Influence of inoculum level and acidic marination on inactivation of Escherichia coli O157:H7 during drying and storage of beef jerky.

Abstract

The objective of this study was to evaluate the influence of Escherichia coli O157:H7 inoculum level (4 [L] and 7 [H] log cfu/cm(2)) on its inactivation during drying and storage of beef jerky slices (8.7 x 4.0 x 0.6 cm). Beef jerky slices at each inoculum level were untreated (C), exposed to a traditional marinade (M), or exposed to a 5% acetic acid solution followed by traditional marination (AM). Surviving bacterial populations were determined during 10h of drying (60 degrees C) and 60days of aerobic storage (25 degrees C) using tryptic soy agar supplemented with 0.1% pyruvate (TSAP), sorbitol MacConkey (SMAC) agar, and modified eosin methylene blue (MEMB) agar, Irrespective of recovery Culture media and inoculation level, the AM treatment decreased (P < 0.05) bacterial populations more (P < 0.05) than the C or M treatments during the 10 h of drying. The death rate (log cfu/h) in AM-treated samples was higher during the first 4 h of drying (first death phase) for H (0.9) than L (0.5-0.6); however, death rates in samples of C and M treatments were 0.7 and 0.6-0.7 at H and 0.7-0.8 and 0.7-0.8 at L, respectively. The results suggest that the acetic acid treatment may have sensitized the cells at the high inoculum level causing inactivation by drying, thus enhancing destruction of higher inoculation levels. (c) 2004 Elsevier Ltd. All rights reserved.