Antioxidant Properties and Bioactive Compounds of Oregano, Sage, Basil, Rosemary, and Herbal Mixtures

Herbs and spices are traditionally added to food in cuisines around the world. Antioxidant activity and content of bioactive compounds were compared in oregano, sage, basil, rosemary, and herbal mixtures. After optimization of ultrasound-assisted extraction of the ethanol-water extracts, the content of reducing compounds of the herb extracts was tested using the Folin-Ciocalteu method, and antioxidant capacity was evaluated with ABTS (2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid)diammonium salt) and DPPH (2,2-diphenyl-1-picrylhydrazyl radical) assays. Oregano showed the highest antioxidant activity in all tests used (2.6 mg of gallic acid equivalent (GAE) per mL in the Folin-Ciocalteu test, 4.6 mg Trolox/mL in the ABTS assay, and 3.3 mg Trolox/mL in the DPPH assay) while rosemary had the lowest antioxidant activity (1.2 mg GAE/mL (Folin-Ciocalteu), 1.5 mg Trolox/mL (ABTS), and 1.3 mg Trolox/mL (DPPH)). Apart from antioxidant properties, the content of bioactive compounds was determined with the use of high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS). It was found that in all tested Lamiaceae herbs and the herbal mixes, rosmarinic acid widely predominates as a major non-volatile phenolic constituent, and its content varies from 1121 µg/g in rosemary to 10,255 µg/g in herbes de Provence. High concentrations were also observed for quinic acid in both oregano and rosemary. Interestingly, the concentrations of rosmarinic acid in the group of herbs studied are positively correlated with the results obtained in the Folin-Ciocalteu, ABTS, and DPPH tests (Spearman's correlation coefficient 0.7030, 0.6657, and 0.7188, respectively), whereas no such correlation is observed for quinic acid. Overall, the findings indicate that these herbs share a common hydroxycinnamate-based phytochemical framework but display clear species-specific differences reflecting their intrinsic metabolism. Furthermore, the concentration of 3-caffeoylquinic acid in the Sicilian herbs (1021 µg/g) was approximately 10 times higher compared to the samples of Dalmatian herbs, herbes de Provence, and pure herbs, which demonstrates the unique chemical composition of that mixture, including the presence of dried tomatoes and tarragon, which were not included in other tested herbal mixtures.