Agriculture Reference
In-Depth Information
attributes are highlighted on different parts of these maps
and in most cases for apples they are closely associated
with the key taste and texture attributes of the fruit.
HO
COO
COOH
HO
NUTRITIONAL VALUE AND HUMAN HEALTH
The nutritional value of fruit and vegetables are becoming
a more important determinant of consumer choice. Apples
are a good nutritional source of dietary fibre and Vitamin C
and are very low in saturated fat, cholesterol and sodium
(Wills
et al
. 2007). In addition to these standard nutritional
contents, apples are becoming desirable because they
are a rich source of phytochemicals, namely, phenolics
(Boyer & Liu 2004). Phenolics are well-known antioxi-
dants that have been shown to benefit human health. It has
been estimated that apples contribute 22% of the American
consumption of fruit phenolics (Vinson
et al
. 2001).
Phenolics are naturally occurring compounds that are
derived from phenylalanine via the shikimate and phenyl-
propanoid pathways and are widely found in apples
(Macheix
et al
. 1990). The major classes of phenolics in
apple peel include phenolic acids (hydroxybenzoic acids),
hydroxycinnamic acids (chlorogenic acid) and the
flavonoids, for example flavans (catechin), procyanidins
(condensed tannins), flavonols (quercetin glycosides),
chalcones (phloretin glycoside) and anthocyanins (cyanidin
glycosides) (Figure 5.5).
The growing human interest in apple phenolics is their
role in the human diet. Epidemiological studies have
linked the consumption of apples with reduced risk of
some cancers, cardiovascular disease, asthma and diabetes
(Boyer & Liu 2004). Apple phenolics possess significant
antioxidant potential and have been shown to inhibit
cancer cell proliferation, decrease lipid oxidation and
lower cholesterol in laboratory tests (Boyer & Liu 2004).
The role of phenolics in the apple fruit is unclear, but
they may play an important part in the physiology and
metabolism. For example, phenolics act as substrates
for browning enzymes, they are important antioxidants
(Wills
et al
. 2007) and they have also been implicated in
pathogen resistance and some physiological disorders
(Macheix
et al
. 1990).
The phenolic content of apples varies by variety,
environmental growing (nutrient) conditions and location
within the tree (Awad
et al
. 2001, 2002). For example, lower
levels of some phenolics such as catechin and chlorogenic
acid are not affected by canopy position, but others such as
anthocyanins are affected by tree position (Awad
et al
.
2001). Not surprisingly, significant differences in phenolic
concentrations in fruit from different regions for some
varieties have been reported (McGhie
et al
. 2005).
HO
OH
OH
Hydrocinnamic acid derivative
5'-caffeoylquinic acid
Chlorogenic acid
OH
OH
HO
O
O
glucose
rhamnose
O
HO
Flavonol
quercetin rutinoside
Rutin
Figure 5.5
Important apple phenolics: chlorogenic
acid and rutin.
There are only relatively small changes in fruit phenolics
during maturation and ripening, where their levels are
relatively stable during air and CA storage for over nine
months (Golding
et al
. 2001), indicating that phenolic
metabolism and turnover are low during storage.
PRE-HARVEST FACTORS AFFECTING
STORAGE
It is important to remember that fruit are alive while
they are on the tree and remain alive during post-harvest
storage. While the fruit is attached to the tree, it is growing
and accumulating carbohydrates and other nutrients. These
stored reserves sustain the fruit during post-harvest storage
and marketing. This means that any factor which limits the
growth and accumulation of stored reserves of the fruit
while it is on the tree can also affect the fruit's post-harvest
storage life (Sharples 1975; Little & Holmes 2000; Stanley
et al
. 2000).
Often the effects of climate on storage life are small and
only affect such things as fruit size, shape, red colour and
blemish more than their storage potential (Little & Holmes
2000). However, in some instances the effect of climate, or
the interaction between climate and orchard management,
