| Abstract [eng] |
The title of the Master’s thesis by Rasa Pesliakaitė is “Comparison of Phenolic Compound Amount and Essential Oil Composition in Leaves, Inflorescences and Stems of Various Mint Taxa“ Rationale: The pharmacological effects of mint are mainly related to the accumulation of essential oils and phenolic compounds. The amount and composition of these secondary metabolites may vary depending on the plant part, taxon and flowering period. Due to their widespread use, increasing attention is being paid to the study of these medicinal plants in order to apply them for medical purposes. The aim of the research: To determine and compare the content of total phenolic compounds and the composition of essential oils in different plant parts of various mint taxa. Objectives of the research: 1) to compare the amount of essential oils in different plant parts of Mentha longifolia, Mentha spicata, Mentha spicata var. crispa, Mentha × villosa, Mentha suaveolens, Mentha arvensis, Mentha aquatica, Mentha × piperita 'Zgadka' and Mentha × piperita 'Prilukskaja'; 2) to compare the content of total phenolic compounds in different plant parts of these mint taxa; 3) to compare the amounts of essential oils and total phenolic compounds in different plant parts of these mint taxa during the first and second flowering periods; 4) to compare the chemical composition of essential oils in the leaves and inflorescences of these mint taxa during the first and second flowering periods. Methodology of the research: Plant material was collected during the first and second flowering periods and dried at room temperature. The total phenolic compounds was determined by UV spectrophotometry using the Folin-Ciocalteu reagent and expressed as gallic acid equivalents. Essential oils were extracted by hydrodistillation using a Clevenger-type apparatus. The chemical composition of essential oils was determined by gas chromatography-mass spectrometry. Study results and conclusions: The highest content of total phenolic compounds was found in M. × villosa leaves during the first flowering period (64.62 ± 0.29 mg GAE/g), while the lowest was detected in M. aquatica stems (9.70 ± 0.12 mg GAE/g). In the studied Mentha taxa, total phenolic compounds were generally most abundant in the leaves. Their amount decreased in the inflorescences by 3.0 – 42.5 % between flowering periods, whereas in the leaves it increased or remained stable. The highest essential oil percentage was found in M. suaveolens inflorescences during the first flowering period (5.28 ± 0.09 %), while the lowest was found in M. × piperita 'Zgadka' stems during the first flowering period (0.05 ± 0.01 %). Regardless of the flowering period, the highest percentage of essential oils was observed in the inflorescences of all studied Mentha taxa. The percentage of essential oils in the leaves was significantly positively correlated with the percentage of essential oils in the inflorescences (r = 0.9, p < 0.05) during both flowering periods. In most Mentha taxa, the percentage of essential oils was higher in the inflorescences during the first flowering period, except for M. longifolia. Oxygenated monoterpenes constituted the largest proportion of essential oils. The main compound in peppermint essential oils was menthol, the percentage of which was generally higher during the second flowering period. In the other studied taxa, the main compound was carvone, which was most abundant in the inflorescences during the first flowering period. Overall, the results indicate that the content of total phenolic compounds and composition of essential oils depend on the mint taxon, plant part and flowering period. |
