Agriculture Reference
In-Depth Information
damage on apples during transport and handling was
conducted by Van Zeebroeck
et al
. (2007).
Apple packers have developed various methods of
'conditioning' the fruit to allow for a controlled amount
of moisture to be lost by the fruit by decreasing storage
humidity. This can reduce the turgor pressure within the peel
cells and this has been shown to reduce bruise susceptibility.
Some methods of conditioning include increasing the
number of defrost cycles, opening the doors and increasing
the temperature, or placing the bins in a warm room before
packing. It is easy to remove a small amount of moisture
from a cool room, but difficult to ensure that all fruit in a
bin are affected equally (Kupferman 2006). However,
Samim and Banks (1993) concluded that the potential for
decreasing bruise susceptibility in 'Granny Smith' apples by
manipulating fruit water status is quite limited. In addition,
removing water from the cool rooms (and hence from the
fruit) reduces the amount of saleable fruit and risks the
potential of excessive water loss resulting in shrivel.
All apples are susceptible to bruising. It is has been a
common preconception that 'Red Delicious' is more
resistant to bruising. Although the external symptoms on
the skin may not reveal classic bruise symptoms through
the highly blushed peel, the tissue immediately under the
skin often reveals classic brown bruise symptoms. Bruising
is particularly an issue for light-coloured varieties such as
'Pink Lady™' and 'Golden Delicious', where the bruising
symptoms are more obvious.
The most obvious method to reduce bruising is to try to
reduce or eliminate impacts that occur from harvest through
to packing. Careful and constant vigilance in minimising
fruit impact during harvest, transfer of fruit from the field
and in the packing house can significantly reduce bruising.
Often it is the imbalance between nutrients that causes the
problems. For example, calcium and boron are acquired by
the tree via the mass flow of water as it is drawn up through
transpiration. Therefore, when the demand for water is low,
such as cloudy weather, the transport of calcium is also
low (Little & Holmes 2000). In contrast, other essential
nutrients such as potassium and nitrogen are taken up
via active transport through the phloem and uptake is
influenced less by the weather (Little & Holmes 2000).
This very simple example shows how seasonal weather
conditions and their interaction with nutrient uptake
can influence the composition of the fruit and in turn its
post-harvest storability and quality.
Most calcium uptake into the fruit occurs in the first
weeks of the growing season and so different timings of the
water stress may cause different effects. For example,
water stress late in the season will reduce the final growth
and size of the fruit and may also reduce the 'dilution' of
the calcium concentration. Smaller fruit have a higher
concentration of calcium even though the total amount of
calcium is the same (Lakso 2003). Little and Holmes
(2000) detail the factors such as rootstock, crop load, prun-
ing and variety that influence calcium status of the fruit.
Another disorder, which is known as low temperature
breakdown (LTB), was the subject of one of the earliest
investigations into the effects of climatic conditions on the
storage life of apples, carried out by West in the 1930s
using samples of 'Bramley's Seedling' apples. West found
that the level of LTB was lower in fruit after warm dry
weather during the four weeks immediately preceding
harvest. This work also revealed that low rainfall and high
temperatures during that period were both associated with
reduced levels of LTB. There was, however, an interaction
between cool seasons, late picking and light crops with late
harvested fruit, from low cropping trees from cool seasons,
being more susceptible to the disorder (Sharples 1975).
Core flush is a disorder that occurs in apples that have
been harvested after a cool summer. For example, research
has shown that there is a negative correlation between core
flush in 'McIntosh' apples and solar radiation and
temperature during the last six weeks of the growing sea-
son (Sharples 1975). It has also been shown that fruit
grown under shade are more susceptible to core flush than
fruit grown in full sun (Sharples 1975).
Another factor to consider for seasonal climate is water
management and stress. There are often contradicting
reports about the impact of water stress on post-harvest
quality. This is because it is difficult to separate out the
effect of water stress and its interaction with other factors
(Lakso 2003). As detailed in the review by Lakso (2003),
Physiological disorders
Due to their long time in cold storage, apples are renowned
for developing storage disorders that are one of the major
storage impediments in storing apples. Disorders are
characterised by abnormal breakdown of tissue that is not
caused by mechanical damage nor invasion of pathogens
(Little
et al
. 1973; Wills & Scott 1981; Little & Peggie
1987). There are literally hundreds of described disorders
and injuries in apples. The names and classification of
these disorders are very descriptive and reflect their often
indeterminate and seasonal nature.
The influence of climate and orchard management
on storage disorders
Many storage disorders of apples are associated with
interactions between seasonal climate and mineral nutrition.
