Exploitation of the biological potential of Satureja thymbra essential oil and distillation by-products

- The distillation waste of Satureja thymbra L. was valorized as bio-active.
- The main polyphenols were identified.
- The essential oil and solid residue extracts presented antimicrobial activity.
- The ethyl acetate extract depressed oxidation in palm oil.
- The ethanol extract depressed oxidation in palm oil-in-water emulsion.

Dried leaves of Satureja Thymbra were subjected to water-steam distillation to recover the essential oil (EO) and the water extract (Aq). The solid by-product was subjected to sequential Soxhlet extraction with ethyl acetate (EAc) and ethanol (EtOH). The obtained extracts were analysed by HPLC-DAD-ESI-MS/MS and the main flavonoids and phenolic acids were identified and quantified. The high antiradical activity of the extracts, as estimated by the DPPH assay, was correlated to their total phenol content. Moreover, the antioxidant activity of the extracts was tested in bulk palm oil and palm oil-in-water emulsions. EAc extract prolonged the induction period and reduced by 42% the rate of peroxide formation in palm oil, while EtOH extract was the most effective in emulsions. Additionally, the EtOH and EAc extracts depressed the growth of Listeria monocytogenes in emulsions deliberately spiked with 100 cfu/mL.The antimicrobial properties of EO, Aq, EAc, and EtOH extracts were assayed and the minimum inhibitory and non-inhibitory concentration values were determined. EO was effective against Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, Listeria monocytogenes, Salmonella Εnteritidis, Salmonella Typhimurium, Pseudomonas fragi, Saccharomyces cerevisiae and Aspergillus niger. In contrast, EAc and EtOH extracts were active only against the bacteria species, but not against S. cerevisiae and A. niger, while no antimicrobial activity was observed for Aq extract.