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

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
182 Postharvest Diseases of Fruits and Vegetables
with an earlier study indicating the marked antifungal activity hidden in
the tissues of this crop (Ark and Thompson, 1959). Among the 49 essential
oils tested, those of palmarosa (Cymbopogon martini) and red thyme
(Thymus zygis) showed the greatest inhibitory effect on J3. cinerea spore
germination at the lowest concentration. The next best inhibitors were
essential oils of clove buds (Eugenia caryophyllata) and cinnamon leaf
(Cinnamomum zeylanicum). The most frequently occurring constituents in
essential oils showing high antifungal activity were: Z)-limonene, cineole,
a-pinene, P-pinene, P-myrcene and camphor. The fungicidal activity of the
individual components, singly and in combination, is being studied (Wilson
et al., 1997b). Essential oil derived from another species of Thymus, T
capitatus, markedly reduced development of S. cinerea in inoculated
mandarin fruit when applied as a vapor. Scanning electron microscope
observations indicated a direct damaging effect of the thyme oil on fungal
hyphae (Arras and Piga, 1994).
Glucosinolates, a large class of compounds produced by plants of the
Cruciferae (Mari and Guizzardi, 1998), are other natural substances with
potential antimicrobial activity. When cells of plant tissues that
metabolize glucosinolates are damaged, these compounds come into
contact with the enzyme myrosinase, which catalyzes hydrolysis. The
antifungal activity of six isothiocyanates, produced by the enzymatic
hydrolysis of glucosinolates, has been tested on several postharvest
pathogens in vitro (Mari et al., 1993) and in vivo on artificially-inoculated
pears (Mari et al., 1996), with encouraging results.
Chitosan is an animal-derived polymer formed by de-acetilation of
chitin. It can serve as a coating for the fruit or vegetable and for regulating
gas moisture and exchange around the product (Wilson et al., 1994). When
applied as a coating, chitosan delayed the ripening of tomatoes and
reduced decay incidence indirectly by modifying the internal atmosphere.
A marked reduction of decay has been recorded in chitosan-treated bell
peppers, cucumbers, strawberries and carrots (Cheah et al., 1997; Wilson
et al., 1994). In litchi fruits, chitosan coating delayed browning of the
pericarp, which is the main problem during prolonged storage (Zhang and
Quantick, 1997). Application of a chitosan coating, in addition to reducing
weight loss of the fruits, delayed changes in the content of antocyanin,
flavonoid and total phenolics, delayed the increase in polyphenol oxidase
activity and partially inhibited the increase in peroxidase activity, which
are associated with tissue browning. This implies that a chitosan coating
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