Inactivation of Escherichia coli O157:H7 on baby spinach by aqueous and aerosolized antimicrobials
Date
2011
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Publisher
University of Delaware
Abstract
An increasing number of outbreaks associated with fresh produce such as baby spinach have been reported in the last two decades with Escherichia coli O157:H7 being one of the most frequent causative agents. Chlorinated water has been widely used by food industry to wash these fresh commodities, but this washing procedure has limited efficacy and can lead to the formation of carcinogenic substances. Thus, more effective and safer treatment methods are needed to control pathogens in fresh produce. In our first study, several generally recognized as safe organic acids and hydrogen peroxide in combination with mild heat (40 and 50 ̊C) was tested for their efficacies against E. coli O157:H7 on baby spinach. Chlorinated water (200 ppm free chlorine) only reduced the population of E. coli O157:H7 on baby spinach by 1.2-1.6 log CFU/g, which was not significantly different from DI water washing. Washing with 1% lactic acid (LA) alone or in combination with citric acid or hydrogen peroxide (H2O2) at 40 ̊C for 5 min was the most effective treatment achieving a 2.7 log reduction of E. coli O157:H7. In the second study, aerosolization was investigated as a potential way to apply allyl isothiocyanate (AIT), H2O2, acetic acid (AA) and LA on fresh baby spinach to control E. coli O157:H7 during 10 days of storage at 4 ̊C. Treatment of aerosolized 5% AIT resulted in > 5 log reduction of E. coli O157:H7 on spinach regardless if the samples are pre-washed or not; however, this treatment impaired the sensory quality of leaves. Addition of LA to AIT improved the efficacy of AIT against E. coli O157:H7 during the storage. Treatment of 3% H2O2 washing followed by a 2-min treatment of aerosolized 1% AIT + 2.5% LA reduced E. coli O157:H7 on spinach leaves by 4.8 log CFU/g after 10 days storage at 4 ̊C without causing noticeable adverse effects on the appearance of samples. Therefore, low dose application of AIT in combination with LA has the potential to control E. coli O157:H7 on fresh produce.