Wine Chemistry and Biochemistry

8A Wine Aroma Precursors 253

(Z) -Unsaturated fatty acids

Phosphoric acid

Glycerol

Mono/oligosaccharide

(galactose)

Sterol

CH 3 (CH 2 )

CH CH

(CH 2 )(CH 2 ) 6 CO 2 R

n

k

k = 1 + 3x(3-n)

nn^ == 2 2 Linoleic Linoleic aacicidd 1188 :2 (9,12) :2 (9,12)

nn == 3 3 Linolenic Linolenic aacicidd 1188 :3 (9,12,15) :3 (9,12,15)

C6C6--comcomppoouunnddss

PrecPrecuursorsrsors

Fig. 8A.2Major grape unsaturated acyl lipids, precursors of C6 compounds

these C6 compounds, odorants with green and grassy olfactive notes, depends not

only on the contents of unsaturated lipids, but also on activities of the enzymes

involved, and thus defined, some differences were observed between grape culti-

vars (Valentin 1993). However, these enzymatic activities are much more dependent

on berry maturation than on grape cultivar. In addition, the C6-aldehydes are very

powerful odorants in must, but they are almost totally reduced during the alcoholic

fermentation by yeast to hexanol, whichhardly exceeds its olfactive perception

threshold in wine (Eti ́evant 1991). In contrast, the minor C6-compounds found in

wine, hex-2- and 3-en-1- ols, are more powerful odorants than hexanol, but they

usually occur in much lower levels and do not contribute to wine aroma, except for

generating unpleasant herbaceous off-odors (Joslin and Ough 1978).

8A.3 Phenolic Acids

Another class of aroma precursors, phenolic acids, presents a similar case. These

hydroxycinnamic acids occur mostly in grape as esters with tartaric acid (a hydroxyl

group of tartaric acid is esterified by the phenolic acid), the E configuration of the

cinnamic double bond being preferred (Fig. 8A.3) (Singleton et al. 1978). The most

abundant tartaric esters of grape hydroxycinnamic acids are caftaric acid (< 800

mg/kg), ester of caffeic acid, coutaric acid (<300 mg/kg), ester of coumaric acid,

and fertaric acid (<60 mg/kg), ester of ferulic acid. These compounds are primarily

located in the solid parts of the berry, and their contents decrease with maturation

(Rib ́ereau-Gayon 1965; Romeyer et al. 1983). In contrast to lipids, their contents

differentiate grape cultivars, and the percentages of their distribution have been

proposed as taxonomic criterion (Boursiquot et al. 1986). However, their minor