María Teresa Escribano-Bailón

Recent advances in polyphenol research

This important book covers polyphenol chemistry, biosynthesis and genetic manipulation, ecology and plant physiology, food and nutritional aspects and the effects of polyphenols on health. Included within the contents are cutting edge chapters on biotic and abiotic stress in plants, safety and toxicity in foods, functionality and nutraceutical benefits in nutrition, and aspects of pharmaceutical and cosmetic discovery and development.

Comparative flavan-3-ol composition of seeds from different grape varieties

The flavanol composition of the seeds of 17 varieties of grape cultivated in the main wine-producing areas of Castilla-Leon (Spain) was studied. Twenty-seven different flavan-3-ols of procyanidin type were found, but no prodelphinidins were detected. Minor amounts of four hydrolyzable tannins were also present in the seed extracts of most of the grapes analyzed. All the varieties contained galloyled flavanols, such that their presence could be considered characteristic of the grape seed composition. Some proposals concerning the biosynthesis of flavan-3-ol in the grape seed are also advanced taking into account the compounds found.

Interaction of phenolic compounds with bovine serum albumin (BSA) and α-amylase and their relationship to astringency perception.

The ability of grape seed extracts to bind to bovine serum albumin (BSA) and α-amylase was studied by fluorescence quenching of protein intrinsic fluorescence and nephelometry. The influence of grape seed ripeness on astringency was also evaluated. From the spectra obtained, the modified Sterm-Volmer (K(app)) and the bimolecular quenching constants were calculated. Results showed that grape seed extracts had good affinity for proteins. The association strength of tannin-protein interactions varied with changes in tannin structure associated with the degree of ripeness affecting the binding/quenching process. In all cases studied, higher values of K(app) were obtained in samples at harvest which have greater ability to bind to proteins than have samples at post-veraison time. Nephelometric assays show the same trend as do fluorescence quenching studies. A possible explanation for this is that, as seeds ripen, their tannins increase in molecular mass, which relates to an increase in hydrophobicity of the molecules, and this increases protein affinity. However, that is contrary to the reported decrease in astringency of grape seeds during maturity. This indicates that tannin-protein interactions are not the only explanation for the complex sensations of astringency of grape seeds.

Preliminary study to determine the phenolic maturity stage of grape seeds by computer vision.

The applications of computer vision technology for acquiring and analysing images have been extended to the quality evaluation in food industry. This technique involves great advantages for the objective, rapid, non-contact and automated quality inspection and control. The aim of this work was to evaluate the potential of the computer vision to determine the phenolic maturity stage of grape seeds. Up to 21 phenolic compounds were determined by HPLC-DAD-MS in order to obtain reference values to develop the model. The CIELAB parameters, area, aspect, roundness, length, width and heterogeneity of seeds were analysed using a DigiEye(®) system. The technique reported in this work can be a good and rapid tool for taking decisions at harvest time. Notwithstanding, a comprehensive study should be made in order to develop more robust models.

New Anthocyanin-Human Salivary Protein Complexes.

The interaction between phenolic compounds and salivary proteins is considered the basis of the poorly understood phenomenon of astringency. Furthermore, this interaction is an important factor in relation to their bioavailability. In this work, interactions between anthocyanin and human salivary protein fraction were studied by mass spectrometry (MALDI-TOF-MS and FIA-ESI-MS) and saturation-transfer difference (STD) NMR spectroscopy. Anthocyanins were able to interact with saliva proteins. The dissociation constant (KD) between malvidin 3-glucoside and salivary proline-rich proteins was 1.92 mM for the hemiketal form (pH 3.4) and 1.83 mM for the flavylium cation (pH 1.0). New soluble complexes between these salivary proteins and malvidin 3-glucoside were identified for the first time.

Physico-chemical and chromatic characterization of malvidin 3-glucoside-vinylcatechol and malvidin 3-glucoside-vinylguaiacol wine pigments.

The physicochemical and chromatic features of malvidin 3-glucoside-vinylcatechol (PA1) and malvidin 3-glucoside-vinylguaiacol (PA2) adducts were investigated. Important differences between both pigments were observed. In the investigated pH range (2.0-4.5), our results suggest that PA1 could be considered as a noncovalent dimer of two pyranoflavylium ions (AH)2 which undergo a hydration reaction in two successive steps, with no proton transfer. In contrast, only proton transfer equilibrium between the pyranoflavylium ion and the quinonoid bases was observed for PA2. The hydration and acidity thermodynamic constants of both pyranoanathocyanins were determined by UV-vis spectroscopy. Pigment PA1 was shown to be less sensitive to bisulfite addition than to water addition, and PA2 seems to be largely insensitive to both water and bisulfite additions. The binding constants for the interaction between the pigments and (+)-catechin in aqueous solution and the changes in the CIELAB parameters that it provoked were also determined. The huge increase in the absorption of the pyranoflavylium ion of PA2 when it binds catechin has no equivalent for anthocyanins and nicely outlines the potential of pyranoanthocyanins in the expression of natural colors.

Multivariate analysis of sensory data of Vitis vinifera L. cv. Graciano during ripening. Correlation with the phenolic composition of the grape skins Análisis multivariante de datos sensoriales de Vitis vinifera L. cv. Graciano durante la maduración. Correlación con la composición fenólica del hollejo

El objetivo de este trabajo ha sido evaluar los cambios en los parametros sensoriales del hollejo de uva durante la maduracion y obtener una correlacion con su composicion fenolica. Se han determinado flavan-3-oles (monomeros y dimeros), prodelfinidinas, acidos hidroxibenzoicos, acidos hidroxicinamicos, antocianos y flavonoles mediante HPLC-DAD-MS. Ademas, se han evaluado los siguientes atributos sensoriales del hollejo: facilidad de dilaceracion, intensidad tanica, astringencia, acidez, sequedad, intensidad de aroma y tipo de aroma. El analisis multivariante mostro la evolucion de los hollejos a lo largo de la maduracion y la relacion entre las puntuaciones sensoriales y la composicion fenolica de los mismos. La facilidad de dilaceracion, el tipo de aroma y en menor medida la intensidad del aroma tienden a aumentar con la maduracion, pauta similar a la presentada por los compuestos fenolicos estudiados. Sin embargo, la intensidad tanica, la astringencia, la sequedad y la acidez presentan una pauta opuesta, lo que indica una disminucion de estos atributos sensoriales durante la maduracion.

The biological activity of the wine anthocyanins delphinidin and petunidin is mediated through Msn2 and Msn4 in Saccharomyces cerevisiae

Polyphenols are considered to be responsible for some of the health benefits derived from the consumption of red wine. These protective effects might probably be explained in the context of the xenohormesis theory that considers plant metabolites as interspecific chemical signals. However, the complexity of the polyphenolic constituents of different wines makes it difficult to clarify the specific contribution of polyphenols to such effects. In the present work, we fractionated the polyphenols of a red wine and evaluated the effect of each polyphenolic fraction on the growth pattern of the yeast Saccharomyces cerevisiae. We observed a different contribution of the phenolic fractions to the xenohormetic response of S. cerevisiae, the fractions that were enriched with red pigments being the most protective against oxidative insults. Moreover, we found that red wine phenolic fractions exert their biological activity through the activation of the Yap1 and Msn2 stress-responsive regulators. Above all, the anthocyanins delphinidin 3-glucoside and petunidin 3-glucoside were found to improve significantly the growth rate of S. cerevisiae in an Msn2-, Msn4-dependent manner, indicating that the stress regulators Msn2 and Msn4 participate in the xenohormetic activity of the wine polyphenols delphinidin and petunidin.

Effect of the addition of flavan-3-ols on the HPLC-DAD salivary-protein profile

The interaction between monomeric flavan-3-ols and salivary proteins has been studied using HPLC-DAD. A chromatographic method has been described and seven protein fractions were collected. The peptides and proteins present in each fraction have been identified using nLC-MS-MS analysis. The interaction between saliva and catechin, epicatechin and gallocatechin has been studied. These compounds interact in a discriminated way with salivary proteins: catechin causes a decrease of some fractions, epicatechin causes the decrease or increase of fractions while gallocatechin seems to cause an increase of two fractions. This variable behavior is explained, for the decrease in the chromatographic area, by the precipitation of salivary proteins and, for the increase of the area, by the formation of soluble complexes and/or for the formation of new peaks.

Evaluation of dihydroquercetin-3-O-glucoside from Malbec grapes as copigment of malvidin-3-O-glucoside.

Malbec is a wine grape variety of great phenolic potential characterized for its high levels of anthocyanins and dihydroflavonols. To evaluate the possible implication of dihydroflavonols in the expression of red wine color through reactions of copigmentation or condensation, assays were carried out in wine model systems with different malvidin-3-O-glucoside:dihydroquercetin-3-O-glucoside molar ratios. The addition of increasing levels of dihydroquercetin-3-O-glucoside to a constant malvidin-3-O-glucoside concentration resulted in a hyperchromic effect associated with a darkening of the anthocyanin solutions, greater quantity of color and visual saturation, perceptible to the human eye. Copigmentation and thermodynamic measurements showed that dihydroquercetin-3-O-glucoside can act as an anthocyanin copigment, similar to other usual wine components like flavanols or phenolic acids, although apparently less efficient than flavonols. The high levels of dihydroflavonols existing in Malbec wines in relation to other non-anthocyanin phenolics should make this family of compounds particularly important to explain the color expression in Malbec young red wines.