Fruits and Pulses
Vegetables as a group of food plants also include some fleshy fruits
(tomato, cucumber) and immature fruits (e.g., peas and bean pulses).
Compared with most vegetables, postharvest storage of fleshy fruits
shows both similarities and differences. The function of a fruit—quite
different from that of vegetables—is to protect the developing seeds
against predators and later to attract the same predators (animals or hu-
mans) in order to secure seed distribution. This means that the physio-
logical basis for storage and shelf life of fleshy fruits is closely associated
with their maturation and subsequent ripening and senescence.
Fruit can be classified either as climacteric or nonclimacteric due to
the pattern of respiration and ethylene production during ripening. Cli-
macteric fruit are characterized by a transient increased rate of respira-
tion and ethylene production with the magnitude varying considerably
between fruit species. Fruit with a narrow respiratory peak may change
from unripe to overripe within a few days when kept at room tempera-
ture, while fruit with a wider peak may remain ripe for several days or
weeks. During the growing period, most climacteric fruit accumulate
starch, which is then degraded to soluble sugars during ripening pro-
viding both sweetness to the fruit and substrate for respiration and syn-
thesis of, e.g., pigments and aroma compounds.
Nonclimacteric fruit ripen without any increase in the rate of respira-
tion and ethylene production. Since these fruits do not accumulate starch,
their sweetness is dependent on the ability of the plant or tree to export
carbohydrates to the fruit during the period preceding harvest. This means
that harvesting of nonclimacteric fruits must be delayed until the fruit
has reached full ripeness. While most climacteric fruits intended for stor-
age or distribution over long distances must be harvested preclimacteric,
those with a nonclimacteric ripening may be harvested ripe and often
stored for several weeks without any change in eating quality.
Biennial Vegetables
Vegetables belonging to this group normally complete their life cycle
over a two-year period but low temperatures during the seedling stage
may, depending on species and cultivar, result in vernalization and
sprouting already in the first year. Normally, some kind of storage organ
is developed in the first season of growth followed by flowering and
seed formation with subsequent tissue death in the second year. Mor-
phologically, biennial vegetables can differ considerably—from a stor-
Physiological Basis for Postharvest Quality Maintenance 99