Purpose: This study evaluated efficiency of a mixed STEC inoculum to attach to raw beef carcass (lean or fat), and efficacy of 4.5% lactic acid (LA) or water (W) spray to reduce STEC populations, under four scenarios: (A) pre-rigor surface STEC inoculated (ca. 4 log CFU/cm2), 30-min ambient temperature attachment, spray with LA or W; (B) pre-rigor inoculated, 24-h chilled attachment, spray; (C) tissue chilled 24 h, inoculated, 30-min attachment, spray; and (D) tissue chilled 24 h, rewarmed to 37°C, inoculated, 30-min attachment, spray.
Methods: Lean and fat tissues (230 cm2) were collected from two fed cattle at harvest and assigned to the four scenarios, followed by post-inoculation ambient temperature W or LA spray. Tissue samples were collected pre- and post-treatment to enumerate STEC populations. The experiment was a completely randomized design with four replicates.
Results: STEC attachment levels to lean and fat tissues were similar across scenarios (P > 0.05). LA reduced STEC levels more effectively than water (P ≤ 0.05). A significant treatment by scenario interaction was observed for STEC reductions, with LA being more effective in scenarios A and B (pre-rigor inoculation) than C and D (post-rigor inoculation).
Significance: LA spray is more effective for pre-rigor carcasses compared to chilled beef surfaces for reducing STEC. For laboratory studies, consideration must be given to when inoculum is applied to tissue surfaces to accurately determine effectiveness of antimicrobial treatments. Variability in pathogen inoculation protocols for carcasses and subprimals appears in the literature; complicating process control determinations and antimicrobial intervention comparisons. These findings provide guidance to processors and researchers regarding inoculation protocols and their potential impacts on microbiological results.