Desanka Sužnjević

Application of a Novel Antioxidative Assay in Beer Analysis and Brewing Process Monitoring

A novel antioxidative assay based on direct current polarography has been developed. Quantification of antioxidative (AO) activity has been based on a decrease of hydrogen peroxide anodic current in the presence of antioxidants. An efficient experimental procedure, without any special pretreatment of analyzed samples, has been applied. Antioxidative activity of different kinds of commercial beers (dark, blond, and alcohol-free), some small-scale made special beers with medicinal herbs and mushroom extracts, extracts themselves, as well as individual phenolic components present in beer has been measured. In addition, changes of AO activity during the full-scale industrial process of beer production have been monitored. A strong correlation between results obtained and total phenolics content has been observed. The assay can be recommended for application in brewing industry, either to survey a process with the aim to optimize relevant technological factors or to analyze quality of final product.

Antioxidant activity of wines determined by a polarographic assay based on hydrogen peroxide scavenge.

Antioxidant (AO) activity of various red and white wines of different origin as well as some individual phenolic compounds present in wine has been assessed using a polarographic assay. Direct current polarography has been used to survey hydrogen peroxide scavenge (HPS) upon gradual addition of tested samples. Results expressed as reciprocal value of wine volume required for 50% decrease of anodic limiting current of hydrogen peroxide have been validated through correlation with Folin-Ciocalteau and DPPH assays. All wines exhibit HPS activity analogous with total phenolic content and DPPH scavenge. Reliability and accuracy, low cost, and rapid and direct experimental procedure open a wide area for application of this assay, making it a good alternative to standard, widely accepted AO assays.

Polarographic study of hydrogen peroxide anodic current and its application to antioxidant activity determination.

Behavior of hydrogen peroxide in alkaline medium has been studied by direct current (DC) polarography with dropping mercury electrode (DME) aiming to apply it in antioxidant (AO) activity determination. Development of a peroxide anodic current having form of a peak, instead of common polarographic wave, has been investigated. As a base for this investigation the interaction of H(2)O(2) with anodically dissolved mercury was followed. Formation of mercury complex [Hg(O(2)H)(OH)] has been confirmed. The relevant experimental conditions, such as temperature, concentration and pH dependence, as well as time stability of hydrogen peroxide anodic current, have been assessed. Development of an AO assay based on decrease of anodic current of hydrogen peroxide in the presence of antioxidants (AOs) has been described. Under optimized working conditions, a series of benzoic acids along with corresponding cinnamate analogues have been tested for hydrogen peroxide scavenging activity. In addition, the assay versatility has been confirmed on various complex samples.

Changes of hydrogen peroxide and radical-scavenging activity of raspberry during osmotic, convective, and freeze-drying.

This study was conducted to investigate the influence of different drying treatments on antioxidant (AO) activity and phenolic content of raspberry (Rubus idaeus), cultivar Willamette. Whole raspberry fruits were dried convectively (air-drying), osmotically, and freeze-dried. Acetone-water extracts of fresh and dried raspberries were assessed for total phenolic content by standard Folin-Ciocalteau method. Two AO assays were applied, a recently developed direct current (DC) polarographic assay based on decrease of anodic oxidation current of hydrogen peroxide and widely used radical scavenge against the 1,1-diphenyl-2-picrylhydrazyl (DPPH). Strong correlation has been obtained between both AO assays and total phenolic content. In addition, some individual phenolic compounds present in raspberry have been assessed using DPPH and DC polarographic assay. Comparison and evaluation of drying methods has been based on preservation of AO activity and total phenolic content. Obtained results confirmed superiority of freeze-drying; convective drying caused slight changes while osmotic dehydration showed a significant decrease of phenolic compounds and AO activity.

Antioxidant activity of propolis extracts from Serbia: A polarographic approach

Antioxidant activity (AO) of commercial propolis extracts (PEs), available on Serbian market, was determined by direct current (DC) polarography. Polarographic anodic current of 5.0 mmol L(-1) alkaline solution of H2O2 was recorded at potentials of mercury dissolution. Decrease of the current was plotted against the volume of gradually added PEs. The volume of PE causing 20% current decrease was determined from the linear part of the plot. Antioxidant activity was expressed in H2O2 equivalent (HPEq), representing the volume of PE that corresponds to 1.0 mmol L(-1) H2O2 decrease. Resulting HPEq ranged between 1.71±0.11 and 8.00±0.18 μL. Range of 1,1-diphenyl-2-picryl hydrazyl (DPPH) radical scavenging activity was from 0.093±0.004% to 0.346±0.006%. Total phenolic content (TCP) of PE with superior AO activity was 5.31±0.05% g GAE, while the extract with the lowest activity contained 1.45±0.02% g GAE. Antioxidant activity, determined by polarographic method, was correlated with DPPH scavenging activity (R2=0.991) and TCP (R2=0.985). Validity of obtained results was further confirmed using ANOVA and post hoc Tukey HSD test.

Electrochemical versus spectrophotometric assessment of antioxidant activity of hop (Humulus lupulus L.) products and individual compounds.

Antioxidant (AO) activity of extracts of hop cones (Serbian domestic varieties) and commercial hop products (Saaz, Spalter, Spalter select, and Magnum pellets) was determined by parallel application of recently developed direct current (DC) polarographic and widely used DPPH assay. Correlations between 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) scavenging and total phenolics (TPC) determined by the Folin-Ciocalteu assay (FC) (0.99), and between H2O2 scavenging (HPS) and humulone content (H) determined by conductometric method (0.94), total resins (TR) (0.85), and hop storage index (HIS) (-0.90), were found statistically significant at p < 0.05 level while complete lack of HPS correlation with TPC and DPPH was observed. To obtain an insight into differences between results of AO assays applied, activity of individual compounds, prevalent hop phenolics, and bitter acids was determined. By far superior HPS activity of humulone was followed by catechin, quercetin, xanthohumol, lupulone, and rutin. In contrast, DPPH scavenging activity of phenolics (quercetin > catechin > rutin > xantohumol) was found substantially higher than activity of bitter acids. According to ferric reducing antioxidant power (FRAP) and scavenging of 2,2-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS), higher AO activity was ascribed to phenolics, while almost neglecting humulone. Besides reliability, low cost, and an easy-to-handle procedure, an ability to recognize humulone as the major contributor of hop AO activity could allow DC polarographic assay to be applied in analysis of various hop-derived products.

Indirect method for quantitative determination of bovine serum albumin and transferin by anodic stripping voltammetry with a rotating glassy carbon electrode

Abstract The present study was carried out in order to investigate whether the interaction of multifunctional transport proteins, bovine serum albumin (BSA) and transferin (TF), with some metal (Me) ions, such as Hg(II) and Cu(II), in buffered solution (pH 8.0), may serve as a base for indirect quantitative determination of both proteins. For this purpose anodic stripping voltammetry with a rotating glassy carbon electrode was applied. A sufficient sensitivity on the presence of protein in solution containing Me-ions was obtained only by using a mercury dissolution signal (peak) observed at 0.1 V vs. SCE. Quantities of BSA less than 5×10−7 M were determined with a S.D.±5% (n=10) for a concentration of 3×10−7 M, and for TF the concentration less than 1.5×10−7 M could be determined with S.D.±4% (n=10) for a concentration of 1×10−7 M.

Adsorption behaviour of insulin and soybean trypsin inhibitor at the mercury ∣ solution interface

Abstract The adsorption of insulin and soybean trypsin inhibitor (STI) on the mercury electrode was investigated with phase-sensitive alternating current (ac) polarography. The investigations focused on the effect of insulin and STI concentrations on the capacitive ac component over a wide potential range at pH 8.8, when both proteins are in folded form, and at pH 1.0 when they are unfolded. Besides a pseudo-capacitance due to the faradaic process of protein –S–S– bond reduction, the presence of protein adsorption of the Frumkin type was established. From the analysis of the corresponding adsorption isotherms, the relevant thermodynamic adsorption parameters were determined. Similarities in the adsorption characteristics of both proteins studied were demonstrated, and the differences in the adsorption behaviour between native and denatured proteins were proven. The data obtained is also discussed from the aspect of protein disulphide bond interaction with mercury.

Differential Pulse Polarographic Investigation of Copper (II) - Cephalexin Complex

Abstract It has been found by dp polarography that cephalexin forms a complex Cu(CEF)2, at pH = 8.7, ionic strength μ = 0.2 and room temperature. The stoichiometric ratio and stability constant values have been evaluated by Linganes and De Ford and Humes methods. The overall stability constants, logβ2 = 9.44 and 9.13, have been determined with methods applied.

Pulse polarography of soybean trypsin inhibitor in the presence of dithiothreitol

Abstract The redox system of reduced and oxidized dithiothreitol, DTT(SH) 2 /DTT(S-S), was followed in the presence of bovine pancreatic trypsin inhibitor (BPTI) from buffer solution pH 8.8 using differential pulse polarography (DPP). The reduction of -S-S- bonds in protein with DTT(SH) 2 was investigated either in absence or in the presence of denaturant such as guanidine hydrochloride (Gdn-HCl). From the analysis of -SH and -S-S- DPP peak current intensities, the kinetic of BPTI unfolding was estimated. It was found that the reaction rate is one order of magnitude higher when denaturant is present, indicating that the lifetime of the corresponding intermediary is shortened.