Reduction of spoilage and pathogenic bacteria on beef products by direct and indirect applications of antimicrobial agents

A multiple-hurdle antimicrobial decontamination method for raw and ready-to-eat (RTE) beef may provide a means of effectively reducing microbial populations, thereby resulting in products with increased shelf-life and reduced potential for causing foodborne illness. In the first experiment, the efficacy of low molecular weight polylactic acid (LMW PLA) at extending the shelf life of raw beef was determined. Fresh beef pieces (2.5 by 2.5 by 2.5 cm) inoculated with Escherichia coli O157:117 or Lactobacillus plantarum were dipped in PLA solutions or wrapped in packaging films sprayed with 2% MW 240 PLA, 2% MW 360 PLA, an equal mix of the two, water or 1% Tween 20, with an exception of one set of control beef samples without treatment. Beef samples were then vacuum-packaged and stored at 4°C. Beef surface pH values and numbers of E. coli O157:117 and L. plantarum were determined weekly. Throughout storage, samples of beef treated with MW 360 PLA maintained a significantly lower pH ( P < 0.05) compared to the untreated, water and Tween 20 treated controls. At 0 d, dip treatment with MW 360 PLA and equal mix of MW 240 and 360 PLA reduced surface pH values of the beef samples inoculated with E. coli O157:117 to 4.74 and 4.77, respectively, from 5.62. MW 360 PLA reduced the population of E. coli O157:117 and L. plantarum by 5.76 and 6.50 log CFU/cm2 from the initial numbers of 6.67 and 7.58 log CFU/cm2, respectively. Spraying on the film used for packaging raw beef with PLA, demonstrated a 7.29 log reduction of E. coli O157:117 and 1.26 log reduction of L. plantarum numbers, respectively, over a storage time of 3 wk. In the second experiment, fresh beef pieces inoculated with E. coli O157:117, Listeria monocytogenes or Staphylococcus aureus was sprayed with 0.5% cetylpyridinium chloride (CPC), 0.12% acidified sodium chlorite (ASC), 0.1% potassium sorbate (PS) or an equal mix of the two solutions. A CPC spray on raw beef and absorbent tray pads, resulted in 2.9 and 4.01 reductions in log numbers of L. monocytogenes and S. aureus, respectively, at the end of storage. An equal mix of CPC and PS reduced E. coli O157:117 numbers by 2.09 log, L. monocytogenes by 1.53 log and S. aureus by 3.99 log at 14 d, respectively. In the third experiment, the efficacy of CPC, ASC and an equal mix of the two at reducing numbers of E. coli O157:117, L. monocytogenes and S. aureus spiked on the sliced roast beef was determined. (Abstract shortened by UMI.)...