Blaga Radovanovic

Characterization and antimicrobial activity of the bioactive metabolites in streptomycete isolates

Twenty different streptomycete isolates were obtained from soils of southeast Serbia. Five isolates identified as Streptomyces hygroscopicus (SH100, SH101, SH102, SH103, and SH104) showed strong activity against Botrytis cinerea, a parasite found in domestic vines. These isolates were extensively studied for their in vitro antimicrobial activity against Gram-positive bacteria, Gram-negative bacteria, yeasts and fungi, and also antiviral activity against Herpes simplex. The results indicated that the obtained isolates were highly active against Botrytis cinerea, Candida albicans, and Herpes simplex, with an inhibition zone at ≥31 mm. The structure of the bioactive components was determined using elemental analysis, as well as UV/VIS, FTIR, and TLC.

Free radical scavenging activity and anthocyanin profile of Cabernet Sauvignon wines from the Balkan region.

The present study is focused on anthocyanin derivatives characterizing the antioxidant activity of Cabernet Sauvignon wines produced from different vineyard regions in the Balkans. These bioactive compounds were quantified with a high performance liquid chromatography (HPLC)-diode array detection (DAD) method. The antiradical activity was estimated by the ability of the wine to scavenge the stable 2,2`-diphenyl-1-picrylhydrazyl free radical (DPPH•). The results show that the total anthocyanin content varied from 205.88 to 1940.28 mg/L, depending on agroclimatic factors and the enological practices of the corresponding vineyard region. The most prominent antocyanin in all investigated Cabernet Sauvignon wines was malvidin-3-O-monoglucoside, which accounted for 50.57% of total content, followed by its acetyl derivatives, 15.45%, and p-coumaryl derivatives 5.66%. The relationship between the anthocyanin derivatives and free radical scavenging activity is discussed. A high correlation between total anthocyanin content and DPPH· scavenging ability of tested wines was confirmed (r2 = 0.9619). The significant correlations were obtained between antiradical activity and the sum of 3-monoglucoside (r2 = 0.95594), the sum of 3-acetyl-3-glucoside (r2 = 0.9728) and the sum of p-coumaryl-3-glucoside (r2 = 0.8873) of wine samples. It can be concluded that, the anthocyanin composition can be used as biochemical marker for the authenticity of red grape cultivar and their corresponding single-cultivar wine.

Changes in polyphenolic content and antioxidant activity of grapes cv Vranac during ripening.

This study characterised and evaluated the phenolic composition and antioxidant activity of the red wine grape Vranac (Vitis vinifera L.) from the southern Serbian vineyard region during grape ripening. Polyphenol composition at different harvest dates was determined by HPLC-DAD analysis. Antioxidant activity was estimated by DPPH assay. The study demonstrates that the Vranac variety represents important sources of dietary antioxidants. The results show that (+)-catechin, (-)-epicatechin and procyanidin dimer B2 were the most prevalent in the seeds, and quercetin and malvidin glucosides in the grape skins. All grape extracts were shown to have high radical-scavenging activity. Strong correlations between radical-scavenging activity and polyphenols suggest that the phenolic composition of the Vranac variety contributes significantly to the antioxidant capacities of grape extracts. During grape ripening there were significant changes in physiological properties and phenolic content, and it is important to determine optimal harvest time, which will ensure grapes with very good quality parameters (in our study at the 30th day after veraison).

The Effect of Accelerators on Curing Characteristics and Properties of Natural Rubber/Chlorosulphonated Polyethylene Rubber Blend

The aim of this work was to determine the influence of accelerator type on curing behavior and properties of sulphur vulcanized rubber blend based on natural rubber (NR) and chlorosulphonated polyethylene (CSM). In NR/CSM compounds filled with carbon black three types of accelerator were used: N-cyclohexylbenzothiazylsulphenamide (CBS), tetramethylthiuram disulphide (TMTD), and 2-mercaptobenzothiazol (MBT). The curing characteristics were estimated using oscillating disk rheometer. The results revealed that the accelerator type not only affects the cure characteristics, but also has great influence on the mechanical properties of obtained elastomers. It was determined that the tensile strength of rubber blends cured in the presence of TMTD was relatively high.

Phenol composition, DPPH radical scavenging and antimicrobial activity of cornelian cherry (Cornus mas) fruit and leaf extracts

Fruit is rich in different phenolic compounds which are recognized as potential natural medicaments and have been used in folk medicine for centuries. In order to evaluate phenol composition, cornelian cherry (Cornus mas) fruit and leaf extracts were subjected to the spectrophotometric and HPLC analysis. The radical scavenging activity was estimated using DPPH test and antimicrobial activity by disc diffusion and microwell dilution tests. All extracts showed high phenol content from 89.89 ± 0.45 to 117.34 ± 1.40 mg f gallic acid equivalents GAE/g extract dry matter DM but different composition of phenol compounds. Flavonols, anthocyanins, flavan-3-ols and phenolic acids were the main phenol classes found in the investigated fruit and leaf extracts. All extracts showed significant radical scavenging activity and a correlation with total phenol content (R2 = 0.9832). Significant antimicrobial activity was found against Gram-positive, followed by Gram-negative strains, and yeast in all tested extracts. Cornelian cherry fruit and leaf extracts, rich in phenolic content, with significant antiradical and antimicrobial activity, can be used as additives in food and medicaments. [Projekat Ministarstva nauke Republike Srbije, br. 34012, br. 31020 and br 176006 and EU, FP7 - Regpot - 2007- 3-01, the project «Chromlab-Antioxidant», No. 204756]

Phenolic Compounds and Bioactivity of Healthy and Infected Grapevine Leaf Extracts from Red Varieties Merlot and Vranac ( Vitis vinifera L.)

We investigated the phenolic composition, radical scavenging activity, and antimicrobial activity of grapevine leaf extracts from two red grape varieties, Vranac and Merlot (Vitis vinifera L.). The extracts were prepared from healthy grapevine leaves and those infected by Plasmopara viticola (downy mildew). The phenolic composition of the grapevine leaf extracts was determined using spectrophotometric assays and reverse-phase high performance liquid chromatography (RP-HPLC). The radical scavenging activity of grapevine leaf extracts was determined by the 2,2-diphenyl-1-picrylhydrazyl assay, and their antimicrobial activity was determined by microwell dilution tests. The total phenolic content was higher in healthy grapevine leaf extracts than in infected grapevine leaf extracts. The RP-HPLC analysis detected significant amounts of flavonols, phenolic acids, and flavan-3-ols, and small amounts of stilbenes in the grapevine leaf extracts. Compared with the infected grapevine leaf extracts, the healthy grapevine leaf extracts were richer in flavonols, phenolic acids, and flavan-3-ols, but had lower stilbenes contents. All extracts showed strong free radical scavenging activity, which was strongly correlated with the total phenolic content (R2 = 0.978). The extracts showed a stronger antimicrobial activity towards Gram-positive bacterial strains than towards Gram-negative bacterial strains and yeast. The phenolic compounds in grapevine leaves were responsible for their strong radical scavenging and antimicrobial activities. Together, these results demonstrate that grapevine leaves have high nutritional value and can be used as a fresh food and to prepare extracts that can be used as additives in food and medicines.

Spectroscopic and thermodynamic studies of complexation of some divalent metal ions with isatin-β-thiosemicarbazone

Metal complexes of some divalent metal ions (Co, Ni, Cu, Zn, Hg, and Pd) with isatin-β-thiosemicarbazone (ITS) as the Schiff base have been investigated potentiometrically and spectrophotometrically. The dissociation constants of the ligand and formation constants of the metal complexes, as well as the corresponding thermodynamic functions (ΔG, ΔH and ΔS) have been determined at different temperatures in ethanol—water solution. The full stability constants were also evaluated spectrophotometrically by the Job method. The experimental results indicate that Cu(II), Zn(II), Pd(II), and Hg(II) form one-to-one molecular complexes (ML) with the studied ligand, whereas Co(II) and Ni(II) form both ML and ML2 species.

Phenolic compounds and biological activity of Capsicum annuum L.

The objective of this study was to evaluate antifungal and antioxidant activities of vegetable extracts ( Capsicum annuum L. cv. Dora, cv. Strizanka, cv. Morava), grown in Serbia. Different experimental models have included the determination content of total phenolics, total flavonoids, antioxidant capacity and minimum inhibitory concentration of the extract. The phenolic composition of different extracts was determined by the high-performance liquid chromatography (HPLC) method. The highest amounts of phenols and highest antioxidant capacity were found in the cultivar Dora extracts. The highest phenolic content has been shown in cultivar Strizanka ethanol extract. All of the extracts showed strong antimicrobial activity. On the basis of the results obtained, the extracts were found to serve as a potential source of natural antioxidants and antimicrobial due to their marked activity. The obtained results may be useful in the evaluation of new dietary and food products. Key words: High-performance liquid chromatography (HPLC), phenolic components, antimicrobial activity, antioxidant activity.