Agriculture Reference
In-Depth Information
(a)
Figure 14.15
Freezing injury in epidermal tissue in
summer squash (center fruit).
during subsequent storage at 10°C over cucumbers grown
at 27°C. Small, round watermelons that received a precon-
ditioning treatment (3 days at 26°C) prior to storage at 1°C
had fewer chilling injury symptoms than those not receiv-
ing the pre-treatment (Risse
et al
. 1990). Honeydew mel-
ons exposed to high solar radiation accumulated more
unsaturated lipid fatty acids in epidermal tissue (Forney
1990) and lower amounts of ACC (1-aminocyclopropane-
1-carboxylic acid, a precursor of ethylene) (Lipton
et al
.
1987), possible reasons for induced tolerance to otherwise
chilling temperatures.
Transgenic Charentais melon fruit were developed
which produced almost no ethylene. Ethylene was impli-
cated as contributing to chilling injury; these melons
developed no chilling injury during 3 weeks storage 2°C,
whereas wild-type fruit developed chilling injury
( Ben-Amore
et al
. 1999). When treated with ethylene at
ambient temperatures, the transgenic fruit later developed
chilling injury symptoms during storage.
Zucchini squash exhibited less visible chilling injury
symptoms when stored at 2.5°C and in low oxygen (4%),
however after transfer to air at 10°C for 2 days, chilling
injury symptoms developed. Severe off-flavours developed
after storage at 2.5°C or 10°C; some were even more
apparent after cooking (Mencarelli
et al
. 1983).
Freezing injury can occur in the field or during shipping
and handling. It is distinguished from chilling injury in
that frozen tissues appear necrotic, water soaked and flac-
cid, generally covering larger areas of the fruit surface
and extending into the flesh, depending upon severity
(Figure 14.15). Formation of intercellular ice is the main
cause (Kays, 1991). Freezing injury can occur during
shipping in refrigerated trailers that have top air delivery.
In these systems, refrigerated air is blown to the rear of the
trailer via a ceiling duct (or, 'air chute'). Often the outlet
(b)
Figure 14.14
Poor pollination can lead to misshapen
fruit (a) and, in severe cases, the formation of
internal cavities (b).
developed surface pitting and had increased water loss dur-
ing storage at 2°C; after 3 days storage this stress stimulated
ethylene evolution (from virtually undetectable to 1.5 nl/g-hr),
and after 6 days respiration also increased (McCollum
1989). Internal tissues can also be affected by chilling
injury, such as necrotic tissue below the epidermis of yellow
summer squash and discolouration of mesocarp tissue in
cantaloupe.
Seedless watermelon fruit were susceptible to chilling
injury during storage at 1°C (Risse & Maynard 1990).
Warm temperatures can impart some resistance to chilling
injury. Kang
et al
. (2002) reported that greenhouse-grown
cucumbers at average daytime temperatures of 32°C were
more resistant to chilling injury and remained firmer
