Wine Chemistry and Biochemistry

8A Wine Aroma Precursors 257

degradations by chemical, photochemical or coupled to oxidases (lipoxygenase,

polyphenoloxidase, xanthineoxidase) reactions were knownwell before carotenoid

cleavage dioxygenases in plants, as reported in reviews (Winterhalter and Rous-

eff 2000; Wirth et al. 2001), but they have not been unambiguously demonstrated

in winemaking. If they occur, these reactions would be alternative pathways leading

to norisoprenoidic compounds directly from xanthophylls, as hypothesized recently

(Silva Ferreira and Guedes de Pinho 2004). However, they would be minor pathways

indeed, as evidenced by the trace amounts of -ionone found in most wines (about 1

g/L), relative to that of -carotene found in grapes (about 1 mg/L) (Bureau 1998;

Kotseridis et al. 1998). Obviously, these pathways would be more important in forti-

fied wines containing carotenoids, such as Port wines (Guedes de Pinho et al. 2001),

than in other wines, for which the effective time for carotenoid degradation would

be limited to the time of contact between the solid and liquid portions of the must.

8A.5 Glycoconjugates

The occurrence inVitis viniferagrape of glycoconjugates of volatile compounds

(glycosidically bound volatiles) were suggested first for monoterpenols by Cor-

donnier and Bayonove (1974). Afterwards, extensive research showed that this

group of precursors consisted of a lot of derivatives, including four sub-groups

according to the sugar moiety, - D-glucopyranosides, 6-O- - L-arabinofuranosyl-

• D-glucopyranosides, 6-O- - L-rhamnopyranosyl- - D-glucopyranosides and 6-O-


• D-apiofuranosyl- - D-glucopyranosides, each with aglycon moiety belonging to

different classes of volatiles, mostly monoterpenoids, C13-norisoprenoids, volatile
phenols, C6 compounds, aliphatic, benzyl and 2-phenethyl alcohols and some other

compounds (Fig. 8A.5) (Baumes et al. 1994; Cox et al. 2005; G ̈unata 1984, 1985a,b;

Sefton et al. 1989, 1993; Stahl-Biskup et al. 1993; Strauss et al. 1987a–c, 1988;

Voirin 1990; Voirin et al. 1990, 1992; Williams et al.1982a,b, 1983, 1984;

Winterhalter and Skouroumounis 1997; Wirth et al. 2001). In grape berry, most

volatile phenols, monoterpenoids and C13 norisoprenoids occur as glycoconjugates,

Fig. 8A.5Glycoconjugate
general structure, and the
different groups of sugar and
aglycon moieties occurring in
grape

H

Apiose

Rhamnose

Arabinose

Alcohols

C 6 alcohols

Monoterpenols

Volatile phenols

C 13 -Norisoprenoids

Glucose

moiety

O

HO

OH

OH

O

O

Sugar AglyconAglycon