Fate of acid-adapted and non-adapted Escherichia coli O157:H7 inoculated post-drying on beef jerky treated with marinades before drying

Abstract

The objective of the present study was to investigate survival of acid-adapted and non-adapted E. coli O157:H7 inoculated after drying on beef jerky that was treated with marinades before drying. Beef slices were not marinated before drying (control—C), or subjected to the following marinades (24 h, 4°C) prior to drying at 60°C for 10 h: (1) traditional marinade (TM), (2) double the amount of TM modified with added 1.2% sodium lactate, 9% acetic acid, and 68% soy sauce with 5% ethanol) (MM), (3) dipping into 5% acetic acid followed by TM (AATM), and (4) dipping into 1% Tween 20 and then into 5% acetic acid followed by the TM (TWTM). Dried slices were inoculated with acid-adapted or non-adapted E. coli O157:H7 ( c. 6.2 log cfu cm −2) prior to aerobic storage at 25°C for 60 days. Survivors were determined using tryptic soy agar with 0.1% pyruvate, modified eosin methlylene blue agar, and sorbitol MacConkey agar. Results indicated that bacterial populations decreased during storage in the order of predrying marinade treatments TWTM⩾AATM>MM>C⩾TM. Populations decreased faster on jerky inoculated with acid-adapted cultures than with non-adapted cultures in all treatments. A 5.0 log reduction in bacterial counts was achieved within 7 days (TWTM and AATM) or never achieved during the 60 days storage period (C, TM). The earliest elimination (enrichment negative) of the pathogen occurred by 28 days (TWTM, ATTM and MM) in products inoculated with acid-adapted cultures and by 42 days (TWTM and AATM) in products inoculated with non-adapted cultures. It is concluded that under the conditions of this study, modified marinades and low water activity provide antimicrobial effects against possible post-processing contamination of beef jerky with E. coli O157:H7. Acid adaptation of cultures enhanced their inactivation during storage.