Agriculture Reference
In-Depth Information
(a)
Figure 14.16
Senescent effects from ethylene
exposure to watermelon: tissue disintegration.
(Photo credit: D.J. Huber.)
(b)
air temperature is below freezing, causing fruit loaded
directly under the air outlet to freeze or suffer chilling
injury during transit.
Exposure to various atmospheres
Exposure to ethylene gas during storage or transport can
accelerate senescent processes in nonclimacteric cucurbits.
Premature chlorophyll degradation is induced in cucumber
and zucchini. A 12 hr exposure to 25 ppm ethylene caused
necrotic lesions and decay in Beit Alpha-type cucumbers
within 72 hr at 12
C (Sargent
et al
. 2002) (Plate 14.3). Ripe
watermelon had breakdown of placental tissue when
exposed to extremely low concentrations of ethylene
(1 ppm) (Risse & Hatton 1982). Elkashif and Huber (1988)
reported two- to threefold increases in watermelon electro-
lyte leakage rates and greater breakdown in cell wall ultra-
structure after six days exposure to 50 ppm ethylene at
18
°
Figure 14.17
(a) Internal bruising in 'Galia' melon
due to impact bruising during harvest;
(b) ompression bruise on Beit Alpha cucumber from
protruding surface in carton bottom.
C. They later noted that this same ethylene exposure
accelerated placental senescence in both immature and
mature watermelon (Elkashif
et al
. 1989) (Figure 14.16).
Mature cantaloupe can be treated with exogenous ethylene
(50 to 100 ppm, 24 to 72 hr) after harvest to stimulate uni-
form initiation of ripening (Reid 2002), as is also commer-
cially done for banana, honeydew, mango and tomato.
Exposure to abnormal atmospheres can likewise stress
fruits. Whole and fresh-cut (minimally processed) cucurbits
are increasingly stored in film-wrapped packaging systems.
If the oxygen transmission rate of the film is too restricted,
respiratory activity can produce anoxic conditions, leading
to accumulation of fermentation by-products in the tissues.
°
These by-products initially cause off-flavours and off-
aromas; eventually discolouration and necrosis appear.
With only 24 hours of exposure to elevated (60%) CO
2
levels at 25
C, cucumber respiration and ethylene
production spiked (Mathooko
et al
. 1995), an indication of
tissue stress.
°
Mechanical stresses
Careless handling significantly reduces post-harvest life.
Impact bruises from careless handling stimulate respiration
and ethylene production, hastening senescent processes
such as tissue ripening, softening (Figure 14.17a) and
breakdown of chlorophyll leading to yellowing in
