Cold-pressed oregano (Origanum vulgare) oil: a rich source of bioactive lipids with novel antioxidant and antimicrobial properties

Abstract

In this investigation, cold-pressed oregano (Origanum vulgare) oil (OO) was studied for its lipid classes, fatty acid profile, tocols and phenolics contents. Radical scavenging potential against DPPH· and galvinoxyl radicals was determined. Antimicrobial properties of OO against foodborne bacteria, food spoilage fungi and dermatophyte fungi were also evaluated. The level of neutral lipids in OO was the highest, followed by glycolipids and phospholipids. The main fatty acids in OO were linoleic, oleic, stearic and palmitic acids. γ-Tocopherol constituted 32.1 % of total measured tocols followed by α-tocotrienol (25.8 %) and γ-tocotrienol (21.3 %). OO contained high amounts of phenolic compounds (5.6 mg/g as GAE). OO had strong antiradical action wherein 72 % of DPPH· radicals and 60 % of galvinoxyl radical were quenched after 60 min of incubation. Rancimat assay showed that induction time (IT) for OO/sunflower oil blend (1:9, v/v) was 6 h, while OO/sunflower oil blend (2:8, v/v) recorded higher IT (8 h). OO inhibited the growth of all tested microorganisms. The highest antimicrobial activity of OO was recorded against the dermatophyte fungi including T. mentagrophytes (42 mm) and T. rubrum (38 mm), followed by food spoilage fungi including A. flavus (36 mm) and C. albi (32 mm) with minimal lethal concentration (MLC) ranging between 40 and 320 μg/mL. OO exhibited also broad-spectra activity against foodborne pathogen bacteria (S. aureus, E. coli, S. enteritidis and L. monocytogenes) with MLC ranging between 160 and 320 μg/mL. The results suggest that OO could be used economically as a valuable natural product with novel functional properties in food, cosmetics and pharmaceutical industries.