Evaluation of combinations of essential oils and essential oils with hydrosols on antimicrobial and antioxidant activities

Context: Essential oils (EO) are commonly extracted from plants by steam distillation in which an aqueous phase called hydrosol (HD) is obtained. Unlike EO, hydrosol studies have been limited despite the interest of the food, cosmetic and phytotherapeutic industries to find natural preservative alternatives to synthetic ones. Aims: To evaluate the in vitro antimicrobial and antioxidant efficacies of combinations of essential oils (EOs) and essential oils and hydrosols (HDs) of Lippia alba, Rosmarinus officinalis, and Thymus vulgaris. Methods: The EOs and HDs were characterized by gas chromatography with flame ionization detector and gas chromatography coupled with mass spectrometry. Then, they were screened against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Candida albicans and Aspergillus Niger using the microdilution method for the four first strains and the agar diffusion method for Aspergillus Niger. Antioxidant capacity was evaluated using ABTS method. Results: Interactions between essential oils, and essential oils and hydrosols were found to be as microbicide, and for the first time, antioxidant using the fractional inhibitory concentration. When compared with individual EOs, EO-EO combinations diminished the microbicide minimum concentration. Conclusions: The Thymus vulgaris EO-HD combination, in comparison with individual extracts, diminishes by four times the MBC against Escherichia coli and decrease by half their antioxidant capacity.