Grapes - Crop Post-Harvest: Science and Technology - page 191

2006). Malic acid is a very active intermediate in grape
metabolism. At veraison acid levels start to go down. The
decline in malic acid content is very rapid and is thought to
be due to respiration via oxidative phosphorylation. The
reduction in acidity is quicker under warm growing condi-
tions (Kanellis & Roubellakis-Angelakis 1993). After verai-
son, two vacuolar proton pumps have been detected that
create a positive membrane potential across the tonoplast
resulting in the accumulation of organic acids inside the vac-
uole. The activity of these pumps increased in parallel during
the period of sugar storage, while malic acid content
decreased (Terrier & Romieu 2001). IAA, GA and ABA pro-
moted the transformation of 14 C-sucrose into organic acid at
stage I, significantly inhibiting transformation at stage II
(Xia et al . 2000).

found that most of them were induced by light in grape
seedlings. The induction of the main genes involved in the
anthocyanin pathway is probably resulting from complex
interactions between various signals such as light, sugar,
abscisic acid and ethylene among others (Mol et al .1996).
Boss et al . (1996a) observed the expression of these genes
in white and red grapes, the non-expression of some of
these genes being correlated to the absence of anthocya-
nins. The transcription of most of these genes was clearly
induced at veraison (Boss et al . 1996b). The UDP-flavonoid
glycosyl transferase plays an important role in the redness
of the berry tissues (Boss et al . 1996a; Kobayashi et al .
2004 and refs herein), catalyzing a step that is known to
stabilise the anthocyanins (Piffaut et al . 1994). A recent
study points out the role of a transcription factor involved
in phenylpropanoid pathways (Deluc et al . 2006). Plant
hormones like auxin and abscisic acid may play a role on
the expression of these genes (Davies et al . 1997). From a
physiological point of view, some competition between the
anthocyanin and stilbene synthesis has been highlighted
(Jeandet et al . 1995).
Some recent advances in anthocyanin analysis by elec-
trospray ionisation mass spectrometry have been reported
(Sarni-Manchado et al . 1997). In the last decade, some
studies have focussed on the antioxidant properties of the
grape anthocyanins and associated variations between red
and white, young and old wines (Tubaro et al . 1999).

Phenolic components
Tannins (proanthocyanidins) are the most abundant class
of phenolics in grape berries and are the predominant
determinants of astringency in red wines (Souquet et al .
1996; Cheynier et al . 1997). Other major phenolic
compounds in grapes include anthocyanins, benzoic
acids, cinnamic acids and flavonols (Flanzy 1998). Berry
skins contain more hydroxycinnamic tartrates than the
flesh, while the latter has more flavan-3-ols and procya-
nidins. The composition of grape skin proanthocyanidins
at different stages of berry development has also been
described by Kennedy et al . (2001). The seeds have high
amounts of phenolics which form a significant propor-
tion of wine tannins and contribute significantly to oxi-
dative browning of grape juice. There has been
considerable interest in the chemical properties of grape-
vine polyphenols, including nonflavonoids (stilbenes,
phenolic acid derivatives) and flavonoids (flavanols,
flavonols and anthocyanins), and their biological and
pharmacological activities (Vitrac et al . 2004). A recent
work has been published about the expression of differ-
ent flavonol synthases in grape vines and berries (Fujita
et al . 2006).
Anthocyanins give rise to the red and purple colouration
of certain grape cultivars and are thus important quality
factors in table grapes and wine. The malvidin derivatives
are generally the most abundant anthocyanins in grapes.
Interesting reviews have been published recently about
anthocyanin content in wine grapes (Mazza 1995) and
table grapes (Carreño et al . 1997). During the last 20 years,
there have been several studies on the gene expression of
anthocyanins summarised by Holton and Cornish (1995).
In grapes, the cloning of various genes of the anthocyanin
pathway was performed by Sparvoli et al . (1994). They

Aromatic compounds
The aroma of grapes is attributed to over a hundred different
compounds, mostly located in the skin. Some cultivars from
the species V. labrusca and V. rotundifolia have very distinct
aromas, as do the Muscat types of V. vinifera although other
cultivars of this species are not highly aromatic. Some
aroma compounds are isoprenoid secondary metabolites
such as monoterpenes and damascenone (Jackson 2000).
It has been suggested that their synthesis is linked to the
formation of lipid-like globules in plastids found in the
pericarp (Hardie et al . 1996). Some other aroma precursors
are present in a glycosylated form (Williams et al . 1995).

Hormonal changes
The hormonal changes from anthesis to maturation of the
berry are well summarised in the review by Kanellis and
Roubellakis-Angelakis (1993). Very little is known about
the post-harvest role of phyto-hormones in grapes.

Gibberellic acids
The size of mature berries correlates well with the number
of seeds and parthenocarpic or stenospermocarpic cultivars