Efficacy of Roselle (Hibiscus sabdariffa) Calyx Formulations against Escherichia coli O157:H7 on Bagged Organic Leafy Greens

Introduction: The increased trend of fresh produce consumption in the past decade has been accompanied with an increase in associated outbreaks. Escherichia coli O157:H7 has been repeatedly implicated in these outbreaks. Since consumers prefer natural over synthetic products, and due to limitations of available sanitizers, we investigated the possibility of an alternative approach to washing organic leafy greens by evaluating the effectiveness of roselle (Hibiscus sabdariffa) formulations against E. coli O157:H7.

Purpose: The effectiveness of roselle tea and aqueous extract against E. coli O157:H7 in organic leafy greens was evaluated.

Methods: Organic leafy greens: baby and adult spinach, and romaine and iceberg lettuce were washed in sterile water, inoculated with a cocktail of E. coli O157:H7 (10⁶ CFU/ml), and dried to facilitate attachment. Roselle tea was obtained from dried calyces boiled in distilled water. Roselle aqueous extract (10, 20, and 30%; v/v in phosphate buffered saline; PBS), was prepared from fresh calyces. The inoculated leafy greens were individually treated with the roselle extract or tea and stored at 4ºC. Hydrogen peroxide, water, and PBS were used as the controls. Bacterial populations were enumerated from treated samples at days 0, 1, and 3 of storage.

Results: The antimicrobial activity of the tea and extract was dependent on antimicrobial concentration, storage time, and the type of produce (P < 0.01). By day 3, 30% roselle extract showed a reduction in bacterial population by 3.7 and 3.1 logs for baby spinach and romaine lettuce, respectively, and by 2 logs for the rest of the greens. By day 3, roselle tea showed a reduction in bacterial population of 3.4 logs for romaine lettuce, and of 1.1- to 2.3-logs for the rest of the greens.

Significance: Both, roselle tea and extracts can be used as effective wash treatments to inactivate Escherichia coli O157:H7 on organic leafy greens.