Carlos Díaz-Romero

Effect of Caffeic Acid on the Color of Red Wine

The copigmentation effect of prefermentation additions of different doses of caffeic acid was investigated during the 1997 harvest. Microfermentation with the major red grape cultivars Listán negro and Negramoll, grown in the Canary Islands, was carried out with the same protocol. Visible and UV spectra were registered periodically. HPLC chromatograms were carried out. The color enhancement of cv. Negramoll wine varied between 13 and 75% (AU at 520 nm), and that of cv. Listán negro wine between 25 and 45% at the end of fermentation. During aging these values were enhanced to reach even >100% in some cases. An initial complex of the 1:1 type, where one molecule of caffeic acid associates with one molecule of anthocyanin, has been identified using the mathematical procedure of Brouillard et al. (J. Am. Chem. Soc. 1989, 111, 2604-2610). Caffeic acid seems to contribute to color stability and protection against oxidation. The importance of nonpigment composition in pigment extraction and color retention during and after fermentation is demonstrated.

Comparative study of methods for determination of titrable acidity in wine

A comparative study of three methods for titrable acidity determination in must and wines was carried out. Titrable acidity (TA) was analysed in 115 wines from the Canary Islands by conductance titration, AOAC and OIV procedures. Conductivity, pH, malic acid, tartaric acid and potassium content were also determined. The results of TA obtained depended on the method used, however, a highly significant correlation between these methods was found. Conductance titration showed that the true end point is in pH values higher than those of the AOAC and OIV procedures. In order to compare the results of TA obtained in different countries by AOAC and OIV procedures, the use of some expressions, one for red wine and one for white wine, is proposed. An important differentiation between red and white wine mean discrimination analysis using pH values, malic acid and potassium content could be observed.

Copigmentation, colour and antioxidant activity of single-cultivar red wines

Abstract A hundred and thirty-six single-cultivar red wines of different vintages were collected from several wineries in the Canary Islands in order to study the magnitude of the copigmentation phenomenon and the antioxidant activity. The contribution of free anthocyanins, copigmented anthocyanins and polymeric pigments to the colour of wine, as well as the total phenols, the antioxidant activity (2,2-diphenyl-1-picrylhydrazyl, DPPH method) and the chromatic characteristics of the wines were determined. The influence of ageing time and the climatic conditions on these parameters was also studied. The wines made with Merlot, Ruby Cabernet and Syrah cultivars showed the highest parameters of colour, and the largest contribution to the copigmented anthocyanins was from the Ruby Cabernet, Listán negro and Syrah cultivars. The copigmented anthocyanins and the free anthocyanins decrease with the age of the wine, and the antioxidant activity of the samples appears to be related to the total phenol content. An influence of the climatic conditions on colour parameters has been found. The correlation study between parameters suggests that the parameters b* and L* could be used as suitable indicators of evolution or oxidation stage of red wines.

A comprehensive study of red wine properties according to variety.

More than 80 properties have been studied in 250 commercial red wines to obtain a reliable description of the characteristics of each variety. Such a large set of data allows the testing of previous assumptions and a thorough investigation about whether varietal discrimination is possible despite the strong influences of ageing and environment. Even though several studies have been performed regarding how variety influences wine phenolics or colour, only a few count on a large data set. Most studies are performed by applying only one technology or on a limited number of wines. In this work, a heterogeneous wine population is thoroughly analysed by using diverse analytical techniques. Therefore, analysis of variance can be applied and patterns are observable in different parameters like flavonols or anthocyanins in spite of the high heterogeneity of the samples. The study confirms that discriminant analysis can be successful in distinguishing wines according to variety in spite of the influences of winemaking techniques and vintage.

Influence of copigmentation and phenolic composition on wine color.

Chromatic characteristics and their relationships with copigmentation and phenolic composition were studied in 160 bottled red wines. Free anthocyanins, copigmented anthocyanins and polymeric pigments contributing to color were calculated according to Boulton protocol and related to main changes produced in wine visible spectra after destroying any copigmented anthocyanins effect. Color differences between copigmented and non copigmented wines were quantified and related with ageing, cultivar and phenolic profile. Phenomenon of co-pigmentation visually increases the colour at 420, 520 and 620 nm for most of wines. Copigmented wines showed a mean value of 8.26 CIELab units higher than non copigmented (ΔEab(c-nc)), being this shift deeper for young wines than for aged wines. Copigmentation mostly changed hue and decreased L, a* and b* values therefore resulted into purplish and darker wine. Visual variations in color caused by copigmentation was related to particularly anthocyanins and copigments (mostly flavonols and hydroxycinnamic acids).