Abstract
Mentha species are widely used as food, medicine, spices, and flavoring agents. Thus, chemical composition is an important parameter for assessing the quality of mints. In general, the contents of menthol, menthone, eucalyptol, and limonene comprise one of the major parameters for assessing the quality of commercially important mints. Building further on the phytochemical characterization of the quality of Mentha species, this work was focused on the composition of phenolic compounds in methanolic extracts. Thirteen Mentha species were grown under the same environmental conditions, and their methanolic extracts were subjected to the LC–MS/MS (liquid chromatography–tandem mass spectrometry) profiling of phenolics and the testing their biological activities, i.e., antioxidant and tyrosinase inhibition activities, which are important features for the cosmetic industry. The total phenolic content (TPC) ranged from 14.81 ± 1.09 mg GAE (gallic acid equivalents)/g for Mentha cervina to 58.93. ± 8.39 mg GAE/g for Mentha suaveolens. The antioxidant activity of examined Mentha related with the content of the phenolic compounds and ranged from 22.79 ± 1.85 to 106.04 ± 3.26 mg TE (Trolox equivalents)/g for M. cervina and Mentha x villosa, respectively. Additionally, Mentha pulegium (123.89 ± 5.64 mg KAE (kojic acid equivalents)/g) and Mentha x piperita (102.82 ± 15.16 mg KAE/g) showed a strong inhibition of the enzyme tyrosinase, which is related to skin hyperpigmentation. The most abundant compound in all samples was rosmarinic acid, ranging from 1363.38 ± 8323 to 2557.08 ± 64.21 μg/g. In general, the levels of phenolic acids in all examined mint extracts did not significantly differ. On the contrary, the levels of flavonoids varied within the species, especially in the case of hesperidin (from 0.73 ± 0.02 to 109. 39 ± 2.01 μg/g), luteolin (from 1.84 ± 0.11 to 31.03 ± 0.16 μg/g), and kaempferol (from 1.30 ± 0.17 to 33.68 ± 0.81 μg/g). Overall results indicated that all examined mints possess significant amounts of phenolic compounds that are responsible for antioxidant activity and, to some extent, for tyrosinase inhibition activity. Phenolics also proved to be adequate compounds, together with terpenoids, for the characterization of Mentha sp. Additionally, citrus-scented Mentha x villosa could be selected as a good candidate for the food and pharmaceutical industry, especially due its chemical composition and easy cultivation, even in winter continental conditions.
Highlights
Phenolic compounds belong to the most frequent and widespread groups of plant metabolites, with more than 8000 identified structures to date
Values of gallic acid equivalents (GAEs) for the total phenolic content and quercetin equivalents (QEs) for flavonoid content are summarized in Supplementary Table S1
The lowest values for both total phenolics and flavonoids were found in the extract of Mentha cervina (14.81 ± 1.09 mg GAE/g and 3.65 ± 0.037 mg QE/g), while the extract of Mentha suaveolens was found to be richest in total phenolics (58.93 ± 8.39 mg GAE/g) and M
Summary
Phenolic compounds belong to the most frequent and widespread groups of plant metabolites, with more than 8000 identified structures to date. The importance of plant phenolics (flavonoids, phenolic acids, etc.) is widely known in human health care These bioactive plant secondary metabolites have been an inexhaustible source of scientific research, including their isolation from plant extracts, the assessment of their chemical structure, and the characterization of a wide array of biological properties [1,2]. The antioxidant ability of phenolic components occurs mainly through a redox mechanism and allows the components to act as reducing agents, hydrogen donors, singlet oxygen quenchers, and metal chelators [3]. This antioxidant mechanism has an important role in the reduction of lipid oxidation in tissues—both plant and animal. Plant phenolics are beneficial because they conserve the quality of plant-based food and food products and reduce the risk of the development of some human disorders, such as cardiovascular diseases, arteriosclerosis, cancer, diabetes, cataract, disorders of cognitive function, and neurological diseases [1,2,3]
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