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Micro-oxygenation in Contemporary WinemakingThe acetaldehyde linking reaction can also occur with the tannin in dimeric or polymericforms resulting in large polymeric pigments.The indirect acetaldehyde-mediated condensation reactions occur much more rapidly thandirect condensation in the presence of acetaldehyde and so is more important in theproduction of polymeric pigments. The resulting compounds have higher colour intensityand stability (Es-Safi et al., 1999a; Es-Safi et al., 1999b).Acetaldehyde is not the only aldehyde that can produce such linkage reactions. Forexample, it has been shown that glyoxylic acid, produced from the oxidation of tartaric acid,and the furfurals can produce similar condensation reactions (Es-Safi et al., 2002;Monagas et al., 2005).6.2.5 Cyclo-addition Reactions Leading to the Formation of PyranoanthocyaninsThe last set of important reactions are those that produce pyranoanthocyanins. Thepyranoanthocyanins were discovered relatively recently and are formed by the addition ofan ethylene bond to C4 or C5 of the anthocyanin C-Ring (Fulcrand et al., 1996; Fulcrand etal., 2006). The added chain is then oxidised to produce a molecule with an additional pyranring (Figure 19).The resulting compounds are red-orange which suggests that they may be important inwine ageing, because none of the other products discussed so far are able to explain thetypical colour changes that occur with wine maturation (Francia-Aricha et al., 1997). Thepyranoanthocyanins are also very stable pigments resistant to changes in pH and SO 2bleaching.The pyranoanthocyanins can be formed though a number of different mechanisms. Mostimportant in terms of oxidation and micro-oxygenation are the reactions involving theaddition of acetaldehyde to the anthocyanin molecule (Atanasova et al., 2002) butpyranoanthocyanins are also formed by reactions involving pyruvate and vinyl phenols(Figure 19).52
Micro-oxygenation in Contemporary WinemakingOCH 3OCH 3OCH 3OHOHOHHOO +OCH 3HOOOCH 3HOO +OCH 3OGluCycloadditionOGluOxidationOGluHOOCOHδ +Cδ -CH 2-H 2OOCOOHOCOOHPyranoanthocyanin[Red-Orange]CH 3AcetaldehydeOCH 3OCH 3OCH 3OHOHOHHOOHδ +O +δ -CH 2OGluOCH 3CycloadditionHOHOOCH 3O GluO + HOxidationHOOO +OGluOCH 3Pyranoanthocyanin[Red-Orange]OHVinyl phenolOHOHFigure 19: Reactions Producing PyranoanthocyaninsDrawn from (Monagas et al., 2005)53
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ACKNOWLEDGEMENTSI must acknowledge
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LIST OF TABLESTable 1: Vinovation/O
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