Purpose: The study compares the survival and growth behavior of E. coli O157:H7 on damaged portions of the most widely consumed raw salad vegetables in the Egyptians' diet (arugula, green cabbage, leek, lettuce, radish, and spinach) stored at different abusive temperatures.
Methods: Damaged leaves were inoculated with a four-strain cocktail of approximately 105 CFU E. coli O157:H7 per leaf. Total aerobic microorganisms and surviving populations of E. coli O157:H7 were periodically enumerated after different storage times. The pH, moisture content, total phenolic content (TPC), total flavonoid content (TFC), and anti-oxidant capacity (AOC) for control un-inoculated leaves were determined. Data were analyzed with One-Way ANOVA and post hoc least significance difference.
Results: Storage of damaged leaves at 8°C for 4 days led to different outcomes of surviving E. coli O157:H7 populations possibly due to interference of background microorganisms. High TPC, TFC, and AOC in spinach leaves stored at 15°C for 3 days resulted in pathogen growth inhibition. Insignificant (P > 0.05) differences in population counts on damaged arugula leaves stored at 15°C and room temperature were owed to antibacterial activities of glucosinolates and ascorbic acid induced at elevated temperatures. Increased population counts on damaged leek and arugula held at room temperature for 3 days by 4 and 1.7 log units, respectively, was associated with high moisture retention (96%) and increase in final pH (6.82).
Significance: This is the first study conducted in Egypt on the influence of abusive storage temperatures on microbiological quality and safety of salad vegetables. In regard to Egypt’s warm climate, considerations must be given by health authorities and Food Safety Agency to the provided data that match conditions of retail display and consumer home storage, to be implemented for risk assessment and development of intervention measures that remove or limit the growth of foodborne pathogens in leafy green category should contamination inadvertently occur at any stage of the production chain.