Saša Mitrev

Development of a rapid and simple voltammetric method to determine total antioxidative capacity of edible oils

In this work we report on a new, rapid and simple voltammetric method to determine the total antioxidant capacity (TAC) of the edible oils. The method explores the ABTS radical (2,2-azinobis(3-ethylbenzothiazoline-6-sulphonic acid)) assay as a redox probe and it relays on measuring catalytic voltammetric currents. The electrocatalysis comprises redox regeneration of the electrochemically created ABTS(+) radical either by Trolox (6-hydroxy-2,5,7,8-tetramethychroman-2-carboxylic acid) or by antioxidants present in studied oils. The detection limit of the method is determined to be 0.5 mg/L of Trolox equivalent, being a slightly lower than the corresponding UV-VIS spectrophotometric method. Applying the proposed voltammetric method the total antioxidant capacity of three types of commercially available cold-pressed edible oils are determined, and the results are found to be in a very good agreement with those obtained by UV-VIS spectrophotometry. The reported voltammetric method is cheap, rapid and simple, and it can be used as a sustainable alternative to the UV-VIS methods for the determination of total antioxidant capacitance of oils and other liquid lipophilic nutrients. Potent antioxidant capacity of studied oils was also confirmed by electron paramagnetic resonance spectroscopy of superoxide anion produced by macrophages.

Hydroxylated derivatives of dimethoxy-1,4-benzoquinone as redox switchable earth-alkaline metal ligands and radical scavengers

Benzoquinones (BQ) have important functions in many biological processes. In alkaline environments, BQs can be hydroxylated at quinoid ring proton positions. Very little is known about the chemical reaction leading to these structural transformations as well as about the properties of the obtained hydroxyl benzoquinones. We analyzed the behavior of the naturally occurring 2,6-dimethoxy-1,4-benzoquinone under alkaline conditions and show that upon substitution of methoxy-groups, poly-hydroxyl-derivatives (OHBQ) are formed. The emerging compounds with one or several hydroxyl-substituents on single or fused quinone-rings exist in oxidized or reduced states and are very stable under physiological conditions. In comparison with the parent BQs, OHBQs are stronger radical scavengers and redox switchable earth-alkaline metal ligands. Considering that hydroxylated quinones appear as biosynthetic intermediates or as products of enzymatic reactions, and that BQs present in food or administered as drugs can be hydroxylated by enzymatic pathways, highlights their potential importance in biological systems.

Optimization and Validation of a Microwave Digestion Method for Multi-element Characterization of Vranec Wines

An analytical method for determination of multi-element composition of Vranec wines using microwave digestion for sample preparation and inductively coupled plasma mass spectrometry (ICP-MS) was optimized and validated. Best recoveries, ranging from 87 to 114xa0%, were obtained for all analyzed elements, using a volume of 5xa0mL wine and 5xa0mL HNO3 for sample microwave digestion. In total, 38 elements (Ag, Al, As, B, Ba, Be, Bi, Ca, Cd, Co, Cr, Cs, Cu, Fe, Ga, Ge, In, Li, Mg, Mn, Mo, Na, Ni, P, Pb, Pd, Rb, S, Sb, Se, Si, Sn, Sr, Te, Ti, Tl, V, Zn) were determined in wines. The calibration curves of all elements were linear with correlation coefficients (R2) ranging from 0.9920 for 11B to 1.0000 for 53Cr and 88Sr. The accuracy of the method was checked with a standard addition method showing good repeatability and reproducibility (relative standard deviation, RSD <10xa0%). Vranec wines were fermented with Saccharomyces cerevisiae yeast strains commercial Clos, RC212, D254, and BDX, and six autochthonous Vinalco yeasts. The content of total elements in all Vranec wines ranged between 348 to 678xa0mg/L, observing lower amounts in wines fermented with the autochthonous Vinalco yeast. The content of harmful elements, such as Pb and Cu, was below the maximal allowed concentration in all wines.

WILD PEAR - PYRUS PYRASTER AS A NEW HOST OF ERWINIA AMYLOVORA IN MACEDONIA

Fire blight, caused by Erwinia amylovora, for the last 20 years has been the most destructive disease of pear, apple, quince and several other members of the family Rosaceae in the Republic of Macedonia. E. amylovora is a quarantine pathogen that has already caused considerable damage to orchards, and shows the tendency to further spreading. Bacteria with colony morphology similar of those of E. amylovora were repeatedly recovered from twild pear (Pyrus pyraster) on a semi-selective medium and identified as E. amylovora based on morphological, pathological, biochemical, nutritional, physiological methods, BIOLOG and PCR. The detection of E. amylovora on wild pear (Pyrus pyraster) in our country casts doubt on the reported suitability of this species as a source of resistance for pear breeding.

ISOLATION AND MOLECULAR DETERMINATION OF THE FIRE BLIGHT PATHOGEN, ERWINIA AMYLOVORA, ISOLATED FROM APPLE TREES IN THE REPUBLIC OF MACEDONIA

Fire blight is a bacterial disease caused by Erwinia amylovora. It is one of the most destructive diseases of pome fruit trees, particularly affecting apple and pear trees. In the present study, 15 bacterial isolates were isolated from apple orchards displaying fire blight disease symptoms in the summer of 2015. They were identified as E. amylovora based on morphological, pathological and biochemical (BIOLOG) analyses, including PCR assays. The molecular characterisation of these isolates using PCR were performed with specific primers for conventional (single) PCR, as well as from PCR amplification of the 16S rRNA gene using universal primers. The PCR products were positive and had the expected length of 1.1 kb. There is little information about the presence of E. amylovora on apple trees in Macedonia. To the best of our knowledge, this is the first report of fire blight in apples caused by E. amylovora in the Republic of Macedonia.

New insights into the chemistry of Coenzyme Q-0: A voltammetric and spectroscopic study.

Coenzyme Q-0 (CoQ-0) is the only Coenzyme Q lacking an isoprenoid group on the quinoid ring, a feature important for its physico-chemical properties. Here, the redox behavior of CoQ-0 in buffered and non-buffered aqueous media was examined. In buffered aqueous media CoQ-0 redox chemistry can be described by a 2-electron-2-proton redox scheme, characteristic for all benzoquinones. In non-buffered media the number of electrons involved in the electrode reaction of CoQ-0 is still 2; however, the number of protons involved varies between 0 and 2. This results in two additional voltammetric signals, attributed to 2-electrons-1H(+) and 2-electrons-0H(+) redox processes, in which mono- and di-anionic compounds of CoQ-0 are formed. In addition, CoQ-0 exhibits a complex chemistry in strong alkaline environment. The reaction of CoQ-0 and OH(-) anions generates several hydroxyl derivatives as products. Their structures were identified with HPLC/MS. The prevailing radical reaction mechanism was analyzed by electron paramagnetic resonance spectroscopy. The hydroxyl derivatives of CoQ-0 have a strong antioxidative potential and form stable complexes with Ca(2+) ions. In summary, our results allow mechanistic insights into the redox properties of CoQ-0 and its hydroxylated derivatives and provide hints on possible applications.

Halophytes in Republic of Macedonia

Republic of Macedonia is situated in Balkan Peninsula with a total area of 25,942 km2 and 1.26 million hectares of agricultural land, where 560,000 ha are arable land (44.2%) mainly located in the valleys and 700,000 ha are pastures (55.6%), located in hilly and mountainous regions of the country. There are approximately 11,000 ha saline soils, mainly found in four valleys (Ovche Pole, Pelagonija, Skopska and Strumica). These soils are of natural origin, but anthropogenic factors play important direct and indirect role in their genesis. The halophyte vegetation on these soils has been studied at length. This vegetation is facing great biotic interferences as a result of this some species or associations are threatened with extinction. This paper will therefore try to enlighten the current situation of this vegetation in Macedonia.