Antioxidant efficiency of polyphenols from coffee and coffee substitutes-electrochemical versus spectrophotometric approach.

Antioxidant (AO) capacity of instant, espresso, filter and Turkish/Greek coffee brews, coffee substitutes (roasted chicory root, barley, pea, chickpea, carob and dried fig) and individual compounds (phenolic acids, flavonoids, methylxanthines, N-methyl pyridinium and HMW melanoidins) was assessed using DC polarographic assay based on decrease of anodic current originating from hydroxo-perhydroxo mercury complex formed in alkaline solutions of H2O2 at potential of mercury dissolution, as well as three spectrophotometric assays (DPPH, ABTS and FRAP). A large difference between applied assays ability to recognize various types of individual AOs was noticed. Only according to DC polarographic assay significant AO activity was ascribed to methylxanthines and N-methyl pyridinum. The total content of phenolics (TPC) present in complex samples was determined by FC assay. The highest TPC was ascribed to instant coffees and coffee substitutes while the lowest to decaffeinated filter coffee. Complex samples were grouped based on principal components analysis, phenolics AO coefficient, calculated as the ratio between AO capacity and TPC, and relative AO capacity index (RACI), calculated by assigning equal weight to all applied assays including FC. The highest values of RACI were ascribed to instant coffee brews, followed by substitutes while the lowest to the decaffeinated espresso coffee.

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.

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.

Polarographic assay based on hydrogen peroxide scavenging in determination of antioxidant activity of strong alcohol beverages.

Total antioxidant (AO) activity of strong alcohol beverages such as wine and plum brandies, whiskeys, herbal and sweet fruit liqueurs have been assessed using a polarographic assay based on hydrogen peroxide scavenging (HPS). Rank of order of total AO activity, expressed as percentage of decrease of anodic oxidation current of hydrogen peroxide, was found analogous with total phenolic content estimated by Folin-Ciocalteau (FC) assay and radical scavenging capacity against the stable free radical 1,1-diphenyl-2-picrylhydrazyl (DPPH). Application of the assay for surveying of a quarter century long maturation of plum brandy in oak barrel was demonstrated. In addition, influence of different storage conditions on preservation of AO activity of some herbal liqueurs was surveyed. Wide area of application of this simple, fast, low cost and reliable assay in analysis and quality monitoring of various strong alcohol beverages was confirmed.

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.

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.