Johanna Bakker

Identification of an anthocyanin occurring in some red wines

Abstract An anthocyanin-type pigment, vitisin A, was found in small amounts in some red wines and at trace levels in stored grapes. HPLC and spectrophotometric analysis showed that vitisin A exhibited a unique UV-Vis spectrum. Vitisin A was isolated, purified and identified using FAB mass spectrometry and NMR. The aglycone, vitisidin A, is 68 mass units greater than malvidin, accounted for by an additional C 3 O 2 substituent. Further accurate mass determinations and NMR studies of both malvidin 3-glucoside and vitisin A confirmed that vitisin A is based on malvidin 3-glucoside with an additional C 3 O 2 between position 4 and the 5-hydroxyl of the molecule. Five different isomers were distinguished by NMR, namely the flavylium cation, quinonoidal base, chalcone form and two carbinol pseudobases. The assignment of one of the protons remains tentative due to the rapid hydrogen/deuterium exchange. The structure was determined to be 3-formyl-4- d -β-glucopyranosyloxy-8-hydroxy-5-(4-hydroxy-3,5-dimethoxy)phenyl-2-oxo-1,6-dioxa-2,3-dihydrophenalene.

Correlations between saliva protein composition and some T–I parameters of astringency

Abstract Saliva samples were collected from 12 panellists immediately before and after the sensory assessment of two red wine samples and the salivary proteins in all samples were analysed by high performance liquid chromatography (HPLC). Three peaks appeared in the majority of the chromatograms and the areas of these peaks were individually correlated for each assessor against four astringency time–intensity (T–I) parameters (time to maximum intensity, total duration, maximum intensity and area under the T–I curve). Astringency was not correlated with the total area in the saliva chromatograms. However, statistically significant correlations were obtained between the area of particular proteins and the sensory data indicating that the concentration of individual proteins in saliva might be more important for astringency than the total protein content. Significant correlations were also obtained between the relative concentration of individual proteins and the T–I data.

Effect of sulphur dioxide and must extraction on colour, phenolic composition and sensory quality of red table wine

Red wines were made during 1992 from Vitis vinifera var Roriz grapes using a high and a low level of extraction and three levels of total sulphur dioxide (0, 75 and 150 mg SO2 kg−1). From this single experiment, the effects of total SO2 and extraction on anthocyanin composition and colour were observed by HPLC, spectrophotometry and tristimulus colorimetry. High extraction produced a wine with more total pigments and total phenols than low extraction and increased the amount of organic acids extracted during fermentation. More anthocyanins were extracted with increasing SO2 levels. On maturation, all wines lost colour and increased in brownness. Wines made without SO2 browned more than the wines made with SO2. The anthocyanins normally present in wines were all rapidly lost to trace levels at 24 months. Vitisin A, a more stable and highly coloured anthocyanin than malvidin 3-glucoside, showed a slower decrease in concentration than malvidin 3-glucoside and contributed significantly to the wine colour during aging. At the first analysis, the wines made without SO2 had a higher percentage colour due to polymers than the wines made with SO2. Polymerisation progressed during maturation, although the initial differences were maintained. Sensory analysis after 6 and 18 months storage by expert tasters revealed differences mainly related to the colour attributes, indicating that when wines are made using modern hygienic techniques, total SO2 has a negligible effect on aroma and flavour attributes.

Anthocyanin and colour evolution during maturation of four port wines: effect of pyruvic acid addition

The formation of vitisin A-type compounds has been studied in four maturing fortified red port wines stored for 29 weeks at 15 °C. The anthocyanin concentrations were determined by high-pressure liquid chromatography (HPLC), and colour changes were monitored by spectrometric measurements. The losses of anthocyanins followed first-order reactions, and the concurrent formation of polymeric pigments was demonstrated. Vitisin A-type compounds were found to be in low concentration in these four naturally maturing fortified wines. The addition of pyruvic acid to the wines led to the formation of large concentrations of vitisin A derivatives. Up to 23 mg litre−1 vitisin A derivatives (vitisin A and its acylated forms acetylvitisin A and p-coumarylvitisin A) could be determined. Owing to their greater colour expression and greater stability than malvidin 3-glucoside, these new anthocyanins were shown to play an important role in the colour quality of the wines. An analytical survey of 32 port wines matured for between 2 and 6 years showed that vitisin A-type compounds were the main, and sometimes the only, anthocyanins present. © 2000 Society of Chemical Industry