Decontamination of iceberg lettuce by some plant hydrosols

• Thyme, summer savory and oregano hydrosols showed antibacterial activity.
• Summer savory hydrosol showed the highest inhibition rate against Escherichia coli O157:H7.
• Thymol was major compound in oregano, summer savory and thyme hydrosols.
• Use of bay leaf and sideritis hydrosols in lettuce were accepted by the panelists.

Hydrosols are byproducts obtained by steam distillation of plant materials. In this study, six hydrosols obtained from thyme (Thymus vulgaris L.), summer savory (Satureja hortensis L.), rosemary (Rosmarinus officinalis L.), salvia (Salvia officinalis L.), sideritis (Sideritis canariensis L.), oregano (Origanum onites L.) and bay leaf (Laurus nobilis L.) were used for decontamination of fresh-cut iceberg lettuce inoculated with Salmonella enterica subsp. enterica serovar. Typhimurium, Listeria monocytogenes and Escherichia coli O157:H7. Volatile composition of the hydrosols and sensorial properties of hydrosol-treated lettuce were also investigated. Thyme and summer savory hydrosols achieved ∼3–4 log reductions on all bacterial strains tested while significant (P < 0.05) reductions were obtained by all hydrosol treatments depending on the treatment time (0, 20, 40 or 60 min). Thymol and 1,8 cineole were the most abundant volatile constituents of the hydrosols, likely affecting their antibacterial activity. Hydrosol-treated samples especially with bay leaf and sideritis were generally accepted by the panelists. This study confirmed that plant hydrosols could be successfully used as sanitizing agents for fresh-cut lettuce to provide their microbiological safety without causing deep sensorial defects on the products.