Purpose: To screen sanitizing solutions for decontaminating Escherichia coli O157:H7 (EHEC) and Salmonella enterica serovars from strawberries.
Methods: Four serovars of Salmonella (serovars Saintpaul, Montevideo, Newport, and Stanley) and three strains of EHEC were grown individually in TSB + 100 ppm nalidixic acid (TSBN), washed by centrifugation and combined into a seven-strain inoculum. Strawberries were flooded with the inoculum three times and dried under a laminar flow hood for 2 hours. Strawberries were then washed for 2 min within respective sanitizing solutions at 21 °C, and diluted 1:2 (weight:volume) with Dey-Engley neutralizing broth. Strawberries were macerated with a hammer in filtered bags and pummeled in a stomacher for 2 min. Homogenate was plated on TSAN + 0.1% sodium pyruvate, incubated for 24 h at 37 °C, and colonies were enumerated.
Results: Inoculation levels were 7.07 log CFU/strawberry. Rinsing with water reduced populations by 1.24 log. The only treatments capable of inactivating > 3 log of pathogens were (log CFU/strawberry inactivation in parenthesis) 40% ethanol (3.02), and 0.1M sulfuric acid (5.21). Results of other rinses are as follows: 85 ppm paracetic acid (2.84), 0.5% each of lactic and citric acids (2.74), 3% H2O2(2.46), 0.33% each of lactic + citric + acetic acids (2.11), 0.1N NaOH (1.84), 200 ppm chlorine (1.73), 30% ethanol (1.59), 1% lactic or 0.5% each of lactic and acetic acids (1.41), 1% acetic acid (1.34), and 0.5% each of acetic and citric acids (1.23).
Significance: Salmonella and EHEC inoculated onto strawberries are very resistant to inactivation by sanitizing solutions (as has been demonstrated with other types of fresh produce). Common commercial rinses (e.g., 200 ppm chlorine and 85 ppm paracetic acid) inactivated only 0.5 and 1.6 log more cells than did rinsing with water alone, indicating that more effective commercial sanitizers are needed for inactivating pathogens on strawberries.