Physical and antimicrobial properties of cinnamon bark oil co-nanoemulsified by lauric arginate and Tween 80

Abstract

Lauric arginate (LAE) is a water-soluble cationic surfactant which has antimicrobial activity against a broad spectrum of foodborne pathogens. Some spice essential oils are effective lipophilic antimicrobials. Combining both antimicrobials may reduce their usage levels and possible negative sensory impacts when applied in complex food matrices. The objective of this study was to combine a nonionic surfactant (Tween 80) with LAE to form stable nanoemulsions with cinnamon bark essential oil (CBO) and to characterize the antimicrobial activity of these nanoemulsions. CBO was homogenized at 1% w/w in the aqueous phase with 3% w/w Tween 80 and 0.05-0.375% w/w LAE, followed by heating at 90°C for 30min to obtain final emulsions. With 0.125% and higher LAE, transparent emulsions with ~100nm in hydrodynamic diameter were observed to be stable during 30-day storage at 21°C. Antimicrobial activities of the nanoemulsion prepared with Tween 80 and 0.375% w/w LAE were studied. The respective minimum inhibitory concentrations (MICs) of the nanoemulsion in tryptic soy broth (TSB) were 12, 7, and 8ppm LAE for Salmonella enteritidis, Escherichia coli O157:H7, and Listeria monocytogenes, while those of free LAE were 11, 6, and 6ppm, respectively. MICs of CBO were 400ppm for the tested bacteria and Tween 80 at 6% w/w did not show inhibitory effect. Growth kinetics of the bacteria in TSB treated with the nanoemulsion or individual components at concentrations corresponding to the MICs of free LAE showed that binding among the LAE and Tween 80 and CBO components resulted in the antibacterial activity of nanoemulsion being lower than same concentrations of free LAE and CBO. Conversely, little difference was observed for the individual antimicrobials and the nanoemulsion in 2% reduced fat milk, and 750ppm LAE and 2000ppm CBO were observed to be the dominant antimicrobial against Gram-positive and Gram-negative bacteria, respectively. The growth of L. monocytogenes in 2% reduced fat milk at 4°C was not observed when treated by the nanoemulsion corresponding to 187.5ppm LAE and 500ppm CBO. Therefore, stable and transparent nanoemulsions of EOs can be prepared with the combination of LAE and Tween 80 without compromising antimicrobial activities.

Keywords: Antimicrobial activity; Cinnamon bark oil; Lauric arginate; Nanoemulsion; Polysorbate 80.