Post harvest diseases fruits and vegetables - Xavier University ...

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
204 Postharvest Diseases of Fruits and Vegetables
Non-pesticide chemicals can also improve the effectiveness of heat
treatment. The addition of sucrose to hot water (52°C) reduced the
external discoloration of peaches and nectarines, which usually appears
under shelf-life conditions, following heat treatment. In fact, the addition
of sucrose enabled heat to be used to control decay in these fruits
(Barkai-Golan and Phillips, 1991). The action of sucrose is not yet clear,
but it is possible that the sugar slows hydration of the fruit surface
exposed to the hot water, or protects this surface in some other way.
Enhanced efficiency of heat treatment in maintaining fruit firmness
and reducing storage diseases can be achieved by combining heat and
calcium treatments after harvest. Whereas immersing apples in water at
45°C reduced Gloeosporium decay, but increased tissue breakdown, the
addition of CaCh to the hot water controlled tissue breakdown and
suppressed decay development (Sharpies and Johnson, 1976). Later
studies with combined treatments showed that long-term heating (38°C,
4 days) of Penicillium expansum- or Botrytis cmerea-inoculated Golden
Delicious apples followed by pressure infiltration of 2 or 4% CaCb
solution, elicited accumulative or synergistic effects in retarding both
softening and decay development during cold storage and shelf-life
conditions (Conway et al., 1994c; Sams et al., 1993).
In another study with Golden Delicious apples, Klein et al. (1997)
found that infections resulting from pre-storage inoculations of the fruit
with B. cinerea spores were controlled only by a subsequent 4-day
exposure to 38°C, and that neither 42°C for 1 day nor Ca treatment were
effective in preventing decay during storage. Combining Ca infiltration
(2% CaCl2) with 38°C heat treatment had no advantage over heating
alone but resulted in increased decay development. It was suggested that
the pressure infiltration with CaCk solution may have carried some
B. cinerea spores further into the wound beyond the "zone of protection"
afforded by the heat treatment (Klein et al., 1997). Furthermore, holding
apples at 38°C for 4 days before Ca infiltration, decreased the amount of
Ca taken in. The decreased intake of Ca may have been the result of a
flow of epicuticular wax during heating, resulting in the sealing of
surface cracks through which CaCh solution might have entered the fruit
(Roy et al., 1994).
A combination of heat with ionizing radiation has been found to be
more effective than either means separately, in reducing various
host-pathogen interactions, including oranges infected by Penicillium
digitatum (Barkai-Golan et al., 1969), nectarines infected by Monilinia
fructicola (Sommer et al., 1967), mangoes infected by Colletotrichum
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