Zsuzsanna Pluhár

Determination of polyphenolic compounds by liquid chromatography-mass spectrometry in Thymus species

Polyphenolic compounds represent a wide group of phytochemicals, including well-known subgroups of phenolic acids, flavonoids, natural dyes, lignans etc., which are produced by plants. These natural bioactive compounds possess a variety of beneficial effects including antioxidant and anticarcinogenic activities, protection against coronary diseases as well as antimicrobial properties. Thymus species have already been reported as sources of different phenolic acids and flavonoids. Moreover, the composition and content of flavonoids in Thymus species play important role as taxonomic markers providing distinction of species. High-performance liquid chromatography (HPLC) coupled with diode array detector (DAD) and on-line mass spectrometry (ESI-MS) method was used for analysis. The method was evaluated for a number of validation characteristics (repeatability and intermediate precision, LOD, LOQ, calibration range, and recovery). The polyphenolic pattern of five native Hungarian Thymus species (T. glabrescens Willd., T. pannonicus All., T. praecox Opiz, T. pulegioides L., and T. serpyllum L.) was characterized. The dominant compound was rosmarinic acid, which ranged between 83.49 μg g(-1) and 1.436 mg g(-1). Other phenolic acids (ferulic acid, caffeic acid and its other derivatives, chlorogenic acid and p-coumaric acids) were present in every examined Thymus species, as well as flavanones: naringenin, eriodictyol and dihydroquercetin; flavones: apigenin and apigenin-7-glucoside, flavonols: quercetin and rutin. The polyphenolic pattern was found to be a useful additional chemotaxonomic tool for classification purposes and determination of the locality of origin.

Evaluation of Environmental Factors Influencing Essential Oil Quality of Thymus pannonicus All. and Thymus praecox Opiz

ABSTRACT In wild growing populations, higher essential oil levels have been detected in Thymus pannonicus (T. pannonicus; 0.005–1.103 ml/100 g DW) than in T. praecox (Creeping thyme) (0.005–0.110 ml/100 g DW). T. pannonicus tolerated a variety of substrates and vegetation types, but preferred a slightly acidic or neutral pH and elevated levels of K, Ca, Mg, Mn, Fe, Co, and Cr in soil. T. praecox could survive only on calciferous substrate of wild habitats and could not tolerate soil extremes or serious disturbances. T. pannonicus was a thymol (25–41%)/p-cymene (17–38%) chemotype, while T. praecoxwas a geraniol (18–23%)/germacrene D (14–16%)/β-caryophyllene (4–12%) chemotype. The thymol concentration was positively correlated with humus, N, K, Mg, and Cd contents of the soil.

Essential oil composition and preliminary molecular study of four Hungarian Thymus species

Chemical and genetic differences of twenty taxa belonging to four Thymus species were studied in order to determine whether molecular characters and essential oil components could be used as taxonomic markers and to examine the correlation between them. Plant samples, representing different taxa and geographic regions, were collected from experimentally grown populations. Essential oil samples were analysed by GC/MS and cluster analysis of volatile composition resulted in segregation of thymol chemotypes from sesquiterpenic ones. Thymol was characteristic for all the populations of Thymus glabrescens and T. pannonicus as well as for certain taxa belonging to T. praecox and T. pulegioides. Sesquiterpenes occurred in only two taxa of T. glabrescens, in each sample of T. praecox and in three taxa of T. pulegioides. Plant samples were analysed by random amplified polymorphic DNA (RAPD). The obtained dendrogram revealed high gene diversity. The 13 primers resulted 114 polymorphic RAPD bands, and the average percentage of polymorphism was 80.8%. The RAPD dendogram showed separation neither at interspecific nor at interpopulational levels. Therefore, further specific molecular studies involving more taxa are suggested. Partial correlation have been found between molecular and chemical assessments.

Morphological and Physiological Plant Responses to Drought Stress in Thymus citriodorus

Water availability is considered as a determinant factor that affects plant growth. The commercial medicinal values of an aromatic plant rely on the presence of secondary metabolites that are affected under water shortage. Two-year-old Thymus citriodorus plants were subjected to different polyethylene glycol (PEG-6000) levels (0, 2%, and 4%) under greenhouse condition. PEG treatment lasted for 15 days. Thyme plant showed a morphological drought avoidance mechanism by maintaining the root system development through shoot fresh weight reduction resulting in promoted root absorption capacity and sustained plant growth. Moreover, stressed plants were able to maintain water use efficiency and root : shoot ratio suggesting a strong relation between root water uptake and water use saving strategies. Furthermore, thyme plants reduced tissue dehydration through stomatal closure and improved root water uptake. Content of volatile oil constituents of geraniol and diisobutyl phthalate increased upon drought stress while pseudophytol was reduced. Unexpectedly, thymol was not reported as a main oil element under either control or mild stress condition, while it was increased upon high drought stress in measure of 4.4%. Finally, carvacrol significantly accumulated under high drought stress (

Studies on Occurence, Essential Oil Data and Habitat Conditions of Hungarian Thymus pannonicus and Thymus glabrescens Populations

Thymus pannonicus and T. glabrescens flowering shoots are gathered from wild populations. Dried aerial parts contain active compounds used in the therapy of coughing and possess strong antimicrobial activity. Eight natural habitats, involving 17 populations of the two species were found in 2010, where the essential oil characteristics of the flowering shoots and soil parameters have been determined. The highest essential oil level (1.079 mL/100 g) have been detected in the T. pannonicus sample collected near Balatongyorok. Concerning average essential oil amounts, T. pannonicus samples accumulated 0.566 mL/100 g, while those of T. glabrescens produced 0.083 ml/100 g. High thymol ratio is an important qualitative trait: fairly high levels (51.1-65.6%) were found in samples of T. pannonicus. T. pannonicus population, growing on rhyolite tuff in Bukk Mountains, had low essential oil content with sesquiterpene chief compounds and without thymol. Regarding essential oils of T. glabrescens, the major compounds were sesquiterpenes (germacrene D, β-caryophyllene, caryophyllene oxide), with low amount of thymol (<5%). Our results approve data of the previous literature, concerning generalist and pioneer characters of both species with eurytopic attitude, tolerating different soil parameters (pH, salt %, NPK and CaCO3 content). Strong positive correlation have been found between the p-cymene and γ-terpinene ratios (r=0.951), while the latter compounds were in medium positive correlation with thymol percentage (r=0.387 and 0.481, respectively). It was also proven statistically that the essential oil content correlated negatively with high ratio of sesquiterpenes.

Effect of water supply on growth and polyphenols of lemon balm (Melissa officinalis L.) and thyme (Thymus vulgaris L.)

A pot experiment was carried out with lemon balm (Melissa officinalis L.) and thyme (Thymus vulgaris L.). Different water supply was applied: 25%, 40% and 70% saturation of soil water capacity (SWC). Morphological traits, biomass and phenolic type active ingredients were investigated. Among the two species, main differences were registered in biomass and TPC. Lower SWC resulted in reduced biomass production of lemon balm, while the applied stress treatments did not effect the biomass of thyme. In lemon balm, highest TPC contents were measured in control plants both in shoots and roots but in thyme, the shoots showed a significantly increased TPC at the 25% SWC conditions. Neither the content of total flavonoids nor that of the rosmarinic acid was affected by the treatments. The antioxidant capacity proved to be in tight connection with the TPC in both species (r = 0.766-0.883). The rosmarinic acid content of lemon balm plants contributed to the antioxidant capacity, as well (r = 0.679-0.869).