Purpose: The overall goal of this project was to evaluate the effectiveness of microwaves as a postharvest intervention to reduce STEC (Serotypes O157:H7, O26, O103, O111, O121, O45, and O145) on vacuum packaged beef stored under refrigerated or frozen conditions.
Methods: Beef strip loins were sectioned into three equal parts, which were randomly assigned to Microwave treatment (MW, treatment using novel microwave with six magnetrons, applying 472.6 kWs of energy per run), control (CTR, inoculated, vacuum packaged, but not treated), or INOC (section used to determine STEC attachment). For each individual microorganism, sections were stored at refrigeration (0 to 4°C) or frozen (-17°C or below). Microbial analyses were made at day 1, 5, and 10 (cold storage) or at 7, 14, and 21 days (frozen storage). Swabs were obtained from each of the beef sections, diluted with 10 ml BPW, and plated onto MacConkey Agar for enumeration. The experiment was replicated three times.
Results: The analysis of variance for each serotype shows statistical significance for storage type with a P-value of <0.001 for all serotypes. The samples stored under refrigeration presented statistically higher STEC concentration in CFU/100 cm2 compared with the ones in frozen storage. Moreover, the samples with serotype O121, O111, O103, O45, and O26, stored under refrigeration, showed a statistical significance for treatment with a P-value of 0.01. Only samples with serotype O45 shown statistical significance for treatment, in frozen storage.
Significance: The results showed that under the experimental parameters the microwave treatment was not effective in reducing the STEC on fresh, refrigerated vacuum beef. However, under frozen conditions, STEC concentrations of beef strip loins could potentially be reduced up to 99.9%.