Aldehydes in grapes

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. 

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

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). 

In a companion study, M. Palma et al. studied the extraction of grape seeds with pure SF CO2 and analyzed the derivatized extracts by GC-MS. These extracts were found to contain volatiles such as aliphatic aldehydes in addition to fatty acids and sterols. Even though we used similar conditions for our SF extraction and GC-MS analysis, we were unable to detect any similar volatile compounds. To further investigate the presence of volatiles in the cranberry seed extract, we adapted a solid phase microextraction (SPME) method from the work of Jelen et al. who had earlier developed it for the characterization of volatile compounds in different vegetable oils. SPME followed by gas chromatog[raphy was performed on the headspace of the cranberry seed extract to test for the presence of volatile compounds. The GC trace failed to show the elution of any components for either the SF or Soxhlet extract. 

The skin is considered to be the principal source of aromatic substances, but the pulp does contain significant concentrations of these compounds. In certain muscat varieties, the must can contain up to two-thirds of the terpenol heterosides. The pulp is characterized in particular by the accumulation of a diverse variety of alcohols, aldehydes and esters which participate in grape aromas. 

Several hundred different chentical substances participate in grape aroma. In this complex mixture, hydrocarbides, alcohols, esters, aldehydes and other carbon-based compounds can be distinguished (Schreier et al 1976). 

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. 

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). 

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