Wine Chemistry and Biochemistry

(Steven Felgate) #1

548 C. Santos-Buelga and V. de Freitas


alcoholic fermentation, in which the formation of ethyl-linked polymers can be


expected to contribute to the anthocyanin losses by precipitation. In further stages of


wine life some amounts of acetaldehyde canalso be produced during malolactic fer-


mentation as well as from ethanol by coupled oxidation of polyphenols (Wildenradt


and Singleton 1974). In these stages lessacetaldehyde is available and the condi-


tions are less favorable for the formation of condensed pigments, so that no great


amounts of them are expected to be formed. Nevertheless, although these pigments


are not expected to contribute directly to the color of red wines, they could play an


important indirect role on the color changes due to their contribution to anthocyanin


losses by precipitation in early stages of winemaking and further involvement in the


formation of flavan-pyranoanthocyanins.


In addition to acetaldehyde, other aldehydes can also exist in wines (e.g., pro-


pionaldehyde, isovaleraldehyde, isobutyraldehyde, benzaldehyde or vanillinalde-


hyde), released from the wood of the barrels used in the aging process or as a result


of the addition of wine spirit in the case of fortified wines like Port wine. These


compounds can also be involved in the formation of alkyl/aryl adducts between


anthocyanins and flavanols similar to those induced by acetaldehyde


(Pissarra et al. 2003, 2004, 2005; Sousa et al. 2007). The UV-visible spectra of


all these pigments display a bathochromic shift in theirmaxin relation to that of the


parent anthocyanins, resulting in a “blueing” effect of different magnitude depend-


ing on the aldehyde. Thus, the bathochromic shift seems to be higher for branched


aldehydes, like benzaldehyde or isobutyraldehyde, than for non-branched ones (e.g.,


acetaldehyde, isovaleraldehyde or propionaldehyde). The steric hindrance promoted
by the more branched substituents probably favors a more -electron conjugated


conformation leading to a greater displacement of themaxin the visible region


(Pissarra et al. 2003). This pigment family could play a significant role in the color


of Port wines, especially during the initial stages of aging. The content and profile


of aldehydes in the wine spirit added would determine the type of aryl/alkyl adducts


formed, with different chromatic characteristics, thus having an influence on color


definition (Pissarra et al. 2004). The possibility of some aldehydes extracted during


oak aging being involved in the formation of pigments cannot be discarded either.


Quite recently a pigment from the condensation between malvidin 3-glucoside and


catechin mediated by vanillin aldehyde has been characterised (Sousa et al. 2007).


This aldehyde is reported to occur in oak aged wines as released from wood


(Escalona et al. 2002).


9D.2.3.4 Anthocyanin-flavanol Condensed Pigments


The formation in red wines of anthocyanin-flavanol adducts had been early hypothe-


sised by Jurd (1967, 1969). Two types of adducts seem possible, (1) F-A derivatives


resulting from the nucleophilic addition of the hemiketal form of an anthocyanin


through their C-8 or C-6 positions at C-4 of a carbocation resulting from the cleav-


age of a procyanidin, and (2) A-F derivatives from the electrophilic substitution


of the anthocyanin flavylium form (C-4) by a flavanol (C-8 or C-6). The former

Free download pdf