Antioxidant and antimicrobial activities of essential oils obtained from oregano (Origanum vulgare ssp. hirtum) by using different extraction methods.

In this study, antioxidant and antimicrobial activities of essential oils obtained from oregano (Origanum vulgare ssp. hirtum) were determined by using solvent-free microwave extraction (SFME), supercritical fluid extraction, and conventional hydrodistillation (CH) methods. The inhibitory effects on the 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) radical of essential oils obtained from oregano by using SFME and CH were similar. However, essential oil extracted by CH showed greater (2.69 μmol/μL of oil) Trolox equivalent antioxidant capacity (TEAC) than oregano oils obtained by SFME (P < .05). The difference between percentage inhibition and TEAC values most probably is due to the fact that undiluted and diluted samples are used in the percentage inhibition assay and the TEAC assay, respectively. TEAC values of oregano essential oils obtained by SFME at different microwave power levels were found to be similar and ranged from 0.72 to 0.84 μmol/μL of oil. Essential oils obtained by CH and SFME at different microwave powers inhibited the survival of Listeria monocytogenes, Salmonella typhimurium, and Escherichia coli O157:H7, whereas survival of Staphylococcus aureus was not influenced. In addition, oregano oil obtained by SFME at 40% power level did not show any inhibitory effect on E. coli O157:H7.