Antimicrobials control L. monocytogenes on commercial frankfurters during storage.

L. monocytogenes contamination of ready-to-eat meat products, even after a lethality treatment, is of major concern to the meat processing industry. For this reason, scientists at Colorado State University investigated the antilisterial effect of antimicrobial treatments.

The treatments were applied as dipping solutions on commercial frankfurters inoculated with cultures of L. monocytogenes of different origins and stored at 10 C. The investigators found that adding antimicrobials in the formulation of frankfurters and following that up by dipping them in antimicrobial solutions was very effective in controlling the growth of L. monocytogenes during product storage.

Commercial frankfurters, formulated with or without antimicrobials, were inoculated with a 10-strain mixture of L. monocytogenes. The inocula evaluated included: cells grown in tryptic soy broth plus 0.6% yeast extract (TSBYE); cells grown planktonically in a smoked sausage purge at 15 C for 7 days; and cells attached to stainless steel coupons immersed into a smoked sausage purge at 15 C for 7 days.

Researchers dipped inoculated frankfurters for 2 minutes into solutions of acetic acid (2.5%), lactic acid (2.5%), potassium benzoate (5%) or Nisaplin (0.5%), either singly or sequentially. This was followed by vacuum packaging and storing the product at 10 C for 48 days. The growth of L. monocytogenes on undipped frankfurters formulated without antimicrobials exceeded 7.3 log CFU per [cm.sup.2] in 12 days. In products containing antimicrobials, bacterial growth was inhibited for up to 12 days, depending on the inoculum type used. Bacterial growth reached more than 6.3 log CFU per [cm.sup.2] at 48 days.

Dipping resulted in initial reductions of L. monocytogenes from 1.0 to more than 3.9 log CFU per [cm.sup.2]. Two of the most effective treatments-acetic acid applied singly or sequentially with Nisaplin-in products formulated without antimicrobials inhibited growth for at least 12 days. Growth in products formulated with antimicrobials was inhibited by all dipping treatments throughout the storage period, except for potassium benzoate or Nisaplin applied singly.

Further information. John Sofos, Department of Animal Sciences, Colorado State University, 1171 Campus Delivery, Fort Collins, CO 80523; phone: [phone]; email: [e-mail] <mailto:[e-mail]>.