Ineffectiveness of Hot Acid Sprays to Decontaminate Escherichia coli O157:H7 on Beef

The efficacy of warm (20°C) and hot (55°C) acetic, citric and lactic acid sprays on survival of Escherichia coli O157:H7 on raw beef was determined. Fresh, raw beef sirloin tips were sliced into ca. 1-cm slices with a sanitized slicer. Discs (5-cm diameter, ca. 25-g) were then taken from internal areas of each slice and inoculated with a 5-strain mixture of E. coli O157:H7 such that final populations on beef samples were 10³ or 10⁶ CFU/g. After standing for 15 min, each inoculated disc was sprayed with 1 mi of 0, 0.5, 1.0 and 1.5% of each acid at 20 or 55°C using an atomizer. Acid-treated meat samples were allowed to dry for 15 min and held at 5°C for up to 13 days in sterile plastic pouches. Escherichia coli O157:H7 was acid tolerant, and acids did not differ appreciably in their lack of antimicrobial activity on E. coli O157:H7. For example, reductions in populations differed by <0.3 log_l0 CFU/g immediately after treatment and < 0.5 log_l0 CFU/g after 13 days incubation, compared to untreated Controls. None of the acid treatments appreciably reduced E. coli O157:H7 on beef samples nor were any of the acid treatments judged effective for practical uses.