Medicinal herbs are a good source of bioactive compounds with antioxidant and antimicrobial activity. In some cases that can also be poisonous due to the heavy metals content. In our study we assumed a high biological activity and low level of hazard mineral compounds, providing the possibility of using these herbs in different kinds of industry.

The medicinal herbs were collected from nature and gardens in Slovakia (the Year 2018; locality Runina; 560 m.a.s.l.): Zingiber officinale Rosco – rhizome, Symphytum officinalis L. – root, Valeriana officinalis L. – root, Cichorium intybus L. – root, Armoracia rusticana Gaertn – root and Allium ursinum L. – leaves. Before the analysis samples were pulverized in the mortar.

The sample – 0.2 g was extracted with 20 mL of 80% ethanol for 2 hours. After centrifugation at 4000 rpm (Rotofix 32 A, Hettich, Germany) for 10 min, the supernatant was used for measurement (antioxidant activity, polyphenols, flavonoids, phenolic acids). All analyses were realized in triplicate.

All chemicals were analytical grade and were purchased from Reachem (Slovakia) and Sigma Aldrich (USA).

Six strains of microorganisms were tested in this study. Gram-negative bacteria: Escherichia coli CCM 2024, Citrobacter freundii CCM 7187, Yersinia enterocolitica CCM 7204 and Gram-positive bacteria: Bacillus cereus CCM 7934, Staphylococcus aureus subsp. aureus CCM 2461, Listeria monocytogenes CCM 4699. All tested strains were collected from the Czech Collection of microorganisms. The bacterial suspensions were cultured in the nutrient broth (Imuna, Slovakia) at 37 °C.

The antimicrobial activity of each extract was determined by a disc diffusion method. Briefly, 100 μL of the test bacteria were grown in 10 mL of fresh media until they reached a count of approximately 10⁵ cells per mL. Then 100 μL of the microbial suspension was spread onto Mueller Hinton agar plates. The extracts were tested using 6 mm sterilized filter paper discs. The diameters of the inhibition zones were measured in millimeters. All measurements were to the closest whole millimeter. Each antimicrobial assay was performed in at least triplicate. Filter discs impregnated with 10 μL of distilled water were used as a negative control.

The amount of mineral elements was analysed by the ICPOES method (ICP-OES spectrophotometer, Thermo iCAP Dual 6500, USA) – the samples (0.2 g) were subjected to mineralization under high pressure, in HNO3 65%, super pure. The samples were weighed and placed in Teflon vessels which were then filled with 8 mL of nitric acid and sealed tightly. For each group of nine samples, during the microwave dissolution process, the rotor of the digestion system was additionally filled with a blank sample comprising 8 mL of nitric acid alone. The samples were digested for one hour, with the applied algorithm of temperature increase as specified for biological samples, without exceeding 200 °C. This was carried out using Ethos One microwave digestion system from Milestone. The vessels were opened after the mineralization process had been completed and the samples with acid had been brought to room temperature. The samples were cooled down to room temperature and supplemented with water to the volume of 50 mL. The obtained detection threshold for each element was not lower than 0.01 mg.kg^-1 (with the assumed detection capacity of the measuring apparatus at a level exceeding 1 ppb). The measurements were performed with ICP-OES spectrometer, Thermo iCAP Dual 6500 with horizontal plasma, and the capacity of detection along and across plasma flame (Radial and Axial). Before measuring each batch of samples the method was calibrated with the use of certified Merck models. The measurement result for each element was compensated to account for the measurement of elements in the blank sample. In each case, a 3-point calibration curve was used for each element, with optics correction applying the method of internal models, in the form of yttrium and ytterbium ions, at the concentrations of 2 mg.L^-1 and 5 mg.L^-1, respectively.

All experiments were carried out in triplicate and the results reported are expressed as means with standard deviations. The experimental data were subjected to the analysis of variance (Duncan's test), at the confidence level of 0.05, using the SAS 2009 (USA) software.

Antioxidant activity (Table 1) of analysed samples tested by the DPPH method ranged from 0.61 to 3.62 mg TEAC.g^-1. The highest value was determined in the sample of ginger, following by a sample of chicory and valerian. Antioxidant activity tested by the phosphomolybdenum method (Table 1) had a similar tendency – the highest value was measured in a sample of ginger (204.14 mg TEAC.g^-1). Similar value determined in ginger by reducing power method Akinola, Ahmad and Maziah (2014) – 266.95 mg TEAC.g^-1 The strong activity by DPPH, ABTS, and FRAP method of ginger was observed in the study of Mustafa et al. (2019). This authors also reported that activity is influenced by the technological process – the best activity in FRAP and ABTS method was found in ginger sun-dried, while in the DPPH method the strongest activity was found in fresh ginger. Antioxidant activity of valerian was observed in the study of Pilerood and Prakash (2014). These authors tested ethanol, methanol, acetone, 80% methanol, and 80% ethanolic extracts of valerian. The best activity determined by using 80% of ethanol – this extraction solution was also used in our study. In a sample of ramsons (Table 1) by the DPPH method was evaluated the lowest activity, whereas by the phosphomolybdenum method the activity was very strong. This result can be explained by the mechanism of action – in the DPPH method antioxidants from the sample act as scavengers of radical, whereas in phosphomolybdenum method antioxidants from the sample act as reductant agent. In the study of Putnoky, Caunii and Butnariu (2013) are described that the S–oxyde (+/−) of S–2–propenyl cysteine and the S–oxide of S–alkenyl cysteine, located in the cytoplasm and the enzyme alliinase located in the vacuole is the main bioactive compounds which bind reactive free radicals and act as reductant agent.

Total polyphenols (Table 1) in tested samples ranged from 4.37 to 13.19 mg GAE.g^-1. The highest value was found in the sample of ramsons following by ginger and valerian. Lachowicz et al. (2017) determined in ramsons values ranged from 6.5 (bulbs) to 42.5 (leaves) mg GAE.100g^-1fresh matter which is lower values compared to our study. Pejatović, Samardžić and Krivokapić (2017) determined values ranged from 13.05 to 18.33 mg GAE.g^-1, which is comparable with our findings. Qadir et al. (2017) in ginger extract found total polyphenols in the amount of 98.37 mg GAE.100g^-1, which is a lower level to compare with our results. These authors also published that 80% of ethanol is discovered more effective for the recovery of antioxidants from herbal plants to compare with methanol and acetone.

Total flavonoids (Table 1) in tested samples ranged from 1.07 to 47.55 mg QE.g^-1. The best value was measured in a sample of ramsons following by a sample of ginger and comfrey. Pejatović, Samardžić and Krivokapić (2017) determined in ramsons leaves extract values ranged from 13.75 to 20.00 mg QE.g^-1. Ghasemzadeh, Jaafar and Rahmat (2010) in a sample of ginger extract determined total flavonoids in amount ranged from 3.66 to 4.21 mg QE.g^-1, which are lower values to compare with our results. These authors by HPLC method determined that in ginger rhizomes the most abundant flavonoid is quercetin. In valerian the most abundant flavonoids are 6-methylapigenin and hesperidin, which are responsible for the sedative and sleep-enhancing properties of valerian root (Marder et al., 2003).

Total phenolic acid content (Table 1) ranged from 0.99 to 9.77 mg CAE.g^-1. The highest value was determined in a sample of ginger following by a sample of ramsons and comfrey. Fahmi et al. (2019) published that chlorogenic acid (63.85 ppm) and hesperidin (156.91 ppm) are among the major phenolic and flavonoid constituents in dry ginger. In comfrey Sowa et al. (2017) by HPLC-DAD method found rosmarinic, p-hydroxybenzoic, caffeic, chlorogenic, and p-coumaric acid.

In a sample of ginger (Table 2) was observed activity to inhibit B. cereus CCM 7934, Y. enterocolitica CCM 7204 and L. monocytogenes CCM 4699. In the study of Nas, Ali and Ahmad (2018) E. coli were found to be the highest susceptible organisms with an average zone of inhibition of 13.6 mm, followed by the Shigella spp. (13.3 mm), Salmonella typhi (12.7 mm), Staphylococcus aureus (12.5 mm), Pseudomonas aeruginosa (10.8 mm) while the least average zone of inhibition is shown by Klebsiella pneumoniae (9.2 mm).

In the sample of horseradish (Table 2) was detected low potential to inhibit growing of B. cereus CCM 7934 and L. monocytogenes CCM 4699. In comfrey extract (Table 2) was detected activity to inhibit E.coli CCM 2024, C. freundii CCM 7187, Y. enterocolitica CCM 7204 and L. monocytogenes CCM 4699. The antibacterial activity of the root extract of Symphytum officinale was tested by the disc diffusion method in the study of Sumathi, Kumar and Bai (2011) and it was found that methanol extract showed maximum inhibitory effect against the Proteus vulgaris and Staphylococcus aureus.

In ramsons sample (Table 2) was observed slight activity to inhibit E. coli CCM 2024, C. freundii CCM 7187, Y. enterocolitica CCM 7204, S. aureus subsp. aureus CCM 2461 and L. monocytogenes CCM 4699. Krivokapic et al. (2018) reported that the antimicrobial activity of the plant extract is influenced by the extraction solvent. A methanol extract of ramsons has been shown to exhibits antimicrobial activity against bacteria including Staphylococcus aureus, Bacillus subtilis, Escherichia coli, Proteus mirabilis, Salmonella enteritidis. On the other hand, water extract was efficient only against Bacillus subtilis. Chicory extract in our study showed slight activity to inhibit E. coli CCM 2024, B. cereus CCM 7934, Y. enterocolitica CCM 7204, S. aureus subsp. aureus CCM 2461 and L. monocytogenes CCM 4699. In the study, Liu et al. (2013) were observed several extracts of chicory which displayed activities against Escherichia coli, Staphylococcus aureus, Bacillus thuringiensis, Bacillus subtilis, and Salmonella typhi. These authors also found that the best method for the chicory extract yield with antimicrobial activity was a combination of 70% ethanol v/v, 24-h impregnation time, 3 sonication rounds, and 300-W ultrasonic input power. In valerian extract (Table 2) was observed potential to inhibit the growth of C. freundii CCM 7187, Y. enterocolitica CCM 7204, B. cereus CCM 7934, S. aureus subsp. aureus CCM 2461 and L. monocytogenes CCM 4699.

The results of mineral compounds composition are presented in Table 3. In a sample of ginger was determined potassium as the dominant compound following by magnesium and phosphorus. Very interesting was the amount of zinc which was the highest in this sample compared to other tested samples. According to Chasapis et al. (2012) zinc is one of the most important trace elements in the human body, with three major biological roles: catalyst, structural, and regulatory ion. Zinc has an important effect on homeostasis, immune function, oxidative stress, apoptosis, aging, and significant disorders of great public health interest are associated with zinc.

In samples of horseradish were dominant potassium, sulphur, calcium and phosphorus. The amount of sulphur was higher to compare with ginger, valerian, chicory, and comfrey. A higher amount of sulphur can be explained as the fact that horseradish is rich for glucosinolates. Glucosinolates are N-hydroxy-sulfates with a highly variable side chain and a sulfur-linked beta-dglucopyranose. These compounds are the precursor molecules of the biologically active isothiocyanates components (Bertóti et al., 2019).

In a sample of comfrey dominant compounds was potassium, following by sodium, phosphorus, and calcium. This sample was determined the highest value of copper, which is an essential mineral for human health but at the same time can be toxic, depending upon the amounts of ingested. Copper is associated with bone health, immune function, and increased frequency of infections, cardiovascular risk, and alterations in cholesterol metabolism (Araya, Manuel and Fernando, 2007).

In the sample of ramsons was determined potassium as dominant compounds following by the sulphur, calcium, and magnesium. The amount of sulphur was the highest to compare with the other analysed samples. It is not surprising whereas the dominant bioactive compounds of this plant are based of sulphur (allicin).

In the sample of chicory, the main mineral compounds were potassium, sodium, magnesium and sulphur. The same tendency was observed in the study of Mona, Wafaa and Elgindy (2009) in which also authors determined higher content of iron in chicory root, which is comparable with our findings.

In the sample of valerian was determined potassium as dominant mineral compounds following by calcium and magnesium. In this sample was found the highest value of aluminium, this amount can be evaluated as a safe because according to Food Safety Authority (Stahl et al., 2017) the tolerable weekly intake of aluminium is 1 mg.kg^-1 body weight for all groups of people.

Valerian root is used mainly in folk medicine to prepare a decoction to treat psychical problems and usually is not consumed as a vegetable. Generally, the amount of heavy metals in observed samples was detected only in a trace amount, so our results reveal that the medicinal herbs do not represent in this study a potential health risk regarding the content of toxic elements.