V. POSTHARVEST LIFE
It should not be necessary to emphasize that fruits are still alive after harvest. However, a surprising num-
ber of people who make their livelihoods growing, packing, shipping, and selling fruit do not realize that
they are handling living, breathing creatures, subject to specific diseases and the ravages of senescence.
(“Gee, Doc, don’t tell me these things are alive. They’ve been picked!”) Moreover, effective postharvest
handling is not merely a matter of maintaining the state of fruit quality at the time of picking. Properly
handled, many fruits improve in eating quality after harvest. Others degenerate rapidly or slowly, de-
pending on their innate physiology and the postharvest conditions to which they are subjected.
A. Climacteric Versus Nonclimacteric Fruits
The first step in proper postharvest handling of a given type of fruit lies in understanding its type of life
cycle [49]. The climacteric rise in respiration of fruits such as apple, pear, avocado, mango, and banana
represents a rapid depletion of potential postharvest life (Figure 6). For fruits such as pear, banana, and
avocado, experiencing the climacteric is essential to the ripening that makes them truly edible. But it
should be delayed as much as possible until the consumer is ready to eat that piece of fruit. Very prompt
refrigeration is essential for orderly marketing of climacteric-type fruits, to delay or suppress the evolu-
tion of endogenous ethylene that initiates the climacteric rise. As the height of the climacteric is reduced,
its duration is extended proportionately. Immediate temperature and humidity control is the first line of
defense against expensive wastage. Humidity control is important if for no other reason than that a shriv-
eled fruit ceases to be marketable. However, there are other physiological benefits also [50]. Even within
a specific variety, response to such storage techniques as controlled atmosphere storage can be sharply in-
fluenced by cultural and climatic factors [51]. When the peak of the climacteric rise is past, the fruit be-
comes senescent. Although adequate reserves of respiratory substrate may be available, cellular organi-
zation breaks down, the cell membranes lose their integrity, and the fruit dies of old age [52,53]. Thus the
challenge with climacteric-type fruits is to suppress and extend the respiratory rise.
Apples and pears are examples of climacteric-type fruits that have to be harvested within a very brief
period but marketed for as long a period as correct storage procedures permit. Long-storing varieties have
ample reserves of respiratory substrate and resilient respiratory systems. Under near-optimum conditions,
late varieties such as Winesap can be kept year-round. Some, such as Northern Spy and Winter Banana,
improve in eating quality during the first few months of storage.
The avocado (Persea americana) is an interesting climacteric-type fruit. Although strongly climac-
teric, the characteristic respiratory rise will not start until the avocado is picked. For many years research
workers were convinced that when their instrumentation improved sufficiently, they would be able to
identify a preharvest “climacteric inhibitor.” Even with modern equipment, it has been impossible to iden-
tify any such inhibitor [54].
154 GRIERSONFigure 6 Climacteric and nonclimacteric life cycles for typical fruits. (From Ref. 34.)