N. Vivas

Free radical scavenging effect of anthocyanins in red wines

Free radicals are extremely harmful to living organisms in that, they attack different constituents of the cell, leading to acceleration of the ageing process and sometimes even its destruction, or if the DNA is affected, irreversible malfunctions. It is now widely recognised that the phenolic compounds of wine have very high free radical scavenging potential. The aim of this paper is to determine which of these phenolic compounds are responsible for the strong free radical scavenging potential of red wines. In order to do so, a red wine was fractionated into phenolic fractions. After extraction and purification of these compounds from the wine, we have measured their free radical scavenging activities using an enzymatic method. The anthocyanic fraction showed a high free radical scavenging power in relation to the other tannic fractions. In order to explain this phenomenon, some pure anthocyanins were studied and a relationship between their free radical scavenging activity and their molecular structure was suggested.

The influence of various phenolic compounds on scavenging activity assessed by an enzymatic method

The effect of pure monomeric and dimeric procyanidins on superoxide anion radicals (O2°−) was studied with an enzymatic method and their IC50 was determined. A comparative study of the results suggested that the antiradical potential of these phenolic compounds closely depends on their stereochemical structure. Modification of the chiral carbon, C3 involved in the oxidation mechanism induces differences in the scavenging action of (+)-catechin (2R : 3S) or (−)-epicatechin (2R : 3R). The stereochemical conformation of the interflavan linkage (axial or pseudo) according to the chemical nature of dimeric procyanidin units also influences the radical oxidation mechanism. The nature of the interflavan linkage between the two units in dimeric procyanidins (C4–C8 or C4–C6 linkage) is an important factor responsible for effectiveness of the behaviour polyphenols towards O2°−. The extraction of oligomeric procyanidins in grape seeds enabled us to study the effect of polymerisation and galloylation on their scavenging activities. The results clearly showed that the molecular scavenging mechanism of these molecules is closely connected with their spatial conformation. © 1999 Society of Chemical Industry

Determination of the Composition of Commercial Tannin Extracts by Liquid Secondary Ion Mass Spectrometry (LSIMS)

The composition of various commercial tannin extracts were determined by liquid secondary ion mass spectrometry (LSIMS). Spectra were obtained directly from tannin extracts without any pre-separation. Eight different tannin powders were analysed : three gallotannins (Chinese, Turkish, tara), three ellagitannins (sweet chestnut, pendunculata oak, sessile oak), one mixed hydrolysable tannin (myrabolans) and one proanthocyanidin (grape seeds). This method enabled the main molecules in these powders to be identified.

Structure simulation of two ellagitannins from Quercus robur L.

Abstract Two major ellagitannins from Quercus robur , vescalagin and castalagin, were studied by 1 HNMR and LSI-mass spectrometry, and molecular mechanics. A plausible 3D-structure is proposed for each of the two diastereoisomers. These structures were the most stable ones found after a conformational analysis study and their calculated NMR spectra are in good accordance with measured ones.

A complete structural and conformational investigation of procyanidin A2 dimer

Abstract Structural and conformational study of A2 procyanidin is presented. By using NMR and molecular mechanics. A demonstration of the C4–C8 bond and of an additional C2-O-C7 ether linkage, characteristics of the procyanidin of A-series, was achieved.

Influence of oak wood and grape tannins on the lactic acid bacterium Œnococcus œni (Leuconostoc oenos, 8413)

Grape tannins, procyanidins, and oak wood tannins, ellagitannins, do not have the same effect on Œnococcus œni. Oligomer procyanidins which are extracted from grape seeds are powerful inhibitors, affecting bacterial viability in non-growing conditions, bacterial growth and malolactic activity. Pure ellagitannins on the contrary appear to be propitious to the viability of Œ œni, while the total oak extract is also a powerful inhibitor. We demonstrate that ellagitannins when oxidised have a strong inhibiting effect, as opposed to procyanidins which lose all effect when oxidised. One of the mechanisms involved may be compared to the one that occurs for medium-chain fatty acids, through adsorption on the bacterial walls.

A biochemical approach to the evolution of procyanidins in grape seeds during the ripening of red

Seed extracts of one clone of Merlot Noir were studied during maturation using low‐pressure and high‐performance liquid chromatography to observe changes in composition and to follow the evolution of the main procyanidins. These observations have prompted our laboratory to investigate the polymerisation of procyanidins associated with their extraction with an alcoholic solvent. We report the observed correlations for procyanidin dimers, which are relatively high between procyanidins B2/C1/A2 themselves (linked by C4—C8 bond), but which are non‐existent between procyanidins linked by C4—C8 and by C4—C6 bonds. These observations have enabled us to propose a hypothesis regarding procyanidin oligomer biosynthesis.

Isolation and structural characterization of anthocyanin-furfuryl pigments.

Condensation reactions of malvidin-3-glucoside with two representative oak wood furanic aldehydes (furfural and methylfurfural) were conducted in wine-like model solutions. Methylfurfural led to the formation of malvidin-3-glucoside-methylfurfural (603 m/z), whereas furfural led to the formation of malvidin-3-glucoside-furfural (589 m/z). The latter was structurally characterized by 1D and 2D NMR, allowing an elucidation of the formation mechanism of these anthocyanin-furanic aldehyde adducts in the absence of flavanols.

Formation of Flavanol-aldehyde Adducts in Barrel-aged White Wine – Possible Contribution of These Products to Colour

This paper describes the formation and diversity of new compounds resulting from the polymerisation of furanic and phenolic flavanol-aldehydes with HPLC‑DAD and LC‑ES/MS analysis. Polymerisation, resulting from nucleophilic reactions, formed dimers, trimers, soluble and insoluble polymers. Reactions in hydroalcoholic solution with pure aldehydes (phenolic and furanic) and flavanols (catechin) were studied. The study was repeated with different aldehydes in white wine. This research focused particularly on the colour properties of the released products and their potential impact on the colour of white wine. Some products were purified and isolated; these were mainly catechinfurfuraldehyde, catechin-methyl-5-furfuraldehyde, catechin-hydroxymethyl-furfuraldehyde, catechin-vanillin, and catechin-syringaldehyde dimers. The most powerful coloured products resulted from furanic aldehydes. Over the course of the experiment, the reaction produced dimers, trimers and oligomers. After 50 to 60 days, the colour of the solution was mainly due to soluble polymeric forms. In addition, the role of SO2, generally used during vinification and ageing, was studied. The influence of SO2 on the kinetics of the reaction was limited.

Purification and Partial Characterization of Melanoidins Fractions from Toasted Oak Heartwood, Comparison with Melanoidins from Roasted Coffee

During the cooking, processing, and storage of food products, a whole range of browning reactions occurs, initiated by the reaction of a carbohydrate with a compound possessing a free amino group. Melanoidins formed, influence food quality, mainly their colour, their flavour, and their antioxidant activities. Melanoidins are complex Maillard reaction products. We developed a method to isolate coffee melanoidins and melanoidins from toasted oak wood. We noted that coffee is richer in melanoidin compounds than oak wood. We presented a partial characterization of melanoidins fractions from toasted oak heartwood, and a comparison with melanoidins from roasted coffee. Mass spectra of the fractions isolated from toasted oak wood indicate the presence of pentose and hexose-based oligosaccharides with different degrees of polymerisation. The presence of the oligosaccharide moieties, as well as their degradation products found in the oak wood melanoidins, supports the postulated carbohydrate-based origin of melanoidins.