The aim of this research was to determine the total phenolic and flavonoid contents as well as to measure antioxidant activity of 24 different commercial beers consumed in Serbia.The major phenolic acids (gallic acid, protocatechuic acid, 4-hydroxybenzoic acid, 2,5- dihydroxybenzoic acid, vanillic acid, caffeic acid, syringic acid, p-coumaric acid, ferulic acid, sinapic acid, salicylic), (+)-catechin, and (-)-epicatechin were also determined by high pressure liquid chromatography method using a photodiode array detector. Gallic acid, ferulic acid, and protocatechuic acid are the most abundant phenolic acids in all samples, followed by (+)-catechin. The total phenolic content was determined using the Folin-Ciocalteu assay. The total flavonoids were measured using spectrophotometrics as the aluminum chloride assay. The results showed that the highest total phenolic and flavonoid contents were established in dark and light beer samples. 2,2-Diphenyl-1-picrylhidrazyl radical scavenging activity, 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) radical cation scavenging activity, and ferric reducing/antioxidant power were used to assess the antioxidant potential of beers. These assays, based on different chemical mechanisms, were selected to take into account the wide variety and range of action of antioxidant compounds present in selectedbeer samples. All beers showed antioxidant power, but a wide range of antioxidant capacities was observed. Statistical differences between ferric reducing-antioxidant power and the other two antioxidant capacity assays were confirmed. This study will be useful for the appraisal of phenolic profile and antioxidant activities of various beers, and it will also be of interest for people who like drinking this beverage.

No abstract

Peach (Prunus persica L.) is a fruit of high nutritional and economic value. Carbohydrates, dietary fibers, minerals and organic acids are among the major constituents of peach fruit, which contribute to the nutritional quality of both fresh fruits and juice. Polyphenolic compounds found in peach may play an important role in physiological functions related to human health. Different polyphenolics may have varied biological activities including antioxidant activity. In this study antioxidant characteristics between peel and pulp of different peach cultivars ('Radmilovčanka', 'June Gold', 'Blake', 'Hale', 'Vesna', 'Adria') and one of nectarine ('Fantasia') were investigated. The peel and pulp extracts showed a huge amount of total phenolics (TP), total flavonoids (TF), total hydroxycinnamates (TH) and total flavonols (TFL), ranging from 42.7-211.4, 11.1-128.5 mg GAE/100 g fresh weight (f.w.) (TP), 21.9-94.9, 5.0-58.9 mg CE/100 g f. . High contents of phenolic compounds were significantly correlated with high antioxidant capacities. Peach pulp and peel differ significantly in their phenolic profiles: the pulp contains mainly chlorogenic, neochlorogenic and p-coumaric acids, whereas the peel possesses chlorogenic, neochlorogenic and p-coumaric acids together with several flavonol glycosides in huge amounts. Our results indicate that cultivar and extraction solvent play important roles in phenolic compositions and antioxidant properties of peach and nectarine extracts, which was shown using statistical analysis (ANOVA). There are high correlations between extracted phenolic compounds and peach and nectarine cultivars, and used solvent and part of the fruit (peel and pulp).

The influence of solvent concentration, pH, temperature, sampler solid ratio and concentration time on the extractability of total phenolics and antioxidants from hop was investigated. The mechanism of extraction is confirmed to occur in the following steps: first, the dissolution of the phenolic compounds near the particle surface (washing) and, second, the diffusion from the solid particles to the bulk of the liquid extract (slow extraction). The process is described mathematically using two concepts of the unsteady diffusion through plant material and Ponomaryov's empirical equation. The data obtained are used to establish the kinetics and thermodynamics of the extraction process.

The influence of the solvent concentration, pH, temperature, sampler solid ratio and extraction time on the extractability of total phenolic compounds from barley was investigated. The most effective solvent (30% aqueous ethanol solution with 5% HCl v/v) was used for modeling the solid-liquid extraction of total polyphenolic compounds at the solid-liquid ratio of 30 mL/g (the ratio of the solvent volume per gram of raw material). Total phenolic compounds in the barley extracts were determined spectrophotometrically using Folin-Ciocalteu method at 760 nm. The content of the phenolic compounds of extracts depends on the extraction conditions applied. The mechanism of the extraction is confirmed to occur in the following steps: first, the dissolution of the phenolic compounds near the particle surface (washing) and second, the diffusion from the solid particles to the bulk of the liquid extract (slow extraction). The process is described mathematically using two concepts of unsteady diffusion through the plant material and Ponomaryov's empirical equations. The data obtained are used to establish the kinetics and thermodynamics of the extraction process.