtermanufacturing.