Structure and Function of Complex Carbohydrates in Produce 585
leaves as well as a decrease in firmness and crispness, was found to be associated
with changes in cell wall carbohydrate metabolism. Furthermore, the product quality
was closely related to cell wall polysaccharides and textural properties [180].
Various strategies that plants adopt in response to environmental stresses have
been studied in detail [181]. Elevated temperatures, for example, generally known
to contribute to flesh softening, increase the soluble solids (polysaccharides) content
and change the flesh color [182,183]. Because carbohydrates degrade at a faster rate
at higher temperatures, postharvest losses are much higher at ambient temperatures
[184]. Low levels of chlorophyll accompanied by high chlorophyllase activity were
also observed in apples stored at ambient temperatures compared to apples stored
at refrigerated temperatures [185]. Interestingly, contrary to the deleterious effects
of high temperatures on produce, some investigators found that cucumbers grown
in a greenhouse at elevated temperatures during the day could increase their tolerance
to postharvest chilling [186].
Preharvest exposure of fruits and vegetables to direct sunlight, with associated
high tissue temperatures, can result in differences in internal properties such as sugar
content, tissue firmness, oil levels, and mineral content. Fruits with different tem-
perature histories respond differently to postharvest treatments. For example, avo-
cado fruit from exposed sites on a tree have less chilling injury, whereas in citrus
and persimmons chilling damage is more pronounced in exposed tissues [187,188].
Cycles of intermittent warming for 1 d at 20°C every 6 d of postharvest storage
were found to be useful in maintaining the cellular integrity in peaches during
ripening [189].
19.5 STRATEGIES TO MINIMIZE POSTHARVEST
DAMAGE TO CARBOHYDRATESGenerally, many efforts have proven to be quite useful in delaying or minimizing
the damage caused by postharvest stresses. However, only the few approaches that
affect the polysaccharides are mentioned here. Some studies have shown that the
surface coating of fruits has been very effective in improving the storage time,
delaying carbohydrate degradation, and preventing infections. In this regard, coating
several varieties of pears with a carnauba-based wax emulsion suppressed ripening,
reduced the incidence of senescent breakdown, greatly improved the finish of the
skin [190], and protected fruits against wound pathogens [191]. Chitosan treatment
of tomatoes inhibits the growth and the production of pathogenic factors by black-
mold rot [192]. Surface coatings have also been effective in preventing the loss of
bioactive compounds in highly perishable fruits and vegetables. For example, a starch
coating prevented the loss of soluble pectins in radishes [138,193–195].
Exposure to various gases and chemical agents also affects storage and ripening
in fruits. For example, ripening in kiwifruits is accompanied by softening of tissues
and an increase in soluble solids (polysaccharides). A 2-week exposure to high levels
of carbon dioxide substantially lowered the soluble solids production for up to 8
weeks. This effect, however, lasted only for a week when kiwi fruits were stored at
20°C [196]. Postharvest storage of tomatoes under nitrogen for 35 h, under low