Antibacterial effect of free, nanoemulsified and protein-complexed carvacrol

Essential oils (EOs) are aromatic compounds known for their potent anti-inflammatory and antibacterial properties. However, these molecules are susceptible to degradation when exposed to external conditions, such as light and oxygen. Numerous studies have reported the protective effects of encapsulation on sensitive bioactive, such as EOs, for improved or preserved stability and shelf life. The aim of this study was to investigate the antibacterial activity of different formulations of carvacrol, the most important and used component of EOs. We comparatively evaluated the activity of free, protein-complexed and nano-emulsified carvacrol against two selected pathogenic bacteria: Staphylococcus aureus (a Gram+ strain) and Escherichia coli (a Gram- strain). Free carvacrol exhibited antibacterial activity against both tested bacteria, with comparable minimum inhibitory concentrations of 380 µg/mL for S. aureus and 370 µg/mL for E. coli. Indeed, carvacrol interact strongly with lactoferrin and β-lactoglobulin, two model carrier proteins, with preserved antibacterial activity. Unexpectedly, nano-emulsification of carvacrol, resulting in nano-droplets of 100 to 240 nm, decreased its antibacterial effect. Therefore, complexation with food proteins is a viable option to formulate a carrier with preserved carvacrol bioactivity. Ongoing studies aim to understand the reasons behind the recovered low activity of nano-emulsified carvacrol on the two pathogen species and under used experimental set-up.