One-step sample preparation for convenient examination of volatile monoterpenes and phenolic compounds in peppermint leaves using deep eutectic solvents

Deep eutectic solvents (DESs) were investigated as an extraction medium for one-step sample preparation for chemical characterization of peppermint (Mentha piperita L.). Rather than applying discontinuous, time-consuming extraction methods to prepare two types of extracts, peppermint leaves were extracted efficiently into a DES, which was composed of choline chloride and d-(+)-glucose at a 5:2 molar ratio. The produced peppermint extracts contained volatile monoterpenes and phenolics at levels sufficient for direct chemical examination of peppermint leaves. The extracted monoterpenes in DES could be quantified via a newly developed method based on headspace solid-phase microextraction coupled to gas chromatography. The same extracts were also directly used to assess phenolics in terms of total phenolic content, total flavonoid content, and antioxidant activity. The proposed method allowed one-step sample preparation for extraction of volatile monoterpenes and phenolics of peppermint leaves and could be applied to various peppermint samples obtained from different origins.