Grapes aldehydes

Table IV. Formation of ( -aldehydes and Cg-alcohols (/tg/100 grams) in Grapes and in Vine Leaves...

The Scuppemong grape has a distinctive flavor characteristic. Kep-ner and Webb (47) analyzed the volatile essence of this grape and identified six alcohols, including 0-phenylethyl alcohol, five aldehydes, and five esters. No nitrogen or sulfur containing compounds were found which indicated the absence of methyl anthranilate. 

Most of the studies on Botrytis-specific aroma compounds have investigated the aroma composition of wines (Table 6.7). Only a few have focused on what occurs in the grape. On synthetic media, the main odorous compounds produced by B. cinerea are aromatic aldehydes (benzaldehyde, phenylacetaldehyde), and furfural (Kikuchi et al., 1983). Sarrazin et al. (2007a) confirmed the higher concentration of phenylacetaldehyde in noble-rotted grapes. 

FIGURE 7.6 Short-chain aldehydes and alcohols produced from the degradation of fatty acids in grapes via the lipoxygenase (LOX)/hydroperoxide lyase (HPL) pathway during the prefermentative stages of vinification (adapted from Camara, 2004). 

High levels of S02 (200 mg/L) may affect initiation and length of fermentation and result in higher aldehyde content after fermentation (25). Desirable juice levels of S02 are 50-100 mg/L S02, depending on grape condition. 

Yeast-derived saturated short-medium chain and branched-chain aldehydes are formed from sugar metabolism, fatty acid metabolism and branched-chain amino acid metabolism (Fig 8D.7). In addition, hexanal, as well as hexenal isomers, are formed during the pre-fermentative stages of winemaking by the sequential action of grape lipoxygenase and hydroperoxide cleavage enzyme on linoleic and linolenic acid, respectively (Crouzet 1986). 

Chemical Reactions of Aldehydes in Grapes and Wines. The short chain, volatile aldehydes are quite reactive making accurate analysis and quantitation difficult. In addition, many of these reactions are equilibrium reactions with the concentration of unreacted and reacted aldehydes being lughly dependent on the analysis conditions. 

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