Reduction of an E. coli O157:H7 and Salmonella composite on fresh strawberries by varying antimicrobial washes and vacuum perfusion

A 2011 outbreak of hemorrhagic colitis, which resulted in the death of two individuals, was associated with contaminated strawberries. A study was conducted to identify antimicrobial washes effective at reducing E. coli O157:H7 and Salmonella enterica from the surface of fresh whole strawberries during two-minute immersion washes. Twenty-seven antimicrobial treatments were tested. Vacuum perfusion was applied to strawberries during chlorine and peracetic acid treatments to promote infiltration of sanitizer into porous strawberry tissue. Strawberries were inoculated to 7.1 log CFU/strawberry with a seven-strain bacterial composite, consisting of three strains of E. coli O157:H7 and four serovars of Salmonella enterica. Berries were air-dried for 2 h and immersed in circulating antimicrobial solutions for 120 s at 22 °C. Four treatments reduced ≥ 3.0 log CFU/strawberry, including (a) 1% acetic acid + 1% H2O2, (b) 30% ethanol + 1% H2O2, (c) 90 ppm peracetic acid, and (d) 1% lactic acid + 1% H2O2. Two additional treatments that reduced 2.8 log CFU/strawberry were (a) 40% ethanol, and (b) 1% each of phosphoric + fumaric acids. Eight treatments reduced 2.0-2.6 log CFU/strawberry. Five treatments reduced < 1.45 CFU/strawberry, including (a) 1% citric acid, (b) 1% lactic acid, (c) 1% acetic acid, (d) 0.5% each of acetic + citric acids and (e) 0.5% each of acetic + lactic acids. The use of vacuum perfusion with 200 ppm chlorine or 90 ppm peracetic acid did not reduce greater populations of pathogens than did the same treatments without vacuum perfusion. Fourteen treatments reduced no more pathogens (p < 0.05) than did sterile deionized water. Results from this study provide some options for end-point decontamination of strawberries for retail operations just prior to serving to customers.