Evaluating the Efficacy of Olive, Apple and Grape Seed Extracts in Reducing Escherichia coli O157:H7 Contamination on Organic Leafy Greens during the Wash Process

Powdered extracts of apple, olive, and grape seed were evaluated for antimicrobial activity against Escherichia coli O157:H7 during processing and subsequent short-term storage of organic leafy greens. The leafy greens tested were, baby spinach, mature bunched spinach, romaine lettuce, and iceberg lettuce. The organic leafy greens were thoroughly washed and inoculated with a three-strain cocktail of E. coli O157:H7 (6 log CFU ml-1). Antimicrobial treatments of the extracts, prepared in phosphate buffered saline, at 1, 3, and 5% concentrations were used to wash contaminated leafy greens which were then stored for 3 days at 4ºC. Surviving E. coli O157:H7 populations were enumerated on days 0, 1, and 3 of storage. Significant reductions (P<0.05) in pathogen populations were observed in all the leafy greens following treatment with the plant extracts. Between 2.9-5.3 log CFUg-1 reductions in E. coli O157:H7 population were observed with all three concentrations (1%, 3% and 5%) of olive extract by day 3, for all the leafy greens. The 5% olive extract treatment reduced the pathogen to undetectable levels by day 0 for romaine lettuce and by day 1 for iceberg lettuce and baby spinach. Apple extract at 5% concentration showed reductions of 3.4 and 3.9 log CFUg-1 in iceberg and romaine lettuce, respectively. The 5% grape seed extract reduced E. coli O157:H7 populations by 4.4 logsCFUg-1 in romaine lettuce. This study demonstrates the potential of olive, apple and grape seed extracts as antimicrobial wash treatments against E. coli O157:H7 during the processing of organic leafy greens.