Evaluation of STEC on Beef Intended for Non-intact Use After Treatment with Microwaves and Low Temperature Storage

Shiga toxin-producing Escherichia coli (STEC) is a preeminent concern for the beef industry because of its ability to produce life-threatening complications. Thus, the objective of this study was to evaluate the effectiveness of microwaves, in combination with either refrigeration or frozen storage, as a post-harvest, post-packaging intervention to reduce STEC (serogroups O157:H7, O26, O103, O111, O121, O45, and O145) on vacuum-packaged beef. Beef striploins samples inoculated with STEC, were treated with microwaves (MW, 472.6 kW/s), or assigned for control (CTR, not subjected to microwaves). All samples were stored either at refrigeration (0–4°C) or frozen storage temperature (-18°C or below). The microbial analyses were performed at day 1, 5, 10 (cold storage) or at 7, 14, and 21 days (frozen storage) by surface swab sampling. The bacterial count results showed that samples under frozen storage had a greater reduction of inoculated STEC than that of samples subjected to refrigeration temperature (P < 0.001); however, microwave-treated samples did not undergo significant STEC reductions compared with controls (P < 0.05). These results suggest that the microwave treatment used in this study did not contribute to STEC reduction; rather, the effects observed were the product of temperature storage causing significant bacterial reduction (P < 0.01).