Phenolics in wine

P. Vinas, C. Lopez-Erroz, J.J. Marin-Hemandez and M. Henandez-Cordoba, Determination of phenols in wines by liquid chromatography with photodiode array and fluorescence detection. 

Methods of analysis are needed to determine total phenolic content and the relative content of phenolic fractions by means of their different characteristics. Many analytical methods used for phenols have been empirical and not easily reproduced or rationalized (I). Procedures that are based on sound chemical principles and that are sufficiently verified deserve wider application. We are concerned here with recent work on such analyses for phenols in wines. Application cf these results may help solve a major problem in phenol research—the many different, too empirical, unrelatable values (ml KMn04, vanillin-to-leucoantho-cyanin ratio, etc.) obtained in different ways by different researchers. Uniform use of verified methods and uniform standards and methods of expressing results will aid in developing an understanding in this field. 

The colorimetric method based on the reagents of Folin and Denis or of Folin and Ciocalteu has been generally preferred over other methods to determine total phenols in complex natural materials such as wines and fruits (1, 2, 3, 4, 5). This method is relatively simple, convenient, reliable, generally applicable, and it is accepted as an official analysis in several countries for total phenols in wines and a number of other products. Although it is a preferred method, it can be even better than is commonly recognized. 

Singleton, V.L. 1988. Wine phenols. In Wine Analysis (H.F. Linskens, and J.F. Jackson, eds.) pp. 173-218. Springer-Verlag, Berlin. 

Davalos, A. and Lasuncion, M. A. (2009). Health-promoting effects of wine phenolics. In Wine Chemistry and Biochemistry", (M. V. Moreno-Arribas and M. C. Polo, Eds), pp. 571-591. Springer, New York. 

Roggero, J.P. Archier, P. Coen, S. 1997. Chromatography of phenolics in wine. In Wine Nutritional and Therapeutie Benefits. ACS Symposium Series Vol. 661, American Chemical Society, Washington D.C., pp. 6-11. 

Grapes contain several hydroxycinnamic acids, p-coumaric, caffeic, ferulic and sinapic acids, which exist as free acids and esterified with tartaric acid. Saccha-romyces species can take up free acids to produce the corresponding vinyl phenol catalysed by hydroxycinnamate decarboxylase (phenylacrylic acid decarboxylase Padlp) (Fig 8D.11) (Chatonnet et al. 1992b Chatonnet et al. 1993 Edlin et al. 1995). Vinyl phenols are unstable and highly reactive. Dekkera bruxellensis is one of few wine microorganisms that can further reduce vinyl phenols to highly stable ethyl phenols in wine. Vinyl phenols can also react with anthocyanins to form vinyl derivatives, a reaction that is favoured by fermentation yeast having hydroxycinnamate decarboxylase activity (Morata et al. 2006). 

More potent yeasts responsible for spoilages of wines with volatile phenols are of Brettanomyces/Dekkerra type that can produce the vinyl phenols and ethyl phenols of hydroxyl cinnamic acids. Ribdreau-Gayon et al. (2000) give an overview on this topic. Another source of volatile phenols is the oak wood of barrel and oak chips. These phenols are characterized by smoked and toasted aromas. Important volatile phenols in wine are depicted in Fig. 9C.4. 

Table 11.5 Metabolic activity of microorganisms related with production of volatile phenols in wine industry... 

Larcher, R., Nicolini, G., Puecher, C., Bertoldi, D., Moser, S., Favaro, G. (2007). Determination of volatile phenols in wine using high-performance liquid chromatography with a coulometric array detector. Anal. Chim. Acta, 582, 55-60. 

Mejias, R.C., Matin, R.N., Moreno, M.V.G., Barroso, C.G. (2003). Optimisation of headspace solid-phase microextraction for the analysis of volatile phenols in wine. J. Chromatogr. A, 995, 11-20. 

Phenols and polyphenols in wine are transferred from the grape in the winemaking and are released from the wood barrels used for the wine ageing. The principal low MW phenols in wine are reported in Figure 3.1. 

Figure 3.1 Structures of principal low molecular weight phenols in wine (1) pyrocatechol (2) resorcinol (3) hydroquinone (4) phloroglucinol (5) vanillin (6) p-hydroxybenzaldehyde (7) syringic aldehyde (8) coniferyl aldehyde (9) sinap-inaidehyde (10) gentisic acid (11) gallic acid (12) vanillic acid (13) salicylic acid (14) syringic acid (15) caffeic acid (16) ferulic acid (17) p-coumaric acid (18) hydrox-ycinnamoyltartaric acids (R = H, OH, OCH3)...

Table 3.2 Negative-ion ESI mass spectra of low MW phenols in wine (Perez-Margarino et al., 1999).

Dubois, P. (1983) Volatile Phenols in Wines, in Flavour of distilled beverages, origin and development, J.R. Piggot (Ed.) Chichester Ellis Horwood. 

The experimental conditions for MHS-SPME-GC/MS/MS of volatile phenols in wines are reported in Table 5.14. The MS/MS parameters and method performances are reported in Table 5.15. 

TABLE 5.15. Multiple Headspace SPME-GC/MS/MS Method (n = 3) for Analysis of Volatile Phenols in Wines MS/MS Parameters and Performances"... 

Ethoxyhexadiene 268 Ethyl Carbamate 265 Ethyl Phenols in wines 143... 

Vinyl Phenols in wines 143 Volatile compounds in wood 226... 

Dubois P. (1983) Volatile phenols in wines. Flavour of Distilled Beverages. Origin and Development. Piggott J.R. Ed., Ellis Horwood, Chichester, p. 110. 

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