Polyphenol extraction in microwave reactor using by-product of Thymus serpyllum L. and biological potential of the extract

In the present study, polyphenol extraction from Thymus serpyllum by-product (herbal dust) in microwave reactor was optimized through varying extraction time, ethanol concentration and solid-to-solvent ratiovia determination of total polyphenol and flavonoid contents, and antioxidant activity, using response surface methodology and a central composite design. Total polyphenol and flavonoids contents, as well as antioxidant activity of the extracts were statistically significantly affected by ethanol concentration and solid-to-solvent ratio. However, extraction time had statistically significant influence only on polyphenol yield. The extraction conditions that maximized polyphenol recovery were 48% ethanol and 0.0402 g/mL solid-to-solvent ratio during 86 s of microwave-assisted extraction, and under these conditions total polyphenol content was estimated to be 57.2 mg of gallic acid equivalents (GAE)/L, while measured value was 58.1 ± 3.2 mg GAE/L. Polyphenol content (HPLC analysis), antioxidant, antimicrobial and antispasmodic potential of the extract prepared under these optimal extraction conditions were evaluated. Rosmarinic acids, luteolin 7-O-glucuronide, caffeic acid, apigenin glucuronide, 6-hydroxyluteolin 7-O-glucoside, 6,8-di-C-glucosylapigenin, and traces of chlorogenic acid were quantified in the extract (descending order of content). The selected extract inhibited 95% ± 0.9 of lipid peroxidation in β-Carotene and linoleic acid emulsion. It was more effective against tested Gram-positive bacteria than against Gram-negative and showed dose-dependent antispasmodic activity on spontaneous contractions, acetylcholine- and potassium chloride-induced contractions. Microwave-assisted extraction could be selected as a successful technique for polyphenol extraction from wild thyme by-product. Biological activities shown in the study open the possibility of potential application of the extract in pharmaceutical, food, functional food and cosmetic products.