Julián C. Rivas-Gonzalo

Evaluation of the antioxidant properties of fruits

Abstract Twenty-eight different fruits were analysed for antioxidant activities using two different methods, one that determines the inhibition of ascorbate/iron-induced peroxidation of phosphatidylcholine, by means of thiobarbituric acid-reactive substances (TBARS) measurement, and another that evaluates the scavenging of the radical cation of 2,2′-azinobis (3-ethyl-benzothiazoline-6-sulphonate) (ABTS) relative to Trolox C, a water-soluble vitamin E analogue. The values of the antioxidant capacities of the analysed fruits were in a wide range from 50 g to more than 5 mg for the IW 50 (dry weight causing 50% inhibition of lipidic peroxidation) and from it 406 μmol/g for the TEAC (μmol Trolox equivalents g −1 ). There was no significant correlation between antioxidant activity (IW 50 and TEAC) and the contents of flavanol of the samples. The antioxidant activities of the analysed fruits cannot only be attributed to their flavanol contents, but to the result of the action of different antioxidant compounds present in the fruits and to possible synergic and antagonist effects still unknown.

Chromatic characterization of anthocyanins from red grapes-I. pH effect

Abstract Five anthocyanins (the 3-monoglucoside of delphinidin, cyanidin, petunidin, peonidin and malvidin), isolated from red grape skins, were subjected to a spectroscopic study to characterize their chromatic properties in a model solution imitating wine in the pH range 1.5–7.0. Tristimulus colorimetry (CIEXYZ, CIELUV and CIELAB colour spaces) proved to be a useful tool for the chromatic characterization of these anthocyanins. Significant colour differences were found among them, related to the number and type of substituents in their B rings. Two-substituted compounds were located in the area of orange hue, while three-substituted compounds were in the area of red–purple. As the methoxylation degree increased, a shift was observed toward purple. Also, a relationship was found between saturation and chroma and the number of hydroxy groups in the B ring. In all the anthocyanins studied, the increase in pH provoked a curve displacement in chromaticity, approaching that of the illuminant..

Red wine anthocyanins are rapidly absorbed in humans and affect monocyte chemoattractant protein 1 levels and antioxidant capacity of plasma

Epidemiological studies suggest that a moderate consumption of anthocyanins may be associated with protection against coronary heart disease. The main dietary sources of anthocyanins include red-coloured fruits and red wine. Although dietary anthocyanins comprise a diverse mixture of molecules, little is known how structural diversity relates to their bioavailability and biological function. The aim of the present study was to evaluate the absorption and metabolism of the 3-monoglucosides of delphinidin, cyanidin, petunidin, peonidin and malvidin in humans and to examine both the effect of consuming a red wine extract on plasma antioxidant status and on monocyte chemoattractant protein 1 production in healthy human subjects. After a 12-h overnight fast, seven healthy volunteers received 12 g of an anthocyanin extract and provided 13 blood samples in the 24 h following the test meal. Furthermore, urine was collected during this 24-h period. Anthocyanins were detected in their intact form in both plasma and urine samples. Other anthocyanin metabolites could also be detected in plasma and urine and were identified as glucuronides of peonidin and malvidin. Anthocyanins and their metabolites appeared in plasma about 30 min after ingestion of the test meal and reached their maximum value around 1.6 h later for glucosides and 2.5 h for glucuronides. Total urinary excretion of red wine anthocyanins was 0.05+/-0.01% of the administered dose within 24 h. About 94% of the excreted anthocyanins was found in urine within 6 h. In spite of the low concentration of anthocyanins found in plasma, an increase in the antioxidant capacity and a decrease in MCP-1 circulating levels in plasma were observed.

Structural diversity of anthocyanin-derived pigments in port wines

Abstract One year-old Port wine made from grapes of the Douro Valley was analysed for its anthocyanin-like pigment composition. The samples were purified by low pressure Toyopearl gel column chromatography, yielding two fractions. Fraction A was eluted with water/methanol 20% (v/v) and fraction B was eluted with methanol 100% (v/v). Structural elucidation of the pigments detected was attempted using LC/DAD-MS. Several anthocyanin-derived pigments were detected. Fraction A was mainly comprised of malvidin 3-glucoside and its pyruvic acid adducts. Additionally, other minor anthocyanin-pyruvic acid derivatives were also detected. Fraction B was shown to contain three groups of anthocyanin-derived pigments: (1) pigments in which anthocyanins are linked to a catechin unit via an ethyl linkage; (2) pigments in which anthocyanins are linked to a catechin unit or a procyanidin dimer via a vinyl linkage; (3) pigments in which anthocyanins are linked to a 4-vinylphenol group. The UV-visible spectral characteristics of most of these pigments show that they are contributing to the changing colour of Port wine from purple-red to a more orange-red hue.

Interactions between catechin and malvidin-3-monoglucoside in model solutions

The interaction between (+)-catechin and malvidin-3-monoglucoside was studied in model solutions at pH values of 3.2 and 4 over a 30-day period at 32 °C. With time, a progressive browning, accompanied by a hypso-chromic shift in their visible absorption maxima, was observed in the solutions. This was attributed to the formation of yellow pigments showing spectra with absorption maxima ranging between 425 nm and 455 nm, as detected by HPLC/DAS. A mechanism is proposed for the formation of these pigments, according to which the anthocyanin in flavylium form would bind through its C-4 to C-8 of catechin to give a colourless condensed flavene, which through an oxidative mechanism would later become rearranged to a xanthylium-like derivative. A degradation process of the anthocyanin was seen to overlap that of condensation. Syringic acid was detected as being released from the anthocyanin degradation. When the solutions were conserved at 15 °C, all the processes were reduced and minor modifications occurred during the assay period.

Formation of anthocyanin-derived pigments in experimental red wines / Formación de pigmentos derivados de antocianos en vinos tintos experimentales

Red wines obtained by microvinification in the laboratory and adjusted to three pH values (3.2, 3.6 and 4.0) were examined for the formation of anthocyanin-derived pigments throughout nine months of storage in bottles at 15 °C. The formation of the pigments was also followed in aliquots of the wines at pH 3.2 with added acetaldehyde (800 mg/L). Pigment analyses were accomplished by HPLC using double on-line detection by diode array spectrophotometry and mass spectrometry. Two dif ferent types of pigments were observed. The first were products derived from the condensation be tween anthocyanins and flavanols by ethyl bridges. The second corresponded to products showing an additional heterocycle in the anthocyanin structure (vitisin-like pigments); of these, vitisin B, which derives from malvidin 3-monoglucoside, was the most important one. Products similar to vitisin B derived from other anthocyanins were also detected, as well as structurally related pigments con taining flavanol moieties. The formation of all these pigments involves the acetaldehyde, since they appeared or were enhanced as a result of its addition, and were also favored in more acidic wines.

Polyphenolic, polysaccharide and oligosaccharide composition of Tempranillo red wines and their relationship with the perceived astringency

The influence of the proanthocyanidic, polysaccharide and oligosaccharide composition on astringency perception of Tempranillo wines has been evaluated. Statistical analyses revealed the existence of relationships between chemical composition and perceived astringency. Proanthocyanidic subunit distribution had the strongest contribution to the multiple linear regression (MLR) model. Polysaccharide families showed clear opposition to astringency perception according to principal component analysis (PCA) results, being stronger for mannoproteins and rhamnogalacturonan-II (RG-II), but only Polysaccharides Rich in Arabinose and Galactose (PRAGs) were considered in the final fitted MLR model, which explained 96.8% of the variability observed in the data. Oligosaccharides did not show a clear opposition, revealing that structure and size of carbohydrates are important for astringency perception. Mannose and galactose residues in the oligosaccharide fraction are positively related to astringency perception, probably because its presence is consequence of the degradation of polysaccharides.

Statistical correlation between flavanolic composition, colour and sensorial parameters in grape seed during ripening.

The aim of this work has been to determine the correlations between sensory analysis, colour and content of main flavanols present in seeds. For this, the flavanic composition of grape seeds with different degrees of maturity was analysed by HPLC-DAD-MS and the obtained results were correlated with CIELab colour parameters, perceived colour (C), hardness of the seed (HS), tannic intensity (TI) and astringency (A). Multiple linear regression analysis (MLR) with the variables showing significant correlations (p<0.05) was also performed. Grape seeds undergo important decreases in the content of catechins and procyanidin oligomers during ripening. Epicatechin-(4-8)-epicatechin-3-O-gallate (B2G) and (-)-epicatechin-3-O-gallate (ECG) are the flavanolic compounds whose contents decrease most. The changes in the phenolic composition accompany changes in TI, A and HS. The total content of flavanols in the seed is not the only factor affecting these attributes, since samples containing higher contents in flavanols can exhibit less astringency and tannic intensity than others with lower ones. The qualitative profile of the seeds is, therefore, also responsible for the sensations elicited in the mouth. A and HS parameters are more affected by the presence of galloylated dimeric procyanidins in the molecule than TI. CIELab colour parameters of seeds have high correlation coefficients with many flavanolic compounds. ECG was the compound most related to these parameters.

Relationship between the sensory-determined astringency and the flavanolic composition of red wines.

The relationship between the proanthocyanidin profile and the perceived astringency was assessed in 13 commercial Tempranillo red wines. The concentration and compositional information were obtained by liquid chromatography with diode array detection coupled to electrospray ionization mass spectrometry after acid-catalyzed depolymerization of wine proanthocyanidins in the presence of excess phloroglucinol. Statistical analysis of the results showed significant correlations between sensory and chemical determinations. Astringency was more affected by the subunit composition than by the total concentration or the average degree of polymerization of wine proanthocyanidins. Higher proportions of epicatechin (EC) subunits in extension positions and gallocatechin (GC) subunits in terminal positions were shown to increase astringency. On the contrary, the amount of epigallocatechin (EGC) in both extension and terminal positions was negatively correlated with the perceived astringency.

Antioxidant properties of gallocatechin and prodelphinidins from pomegranate peel

Abstract Gallocatechins and a range of prodelphinidins were purified by high performance liquid chromatography from pomegranate peel. Gallocatechin, gallocatechin-(4-8)-catechin, gallocatechin-(4-8)-gallocatechin and catechin-(4-8)-gallocatechin were all identified, purified and quantified by LC-DAD-MS and MS-MS. The antioxidant properties of these compounds were assessed using two methods: (i) inhibition of ascorbate/iron-induced peroxidation of phosphatidylcholine liposomes; and (ii) scavenging of the radical cation of 2,2-azinobis (3-ethyl-benzothiazoline-6-sulphonate, ABTS) relative to the water-soluble vitamin E analogue Trolox C (expressed as Trolox C equivalent antioxidant capacity, TEAC). The prodelphinidin dimers were potent antioxidants in the aqueous phase, being much more effective than the gallocatechin monomer. However, in the lipid phase, only one of the dimers (gallocatechin-(4-8)-catechin) was significantly more effective than the monomer in the inhibition of lipid peroxidation of phosphatidylcholine vesicles. This study represents the first report on the antioxidant properties of prodelphinidins.