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

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
88 Postharvest Diseases of Fruits and Vegetables
lignin formation. Thus, holding the fruit at this temperature facihtated
decay development. On the other hand, lowering the relative humidity
below 75% dried up the cells around the wound, and such injured cells
were incapable of lignin production (Brown, G.E., 1973). In an earlier
study, the infection resistance of unripe papaya fruits was similarly
attributed to the ability of the tissue to produce lignin, which prevented
fungal progress within the tissue (Stanghellini and Aragaki, 1966).
Decay reduction has also been achieved through the curing and
lignification of superficial wounds in the peel of citrus fruits, by using
plastic film to seal-package individual fruits for 1-3 days at high relative
humidity and moderate or high temperatures (32-36°C) prior to storage
(Brown, G.E. and Barmore, 1983; Eckert et al., 1984; Golomb et al.,
1984). Healing of wounds under these conditions was attributed to the
water-saturated atmosphere formed within the plastic wrap. The
water-saturated atmosphere, when applied together with high
temperatures, in addition to retarding tissue aging and preserving the
integrity of all membranes, may also stimulate the biosynthesis of lignin
by the living cells surrounding the wound. Under these conditions,
lignification results in a considerable reduction in decay incidence,
without affecting the taste of the fruit (Ben-Yehoshua et al., 1987).
Wrapping various citrus fruits (lemon, orange, grapefruit and pomelo)
in sealed plastic film protects them from damage caused by the high
temperature; the optimal temperature and duration of curing can be
determined for each fruit/fungus system (Ben-Yehoshua et al., 1988).
(Figs. 16, 17).
In more recent studies Stange and Eckert (1994) indicated that
improved decay control in lemons could be achieved by dipping the fruits
in a surfactant solution, prior to curing at 32°C in a water-saturated
atmosphere. The enhanced decay control was probably due to the
increased mortality of P. digitatum conidia and germ tubes. In other
studies with citrus fruits, however, Stange et al. (1993) came to the
conclusion that the evidence for the involvement of lignin in wound
protection in citrus fruits was based on histochemical tests which were
not entirely specific for lignin; they suggested that the resistance of the
wound to infection had to be attributed to the deposition of induced
antifungal gum materials, rather than lignin, in the resistant wound. In
support of this hypothesis, Stange et al. (1993) presented the finding that
extracts from hardened, resistant wounds contained several induced,
low-molecular-weight aldehydes, some of which had marked antifungal
activity. The resistance of the wound to infection may be associated
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