Agriculture Reference
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the wall. Due to high pressure, a progressive breakage of the cell walls was observed, which
allows the free transfer of the fatty acid chains from inside the cells (Femenia et al., 2001).
8.12.2 Heat
Postharvest heat treatments lead to an alteration of gene expression, and fruit ripening
can sometimes be either delayed or disrupted. Cell wall-degrading enzymes and ethylene
production are frequently the most disrupted, and their appearance is delayed following
heating. Fruit sensitivity to heat treatments is modified by preharvest weather conditions,
cultivar, rate of heating, and subsequent storage conditions (Paull and Chen, 2000). Prestor-
age heat treatment appears to be a promising method of postharvest control of decay. Heat
treatments against pathogens may be applied to fresh harvested commodities by hot water
dips, by vapor heat, by hot dry air, or by a very short hot water rinse and brushing.
Banana fruit exposed to elevated temperatures showed increased softening, and soften-
ing was inhibited by 1-MCP treatment, which suggests that heat enhances synthesis of new
ethylene sites which mediated banana fruit softening (Jiang et al., 2002)
In case of apple
slices, the heat treatment inhibited slice texture changes but reduced sensory firmness (Bai
et al., 2004).
In strawberries, heat treatments reduced EGase and
.
-Xyl activity and delayed hemi-
cellulose degradation. The application of heat treatment affected the solubization of pectins
and hemicelluloses. PG and
β
-Gal activity was also inhibited by heat treatment, but PME
activity was enhanced (Vicente et al., 2005).
PG and xylanase decreased in papaya by hot water treatment (49 C for 120 min), and
dissolution of the middle lamella and destruction of the cell wall were inhibited (Bacay-
Roldan and Serrano, 2005). PG, which was altered by vapor heat treatment, influenced the
development of physiological injury in papaya (Suzuki et al., 1994).
Heat treatment inhibits the synthesis of cell wall hydrolytic enzymes (Schirra et al.,
2000). Prestorage heat treatment could delay the ripening of “Gala” and “Golden Delicious”
apples and maintain storage quality (Shao et al., 2007). Heating “Golden Delicious” apples
for 4 days at 38 C reduced decay and maintained fruit firmness during 6 months of storage
at 0 C (Sams et al., 1993).
Cooking resulted in an increase in the water-soluble pectins and a decrease in the pectins
associated with cellulose. The total cell wall polysaccharide and galactose content of the
squash cultivars remained unchanged for up to 2 months of storage and decreased later
(Ratnayake et al., 2003).
β
8.12.3 Physiological disorders
Symptoms of water soaking in watermelon were accompanied by increases in the levels
of water- and CDTA-soluble polyuronides and significant molecular mass downshifts in
polyuronides in both immature and ripe fruit (Karakurt and Huber, 2002). Catabolic reac-
tions targeting the cell walls contribute to the development of water-soaking disorder in
watermelon, and PG, EXP, LOX, PLC, and PLD levels increase with its onset and devel-
opment (Karakurt and Huber, 2004).
Depolymerization of high-molecular-mass trans- 1,2-CDTA-soluble pectin occurred
in severely watercored pear fruits, but there were no such metabolic changes in the
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