The literature abounds in such examples. Many mysteries would be elucidated if research work-
ers routinely reported temperatures (whether controlled or not) and included such data in their research
reports. Subsequent research workers, if alert to the multitudinous roles of temperature, will then be
in a position to carry the research further, perhaps with the advantages of better funding or instru-
mentation.
III. POSTHARVEST ROLE OF TEMPERATURE
A. Handling, Storage, and Shipping Temperatures
It is all too often forgotten that crops are still alive after harvest. No matter how meticulously grown,
most horticultural crops will not realize their full economic or nutritional potential unless handled at
suitable temperatures after harvest. How important this is depends on both the frailty of the crop and
time between harvest and consumption or processing. During this period, the importance of tempera-
ture and humidity depends very largely on the biological maturity of the plant part being harvested
[101]. Temperature control is obviously of more consequence for asparagus than for coconuts. Only a
very brief account of the principles involved can be given here. Attention is drawn to the U.S. Depart-
ment of Agriculture handbook dealing with storage conditions for a very wide range of produce [102].
Most agronomic crops are far less sensitive to postharvest temperatures, but there are exceptions, such
as potatoes (see Sec. III.D).
- Fruits
Chapter 7 deals with the development and physiology of fruits, which, botanically, can mean any ma-
tured plant ovary from a grain of wheat to a watermelon. Thus, the comments here are very brief and are
largely confined to temperature relationships of dessert fruits that are sometimes processed but more tra-
ditionally are eaten fresh. Bear in mind, however, that many products considered to be vegetables are
botanically fruits: tomatoes, green (snap) beans, squash, bell peppers, and cucumbers are all botanically
fruits.
Fruits can be classified according to their respiration pattern as climacteric or nonclimacteric [103].
Soon after harvest, climacteric fruits (e.g., apples, pears, bananas) produce ethylene in quantities suffi-
cient to overcome the antidoting effect of internal carbon dioxide [104]. The result is a rapid rise in res-
piration rate, at the conclusion of which the fruit is senescent, overripe, and unpalatable. The useful life
of a climacteric-type fruit is typically ended by senescence rather than by decay. Prompt refrigeration is
thus critical for climacteric-type fruits. The more the climacteric rise in respiration can be suppressed, the
longer the postharvest life of the fruit.
Nonclimacteric fruits (e.g., citrus and grapes) have no climacteric rise in postharvest respiration. At
any constant temperature, their respiration rate remains constant. For such fruits, refrigeration functions
more to prevent or delay the onset of decay than to lower respiration rate. For any type of fruit, one of the
major functions of temperature regulation is to maintain fruit quality. This involves control of desicca-
tion, minimization of flavor and texture loss, and prevention of off-flavors.
Selection of optimum storage temperatures for some fruits can be conditioned by susceptibility to
chilling injury (see Sec. III.C). Particularly for long-term storage, avoidance of chilling injury can over-
ride considerations of respiration rate or decay.
Prevalence of storage disorders such as water core [105] and superficial scald [106] of apples can be
affected not only by storage temperature but also by preharvest growing temperatures. Chemical compo-
sition of Satsuma mandarins varies with growing temperature [107]. Production of high-quality, low-acid
grapefruit depends on uninterrupted warm winter night temperatures [108].
- Seeds
Storage temperature and thus potential storage life are sharply conditioned by the tolerance of seeds to
desiccation. “Orthodox” seeds that will survive desiccation (and often will desiccate on the plant) can be
stored at very low (subfreezing) temperatures. “Recalcitrant” seeds that cannot survive desiccation are
very difficult to store because they cannot survive low temperatures. These brief remarks oversimplify a
complex situation. Readers needing to know more are referred to a very detailed review article by Ellis
[41].
26 GRIERSON