Antioxidant Properties of Aqueous Extracts from Selected Lamiaceae Species Grown in Turkey

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Abstract
Water-soluble extracts from black thyme (Thymbra spicata L.), savory (Satureja cuneifolia Ten.), Spanish oregano (Coridothymus capitatus (L.) Reichb. f.), sweet marjoram (Majorana hortensis Mœnch), Syrian oregano (Origanum syriacum L.), Toka oregano (Origanum minutiflorum O. Schwarz et P. H. Davis), and Turkish oregano (Origanum onites L.) were screened for antioxidant properties in a battery of six in vitro assays. Total phenol content and qualitative−quantitative compositional analyses were also carried out. The extracts demonstrated varying degrees of efficacy in each screen. The savory extract was the most effective at reducing iron(III), scavenging 1,1-diphenyl-2-picrylhydrazyl radicals, inhibiting ascorbate-iron(III)-catalyzed hydroxyl radical-mediated brain phospholipid peroxidation, and site-specific hydroxyl radical-mediated 2-deoxy-d-ribose degradation. The Syrian oregano extract was the most effective chelator of iron(II), while Spanish and Turkish oregano extracts were the most effective inhibitors of nonsite-specific hydroxyl radical-mediated 2-deoxy-d-ribose degradation. All the extracts contained Folin−Ciocalteu reagent-reactive substances, which was confirmed by the presence of polar phenolic analytes (i.e., hydroxybenzoates, hydroxycinnamates, and flavonoids). Keywords: Antioxidants; chelation; composition; DPPH•; high performance liquid chromatography; hydroxyl radical; iron reduction; Lamiaceae; water-soluble extracts