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Pomegranate fruit (Punica granatum L.) is a source of numerous phenolic compounds, and it contains flavonoids such as anthocyanins, anthocyanidins, cyanidins, catechins and other complexes of flavonoids, ellagitannins, and hydrolyzed tannins. Pomegranate juice shows antioxidant, antiproliferative, and anti-atherosclerotic properties. The antioxidant capacity (TEAC) of the pomegranate juices was measured using electron paramagnetic resonance (EPR) spectroscopy and 1,1-diphenyl-2-picrylhydrazyl (DPPH•) as a source of free radicals, and the total phenolic (TP) content was measured using UV-Vis spectroscopy. All the examined pomegranate juices exhibited relatively high antioxidant properties. The TEAC values determined by means of EPR spectroscopy using Trolox (TE) as a free radical scavenger were in the range of 463.12 to 1911.91 μmol TE/100 mL juice. The TP content measured by the Folin-Ciocalteu method, using gallic acid (GA) as a free radical scavenger, widely varied in the investigated pomegranate juice samples and ranged from 1673.62 to 5263.87 mg GA/1 L juice. The strongest antioxidant properties were observed with the fresh pomegranate juices obtained from the fruits originating from Israel, Lebanon, and Azerbaijan. Correlation analysis of numerical data obtained by means of EPR spectroscopy (TEAC) and UV-Vis spectroscopy (TP) gave correlation coefficient (r)=0.90 and determination coefficient (r2)=0.81 (P<0.05).

This study presents the results of comparative evaluation of the antioxidant activity of the phenolic fraction exhaustively extracted with aqueous methanol from 18 different thyme (Thymus L.) specimens and species. This evaluation is made with use of the same free radical source (DPPH• radical), three different free radical scavenging models (gallic acid, ascorbic acid, and Trolox), and three different measuring techniques (the dot blot test, UV-Vis spectrophotometry, and electron paramagnetic resonance spectroscopy, EPR). A comparison of the equivalence of these three different measuring techniques (performed with use of hierarchical clustering with Euclidean distance as a similarity measure and Ward's linkage) is particularly important in view of the fact that different laboratories use different antioxidant activity measuring techniques, which makes any interlaboratory comparison hardly possible. The results obtained confirm a semiquantitative equivalence among the three compared methodologies, and a proposal is made of a simple and cost-effective dot blot test that uses the DPPH• radical and provides differentiation of antioxidant activity of herbal matter comparable with the results of the UV-Vis spectrophotometry and EPR.

Fruit preparations (e.g., fruit juices and nectars) are rich in plant pigments and of great demand by the alimentary and pharmaceutical industry, basically not only due to their health-enhancing properties, but also due to their attractive colors and an overall high esthetic valor. Anthocyanins and anthocyanidins are an interesting group of plant pigments, and in this study, a thin-layer chromatographic detection was carried out of two anthocyanins (cyanin and keracyanin) and two anthocyanidins (pelargonidin and delphinidin) in a selection of the commercial and homemade fruit juices and the infusions prepared of dried plants. Moreover, the same preparations were evaluated for their antioxidant properties by means of two spectrophotometric methods (based on the 2,2′-azino-di-[3-ethylbenzthiazoline] sulfonate (ABTS) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) tests, respectively) and by the dot-blot test (based on DPPH). Finally, an effort was undertaken to correlate the chromatographically established occurrence of plant pigments in the investigated fruit preparations with their antioxidant properties. However, this correlation was not straightforward, and for at least two reasons. First, the four plant pigments considered are not the only secondary plant metabolites which exert an antioxidant activity. Second, different chemistries stand behind the two spectrophotometric antioxidant activity tests (ABTS vs. DPPH), and the different measuring techniques (spectrophotometry vs. dot blot) are assumed. Nevertheless, it was established that the juices and infusions with the highest detected numbers of plant pigments characterize with the high antioxidant activities also (with blueberries, chokeberries, and hibiscus flower on the top positions). In that way, confirmation of the antioxidant potential of the plant pigments was obtained. Moreover, the presence of certain plant pigments in fruit juices and plant infusions was reported for the first time. [ABSTRACT FROM PUBLISHER]