Mirjana V. Obradović

Antioxidant Capacities and Phenolic Levels of Different Varieties of Serbian White Wines

The biologically active compounds in wine, especially phenolics, are responsible for reduced risk of developing chronic diseases (cardiovascular disrease, cancer, diabetes, etc.), due to their antioxidant activities. We determined the contents of total phenolics (TP) and total flavonoids (TF) in selected Serbian white wines by colorimetric methods. Total antioxidant activity (TAA) of the white wines was analyzed using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging capacity assay. Međaš beli had the highest content of TP, TF and TAA. The radical scavenging capacity (RSC) and total antioxidant activity (TAA) of white wines were 15.30% and 1.055 mM Trolox equivalent, respectively. Total phenolic (TP) and total flavonoid (TF) contents in white wines ranged from 238.3 to 420.6 mg gallic acid equivalent per L of wines and 42.64 to 81.32 mg catechin equivalent per L of wines, respectively. A high and significant correlation between antioxidant activity and total phenolic content was determined in wines (R2 = 0.968, p < 0.01). For the individual polyphenols determination we used a high performance liquid chromatography (HPLC)-diode array detection (DAD) technique. The majority of white wine polyphenols was represent by four hydroxycinnamic acids (HCAs).

Polyphenol content and antioxidant activity of sour cherries from Serbia

The aim of this study is to evaluate the content of phenolics: the total phenols (TP), flavonoids (TF), anthocyanins (TA), as well as the total antioxidant capacity (TAC) in three sour cherry cultivars (Prunus cerasus L.) introduced to the southeast Serbia climate conditions. Among the researched sour cherries, ‘Oblacinska’ cultivar contained the highest amounts of all groups of phenolics, followed by ‘Cigancica’ > ‘Marela’. A significant difference were observed in the phenolic content among different cultivars and growing seasons (p<0.05), and the phenolic compounds were significantly higher in the growing season 2009. The examined cultivars possess a high antioxidant capacity, and all phenolics of highy correlation with TAC. The following compounds were identified and quantified using HPLC-DAD: 4 anthocyanins, the most abundant of which was cyaniding-3-glucoside in ‘Marela’ and ‘Oblacinska’, and cyanidin-3-glucosylrutinoside in ‘Cigancica’, and 4 hydroxycinnamic acids, the most abundant of which was neochlorogenic acid in all sour cherry cultivars. The growing and ripening process on the tree of sour cherry cv. Oblacinska was evaluated, also. The results showed significant increases in total phenols during the ripening, the total anthocyanins and total antioxidant capacity and 4 quantified anthocyanins, however the neochlorogenic acid decreased during the ripening. The study indicated that the growing and climate conditions in southeast Serbia are convenient for introducing sour cherry cultivars.

Catalytic determination of nanogram amounts from iron(III) using its catalytic effect on the oxidation of sodium pyrogallol-5-sulphonate by hydrogen peroxide☆

A kinetic method is described for the determination of iron(III) based on its catalytic effect on the oxidation of sodium pyrogallol-5-sulphonate by hydrogen peroxide. The reaction was followed spectrophotometrically by measuring the rate of change in the absorbance of the coloured product at 436.8 nm. Nanogram amounts of iron(III) (2.0-75.0 ng cm(-3)) can be determined with good accuracy and reproducibility. The influence of foreign ions on the results was investigated and the method was found to be adequately selective. It has been applied satisfactorily to the determination of iron(III) in tap water samples. The kinetic parameters of both the catalysed and uncatalysed reactions are reported.

Phytochemical profiles and antioxidant activities of Serbian table and wine grapes

Three table grapes and 4 wine grapes collected from a southern Serbian vineyard were evaluated and compared for their antioxidant properties and phenolic profile. Among the varieties tested, ‘Cabernet Sauvignon’ contained the highest total phenolic content with 173.6 mg/100 g of fresh weight. Also, the total flavonoid and antocyanin content of ‘Cabernet Sauvignon’ was significantly higher from the other. ‘Cabernet Sauvignon’ and ‘Merlot’ had the strongest DPPH· radicals scavenging activity (1,318.6 and 1,282.0 μmol Trolox equivalent/100 g, respectively). ‘Cabernet Sauvignon’, ‘Merlot’, ‘Prokupac’, ‘Vranac’, ‘Muscat Hamburg’, and ‘Ribier’ grape varieties were found to be rich in malvidin-3-O-glucoside, while ‘Cardinal’ grape variety was found to be rich in peonidin-3-O-glucoside. The following compounds were also identified and quantified using HPLC-DAD: 2 flavan-3-ols and 4 hydroxycinnamic acids in all grape samples. The results suggested that phytochemicals in the selected table and wine grapes have potent antioxidant activities in correlation with phenolic content.

Kinetic determination of traces of copper(II) by its catalytic effect on the oxidation of sodium pyrogallol-5-sulfonate by hydrogen peroxide

Abstract A catalytic kinetic spectrophotometric method is developed for the determination of trace amounts of Cu(II). It is based on the catalytic effect of Cu(II) on the oxidation of sodium pyrogallol‐5‐sulfonate (PS) by hydrogen peroxide in acidic madium. The reaction was monitored spectrophotometrically by measuring the increase in absorbance of the oxidation product at 436.8 nm. The optimum operating conditions regarding concentration of reagents, pH, and temperature were established. The working curve is linear in the concentration range from 10 to 300 ng cm−3 and the detection limit is 1.8 ng cm−3. The interference effect of several species was also investigated and it was found that the most common cations and anions do not interfere with the determination. The developed procedure was successfully applied to the determination of Cu(II) in water and milk.

Sulphonation of Monohydroxybenzene and Determination of the Acidity Constants of 2-Monosulphohydroxybenzene

Abstract 2-monosulphohydroxybenzene is spontaneously formed as a white deposit in a 3mol/dm3 solution of monohydroxybenzene in 96% sulphuric acid after nine days at 298K. The composition of this compound was determined by using Rasts method as well as AAS, IR and UV/VIS spectroscopy. Determination of acidity constants of 2-monosulphohydroxybenzene was done by using pH-metric and spectrophotometric titration.

Absorption spectra of the products of resorcin transformation in concentrated perchloric acid

Results of an investigation of the electronic absorption spectra of polymeric compounds spontaneously formed as a result of resorcin dissolution in 70% perchloric acid are reported. It is shown that acetone is the most convenient solvent for analytic purposes, since it allows specific detection of poly-m-phenylene oxide in a wide wavelength range.