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

The objective of this study was to evaluate the influence of Escherichia coli O157:H7 inoculum level (4 [L] and 7 [H] log cfu/cm2) on its inactivation during drying and storage of beef jerky slices (8.7×4.0×0.6 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 10 h of drying (60 °C) and 60 days of aerobic storage (25 °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.