Phenolic Profile , Mineral Content and Antibacterial Activity of the Methanol Extract of Vaccinium myrtillus L .

Bilberry is considered as one of the most economically important wild berries. However, bilberry is not enough investigated, and there are only a few published works. Therefore, we performed in one place complete qualitative analysis, antimicrobial activity against different Gram-positive and Gram-negative bacteria and contents of metals. In our research, it was found that bilberry contains different active phenolic compounds, such as chlorogenic acid, delphinidin glycoside, delphinidin arabinoside, cyanidin glycoside, cyanidin arabinoside, malvidin glycoside, peonidin glycoside, and malvidin arabinoside. The content of metals was different in leaves and fruits. In our samples, the content of aluminum, boron, barium, calcium, cadmium, chromium, copper, iron, manganese, nickel, phosphorus, silicon and zinc was higher, and contents of potassium, magnesium, and sodium were lower than in bilberry samples investigated in Latvia. Antimicrobial activity of investigated extracts was evaluated against laboratory control strains from ATCC collection, Gram (+) bacteria: Staphylococcus epidermidis ATCC 12228, Staphylococcus aureus ATCC 6538, Streptococcus pyogenes ATCC 19615, Enterococcus faecalis ATCC 19433, Propionibacterium acnae ATCC 11827, and Gram (-) bacteria: Escherichia coli ATCC 9863, Pseudomonas aeruginosa ATCC 9027, Acinetobacter boumanii ATCC 196060, Proteus mirabilis ATCC 12453, Klebsiella pneumonia ATCC 10031, and against related strains isolated from human wound swabs. V. myrtillus extract was less potent against strains from wounds compared to ATCC strains as well Gram (-) bacteria compared to Gram (+) bacteria. The most sensitive strains were St. epidermidis, St. pyogenes, P. mirabilis and S. aureus.

Absorption UV-VIS spectra were recorded on DADdetector (with a total spectral range between 200 nm and 800 nm).MS analysis was performed using LCQ 3D-ion trap mass spectrometer with electrospray ionization (ESI) in the negative, and in positive ion mode.The ESI source parameters for negative mode were set as follows: source voltage 4.5 kV, capillary voltage -41 V, tube lens voltage -95 V, capillary temperature 350 ºC, sheath and auxiliary gas flow (N2) 32 and 8 (arbitrary units), respectively.On the other hand, the ESI source parameters for positive ion mode were: source voltage 4.5 kV, capillary voltage 19 V, tube lens voltage 95 V, capillary temperature 275 ºC, sheath and auxiliary gas flow (N2) 32 and 8 (arbitrary units), respectively.MS spectra (both modes) were obtained by full range acquisition of m/z 130-900.For fragmentation study (MS/MS), a data dependent scan was performed by deploying the collision-induced dissociation (CID).The normalized collision energy of the CID cell was set at 15 and 25 eV, for the negative and positive mode, respectively.

Determination of the mineral content
Wet digestion of fruits To 0.5 g of dried sample 5 mL conc.HNO3 was added and placed on the hot plate for 1 h, and semi-dried; again, 5 mL of conc.HNO3 were added and 2 ml of H2O2 and kept on the hot plate for 1 h and after getting semi-dried cooled and filtered using Whatman filter paper, and the volume of the residue was made up to 25 mL with 2N HNO3 and taken to the Atomic absorption spectrophotometer for mineral analysis using Aluka standards (AOAC, 1990).

Dry method for leaves
The sample of dried leaves (2 g) was placed into a furnace for 2 h at 250 °C.Afterwards, the temperature was gradually increased to 550 °C, and calcined for another 12 h.The ash was covered with 5 mL conc.HNO3, filtered through quantitative filter paper, the pot was rinsed a couple of times using 0.5% HNO3 and made up to 25 mL using 0.5% HNO3.Results were expressed in mg/kg of dry residue (Azcue and Mudroch, 1994;Mateos-Aparicio et al., 2010).
Our aim was de facto to give in one place complete qualitative analysis, antimicrobial activity against different Gram-positive and Gram-negative bacteria, and contents of metals.To the best of our knowledge nobody before us performed this kind of the investigation.

Extraction
Bilberries (Vaccinium myrtillus L.) were used from the period of the fully ripe stage in July 2015 in woods from Lake Vlasina, Serbia.Fresh fruits were stored at -20 °C for one week when extracts were prepared.The extraction method was modified and improved according to the already reported method (Može et al., 2011).Frozen samples (150 g) were firstly homogenized in 0.5 L ice-cold deoxygenated methanol that had previously been flushed for a few minutes with nitrogen.The homogenate was extracted for 1 h by shaking on magnetic stirrer IKA REO Basic C (Königswinter, Germany) at room temperature.The extract was filtered by vacuum through the technical filter paper.The residue was extracted again in 0.25 L icecold deoxygenated methanol for 0.5 h and the suspension was filtered as before.The third time the residue was extracted as described before.Finally, all three filtrates samples were pooled, flushed with nitrogen for a few minutes, and then stored at -20 °C until analysis.

Ultra high-performance liquid chromatography -diode array -electrospray ionization mass spectrometry analysis
The liquid chromatography (UHPLC) runs were carried out using Dionex Ultimate 3000 UHPLC+ system equipped with a diode array (DAD) detector and also connected with LCQ Fleet Ion Trap Mass Spectrometer (Thermo Fisher Scientific, USA).The separations were performed on the Hypersil gold C18 column (50×2.1 mm, 1.9 μm) of the same producer, at 25 ºC.The mobile phase was made from (A) 0.1% formic acid in water and (B) 0.1% 123 Gram (-) bacteria: Escherichia coli ATCC 9863, Pseudomonas aeruginosa ATCC 9027, Acinetobacter boumanii ATCC 196060, Proteus mirabilis ATCC 12453, Klebsiella pneumonia ATCC 10031, and against related strains isolated from human wound swabs.
Micro-well dilution method Minimum inhibitory (MIC) and minimum bactericidal concentrations (MBC) of extracts were determined by employing the broth micro-well dilution method with some modifications (Cockerill et al., 2012).An overnight culture of tested bacterial strains was used for the preparation of suspensions (0.5 McFarland standard turbidity).A serial doubling dilution of the extracts (in 10% aqueous dimethyl sulfoxide-DMSO) was prepared in a 96 well microtiter plate with inoculated Mueller Hinton broth (MHB) at concentrations ranging from 0.06-126 mg mL -1 .The final volume was 100 µL, and the final concentration of bacterial suspensions was 10 6 CFU mL -1 in each well.The plates were incubated for 24 h at 37 0 C. Metronidazole, doxycycline, ciprofloxacin, and gentamicin were used as positive control (Sigma Aldrich, St Louis, MO, USA), and dilutions were at concentrations ranging from 0.01 to 100 mg mL -1 .All determinations were performed in triplicate.Microbial growth was determined by adding 20 µL of 0.5% triphenyl tetrazolium chloride (TTC) aqueous solution in microtiter plates.In order to determine MBC, the broth was taken from each well and inoculated on Mueller Hinton agar (MHA) for 24 h at 37 °C.The MBC is defined as the lowest concentration of the extracts at which 99.9% of inoculated bacteria were killed.

Results and Discussion
Qualitative analysis of phenolic compounds Although we followed the experimental procedure of Može et al. (2011), fewer compounds in the investigated extracts were found in our case.Isolated compounds using UHPLC method were identified using literature by the comparison of the mass spectra (Table 1).Our results were in accordance with Hokkanen et al. (2009) and Laaksonen et al. (2010), too. Latti et al. (2008) observed the high variation in the content of anthocyanins in bilberries from different parts of Finland (northern berries have higher contents than southern).The same explanation can be prescribed for our sample and results for berries north from Serbia.Riihinen et al. (2008) claim that most of the phenolic acids and flavonols can be found in the leaves rather in berries of bilberry.

Determination of the content of metals
The content of metals was found to be different in leaves and fruits.The performed investigation showed that the content of aluminium, boron, barium, calcium, cadmium, chromium, copper, iron, manganese, nickel, phosphorus, silicon and zinc is higher than those found by Skesters et al. (2014) (Table 2).On the other hand, contents of potassium, magnesium, and sodium were lower than in bilberry found from the same research group (Skesters et al., 2014) (Table 2).(1.80) cyanidin-glycoside 449 287 (100%), 317 (Nakajima et al., 2004;Xianli and Prior, 2005) 517, 279 nm 6.

Conclusions
Bilberry as a source of bioactive agents is not investigated enough, so we performed the complete analysis of metals, complete qualitative analysis and determined the antibacterial activity of the extract.We found that it contains different active phenolic compounds, such as chlorogenic acid, delphinidin glycoside, delphinidin arabinoside, cyanidin glycoside, cyanidin arabinoside, malvidin glycoside, peonidin glycoside, and malvidin arabinoside.The contents of metals in leaves and fruits vary, and in some cases they are higher, and sometimes lower than found by others.Antimicrobial effect of the V. myrtillus extract was less potent against strains from wounds compared to ATCC strains as well Gram (-) bacteria compared to Gram (+) bacteria.The most sensitive strains were St. epidermidis, St. pyogenes, P. and S. aureus and therefore the fruit extract of the investigated plant may find use as an additive in creams for skin care and protection.

Table 1 .
Isolated compounds from bilberry, their characteristic ions from mass spectra and UV/VIS adsorption characteristics

Table 2 .
Element concentrations (mg/g wet weight±standard deviations, n=3) in bilberry.Sample 1 was prepared from dried leaves, and sample 2 from fresh fruit

Table 3 .
Antimicrobial activity (MIC/MBC in mg/mL) of Vaccinium myrtillus L. methanol extract and referent antibiotics against pathogenic