Efficacy of roselle (Hibiscus sabdariffa) calyx formulations against Escherichia coli O157:H7 during flume-washing of organic leafy greens

Foodborne outbreaks due to contaminated fresh produce, including organic leafy greens, have increased in the last twenty years. Several of these outbreaks have been associated with Escherichia coli O157:H7 infections. The limited availability of approved antimicrobial washes for organic leafy greens warrants the need to seek alternative approaches by the organic produce industry. The present study evaluated the use of roselle (Hibiscus sabdariffa) calyx formulations as flume-tank wash treatments for four types of organic leafy greens (iceberg and romaine lettuce, and mature and baby spinach). These formulations were prepared as either 10, 20, or 30% concentrations (v/v) of roselle aqueous extract or as 100% concentration (v/v) of roselle tea. Leafy greens were inoculated with a cocktail of 3 E. coli O157:H7 strains and washed with appropriate antimicrobial treatments. Treated leafy greens were tested for surviving E. coli O157:H7 populations on 0, 1, and 3 days. Results from the study indicated a 1.4-2.5 log cfu (colony forming units)/g reduction overall for the 20% concentration of roselle extract by day 3, on all leafy greens. Baby spinach treated with 30% roselle extract showed a 3.7 log cfu/g reduction in pathogen population by day 3. Treatment with roselle tea resulted in 2.0-3.4 log cfu/g reductions of E. coli O157:H7 for all leafy greens by the third day. This study demonstrates the potential of roselle calyx formulations for reduction of E. coli O157:H7 populations during flume-washing of organic leafy greens.