Influence of marinades on survival during storage of acid-adapted and nonadapted Listeria monocytogenes inoculated post-drying on beef jerky

The objective of the present study was to investigate the survival of acid-adapted and nonadapted Listeria monocytogenes inoculated post-drying on dried beef slices (beef jerky), which were treated (24 h, 4 °C) with the following marinades before drying at 60 °C for 10 h: (1) control (C), (2) traditional marinade (TM), (3) modified marinade; double the amount of TM with added 1.2% sodium lactate, 9% acetic acid, and 68% soy sauce with 5% ethanol (MM), (4) dipping into 5% acetic acid and then TM (AATM), and (5) dipping into 1% Tween 20 and then into 5% acetic acid followed by the TM (TWTM). Dried meat slices were inoculated with acid-adapted or nonadapted L. monocytogenes (ca. 5.7 log CFU/cm2) prior to aerobic storage at 25 °C for 60 days. Survivors were determined using tryptic soy agar with 0.1% pyruvate (TSAP) and PALCAM agar. Results showed that surviving bacterial populations on TWTM, AATM, and MM treatments were significantly (P<0.05) lower than those surviving on C and TM until 42 days of storage. By the end of 60 days of storage, bacterial populations in all treatments were not different regardless of acid adaptation or recovery media, except for treatment C inoculated with nonadapted cultures, which had significantly higher TSAP counts than other treatments. There was no significant (P > or = 0.05) difference in survival of previously acid-adapted and nonadapted bacterial populations in samples of TWTM, AATM, and MM treatments. However, bacterial populations that were nonadapted were significantly higher than those that were acid-adapted on products of C and TM treatments on days 60 and 24, respectively. The earliest complete elimination (enrichment negative) of the pathogen occurred by day 28 (AATM) in products inoculated with acid-adapted cultures and by day 42 (TWTM and AATM) in products inoculated with nonadapted cultures. These results indicate that use of modified marinades in jerky processing and low water activity provided antimicrobial effects against possible post-processing contamination with L. monocytogenes.