title: Critical Concentration of Lecithin Enhances the Antimicrobial Activity of Eugenol against Escherichia coli.
abstract: Lecithin is a natural emulsifier used in a wide range of food and nonfood applications to improve physical stability, with no known bioactive effects. In this study, the effect of lecithin on the antimicrobial performance of a constant eugenol concentration was tested against threeEscherichia colistrains (C600, 0.1229, and O157:H7 strain ATCC 700728). This is the first study, to our knowledge, focusing on lecithin at concentrations below those commonly used in foods to improve the stability of oil in water emulsions (≤10 mg/100 ml). For all three cultures, significant synergistic antimicrobial effects were observed whenE. colicultures were exposed to a constant eugenol concentration (ranging from 0.043 to 0.050% [wt/wt]) together with critical lecithin concentrations ranging from 0.5 to 1 mg/100 ml. Increasing the concentration of lecithin above 1 mg/100 ml (up to 10 mg/100 ml lecithin) diminished the antibacterial effect to values similar to those with eugenol-only treatments. The formation of aggregates (<100 nm) at the critical lecithin concentration was observed using cryo-transmission electron microscopy (cryo-TEM), together with a reduction in light absorbance at 284 nm. At critically low concentrations of lecithin, the formation of nanoscale aggregates is responsible for improving eugenol antimicrobial effects.IMPORTANCEEssential oils (EOs) are effective natural antimicrobials. However, their hydrophobicity and strong aromatic character limit the use of essential oils in food systems. Emulsifiers (e.g., lecithin) increase the stability of EOs in water-based systems but fail to consistently improve antimicrobial effects. We demonstrate that lecithin, within a narrow critical concentration window, can enhance the antimicrobial properties of eugenol. This study highlights the potential bioactivity of lecithin when utilized to effectively control foodborne pathogens.
authors.affiliation: Department of Food Science, The Pennsylvania State University, University Park, Pennsylvania, USA.
authors.forename: Haoshu
authors.initials: H
authors.lastname: Zhang
authors.affiliation: Department of Food Science, The Pennsylvania State University, University Park, Pennsylvania, USA.|Center for Molecular Immunology and Infectious Disease, The Pennsylvania State University, University Park, Pennsylvania, USA.
authors.forename: Edward G
authors.initials: EG
authors.lastname: Dudley
authors.affiliation: Department of Food Science and Technology, University of Tennessee, Knoxville, Tennessee, USA.
authors.forename: P Michael
authors.initials: PM
authors.lastname: Davidson
authors.affiliation: Department of Food Science, The Pennsylvania State University, University Park, Pennsylvania, USA fede@psu.edu.
authors.forename: Federico
authors.initials: F
authors.lastname: Harte
mesh_terms: D000890:Anti-Infective Agents / Q000494:pharmacology*; D015169:Colony Count, Microbial; D004655:Emulsions; D019453:Escherichia coli O157 / Q000187:drug effects*; D005054:Eugenol / Q000494:pharmacology*; D005516:Food Microbiology; D054709:Lecithins / Q000032:analysis*; D008826:Microbial Sensitivity Tests; D009822:Oils, Volatile / Q000494:pharmacology
chemical_list: D000890:Anti-Infective Agents; D004655:Emulsions; D054709:Lecithins; D009822:Oils, Volatile; D005054:Eugenol
keywords: Escherichia coli; antimicrobial activity; eugenol; lecithin