Grapes - Crop Post-Harvest: Science and Technology - page 190

the later part of stage I and early part of stage III. Fully ripe
berries show practically no photosynthetic activity (Koch &
Alleweldt 1978; Niimi & Torikata 1979). Using the cultivar
Cabernet Sauvignon, Ollat et al . (2000) found that during
the whole growth period, the grape berry imported
12 mmoles of carbon. Respiration accounted for 18% of
the imported carbon and fruit photosynthesis supplied 10%
of the carbon required for fruit development. When fruit of
the Pusa seedless variety were harvested at maturity and
stored at 1°C, respiration rate declined for 30 days and rose
thereafter (Rao et al . 1975).

transport are still poorly understood. It is possible that an
increase in berry alcohol dehydrogenase activity is linked
to fruit ripening (Tesniere & Verries 2000) and that Adh 2
expression depends upon ethylene signalling (Tesniere et
al . 2004). There are no clear physiological means to
explain these inductions yet. There is also evidence that
sucrose transporters may play a role in sugar accumulation
(Davies et al . 1999). A hexose transporter gene (Vvht1)
has been cloned and shows a first peak of expression at
anthesis, and a second peak about 5 weeks after veraison.
The Vvht1 promoter sequence contains several potential
regulating cis elements, including ethylene-, abscisic acid-,
and sugar-responsive boxes (Fillion et al . 1999).
The effects of hormones on sucrose accumulation and
metabolism at different developmental stages (I, II,
veraison and III) were investigated by Xia et al . (2000).
Gibberellic acid (GA), indoleacetic acid (IAA) and abscisic
acid (ABA) all significantly facilitated 14 C-sucrose import
into the berries at all stages studied but caused differing
effects on the subsequent transformation of the sucrose.
For example, the transformation of 14 C-sucrose to reducing
sugars was enhanced by IAA whereas GA increased the
accumulation of fructose. Recently, ethylene has been
proved to regulate the sucrose transport into berries
(Chervin et al . 2006).

Solute accumulation
Sugars and minerals
The accumulation of sugars is the most important quality
change in the ripening fruit. It is these sugars which are
converted into alcohol during wine making and which give
the sweetness desired in both fresh and dried fruit and fruit
juice. It is not therefore surprising that there is considera-
ble interest in understanding the processes that control the
production and accumulation of sugars.
From anthesis to veraison, imported carbon (in the form
of sucrose) is almost equally partitioned between pericarp,
seed growth and respiration. At veraison, carbon imports
increase. Then the carbon is mainly allocated to the
pericarp and stored as the hexoses, glucose and fructose
(Ollat et al . 2000). These two sugars are the main carbohy-
drates of the mature berry pulp. They are present in
approximately equal amounts (total sugars = 12-27% fresh
weight) although the actual ratio varies between cultivars.
Cultivars with more fructose than glucose can be harvested
earlier due to the greater sweetness of this sugar compared
to glucose. As the fruit become over-mature, the fructose to
glucose ratio increases (Winkler et al . 1974).
Up to veraison, water is imported mainly through the
xylem. At the onset of ripening, the contribution of xylem
water is reduced by embolism blockage (Coombe 1992).
At this stage, carbon import increases fivefold due to a
stimulation of water flow through the phloem.
The back-flow, water movement from the berry to the
parent vine, may be an important component of berry
weight loss at maturity in some cultivars, such as Shiraz
(Tyerman et al . 2004). Mineral transport is related to the
pathway of water import. Calcium is translocated during
early berry growth while potassium is translocated during
ripening (Ollat & Gaudillere 1997). Although it has been
suggested that berry sink strength increases substantially at
the onset of ripening, the factors that control the massive
sugar import into the berries and the pathways of assimilate

Acids
The acidity level is a very important quality factor in both
table grapes and those used for wine production. Consumer
acceptance of table grapes and grape juice is strongly
influenced by the sweetness to acid balance (Winkler et al .
1974). Acidity also determines the suitability of the fruit
for wine making. Excessive tartness correlates with low
sugar levels which give poor-quality wine (Ruffner 1982).
However, in warm climates, grapes with a low pH and high
acidity levels are generally desired for table wines. The
brilliance and red intensity of coloured grapes is greater
at moderate to high acidity and low pH. With low acidity
and high pH, they tend to be bluish and dull (Winkler
et al . 1974).
A review article gives details about the biochemistry of the
acidity variations in grape berries (Terrier & Romieu 2001).
Tartaric and malic acids constitute over 90% of total acids (%
fresh weight); however, the ratio between the two acids var-
ies considerably depending on the grape cultivar. Both acids
accumulate before veraison although they show distinct pat-
terns of accumulation (Ruffner 1982). Tartaric acid is thought
to be stored both as insoluble calcium tartrates and as the free
acid in the vacuole. A recent study demonstrated that ascor-
bic acid is the precursor of the tartaric acid (DeBolt et al .