Wine Chemistry and Biochemistry

(Steven Felgate) #1

426 M.A. Pozo-Bay ́ ́ on and G. Reineccius


5-hydroxymethylfurfuraldehyde [HMF] and 5-methylfurfuraldehyde [5-OHFA]) and


phenolic aldehydes (vanillin and syringaldehyde) in wine-like model solutions. The


reactivity of both aldehyde families was very different: furanic aldehydes were


more reactive than phenolic aldehydes (HMF was the most reactive, followed by


FA, 5-OHFA, syringaldehyde and finallyvanillin). Dependingupon the aldehyde,


the product formed was very different. Thus, the formation of these condensation


products could play an important role in wine flavour development when aged in


oak barrels.


It has been suggested that anthocyanins can form hydrogen bonds with some


aroma compounds when they are present at high concentrations (Voilley et al. 1991).


Dufour and Sauvaitre (2000) reported that at pH 3.5, malvin, the hemiacetal form


of the anthocyanin 3,5 diglucoside, was primarily responsible for aroma interac-


tions rather than the main anthocyanin, malvidin-3-glucoside. They also reported


that benzaldehyde, furfural, and 2-isobutyl-3-methoxypyrazine did not contribute as


copigments whereas all phenol-based flavour compounds (e.g. vanillin, syringalde-


hyde) led to copigmentation. Although they did not observe any visible effect on


color by increasing the concentration of anthocyanins, the interactions of volatile


compounds with the anthocyanins may affect the sensory characteristics of wines.


Also during the aging of wine in oak casks, Escalona et al. (2002) have shown that


some phenolic compounds extracted from the wood (ellagic tannins) could partici-


pate in polymerization reactions with aroma compounds.


Some NMR studies (Jung et al. 2000) have confirmed that interactions between


some polyphenols (gallic acid and naringine) and some aroma compounds (e.g.
ethyl hexanoate and 2-methylpyrazine) are due toπ-πstacking of the gallic acid


ring with the aromatic ring of a flavour compound. Hydrogen bonding between


functional groups of a flavour compound and a polyphenol provide stability to the


complex and help to orient the molecules in a specific conformation. Nevertheless,


other studies performed with alkyl-methoxypyrazines in wine model systems sup-


plemented with some of these polyphenols (e.g. gallic acid) did not shown any mea-


surable effect (Hartmann et al. 2002), confirming the different effects of polyphenols


depending on the type of aroma compound being considered.


Most of the studies on polyphenol/aroma compound interactions have been based


on analytical determinations but there are few sensory studies documenting the


effect of polyphenols on wine flavour. However, Aronson and Ebeler (2004) have


shown that gallic acid (in 1% ethanol solution) significantly decreased the volatil-


ity of 2-methylpyrazine, while naringin at the same level had little effect. They


also found that ethyl benzoate had little interaction with either polyphenol. One


of the most valuable findings of this work was the agreement between the analytical


and sensory data showing the effect of gallic acid and naringine interactions with


2-methylpyrazine.


8F.2.2.3 Polysaccharides and Proteins


Wine polysaccharides, ranging from 500 to 1500 mg/L (Will and Dietrich 1990),


mainly come from grape primary cell walls, and from autolysis of micro-organisms

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