Destruction of acid- and non-adapted Listeria monocytogenes during drying and storage of beef jerky

Presence of Listeria monocytogenes in ready-to-eat meat products is not desired and strictly regulated in the US. Inactivation of acid- and non-adapted L. monocytogenes inoculated on beef slices was studied during drying and storage of jerky formulated with modified marinades. The inoculated (five-strain composite, c. 6.2 log cfu cm(-2)) slices were subjected to marinades (4degreesC 24 h) prior to drying (60degreesC for 10 h) and aerobic storage (25degreesC for 60 days). The predrying marinade treatments tested were, first, no treatment, control (C); second traditional marinade (TM); third double amount of TM modified with 1.2% sodium lactate, 9% acetic acid and 68% soy sauce containing 5% ethanol (MM); fourth, dipping into 5% acetic acid for 10 min and then applying the TM (AATM); and fifth dipping into 1 % Tween 20 for 15 min and then into 5% acetic acid for 10 min followed by the TM (TWTV). Bacterial survivors on beef slices were determined during drying and storage using tryptic soy agar with 0.1 % pyruvate (TSAP), and PALCAM agar. Results indicated that drying reduced bacterial populations in the order of pre-drying treatments TWTV (5.9-6.3 log ctu cm(-2) in 10h) greater than or equal toAATMgreater than or equal toMM>TWgreater than or equal toC (3.8-4.6 log cfu cm(-2) in 10h). No significant (Pgreater than or equal to0.05) difference was found in inactivation of acid-adapted and non-adapted inocula within individual treatments. Bacterial populations dropped below the detection limit (-0.4 log cfu cm(-2)) as early as 4h during drying or remained detectable even after 60 days of storage depending on acid-adaptation, predrying treatment, and agar media. These results indicated that acid-adaptation may not increase resistance to microbial hurdles involved in jerky processing and that use of modified marinades may improve the effectiveness of drying in inactivating L. monocytogenes. (C) 2002 Elsevier Science Ltd. All rights reserved.