Temperature Effects on Produce Degradation 639
20.5.3 PEACHES AND NECTARINES
Peaches are generally picked before they reach full ripeness and allowed to ripen
during shipping and/or storage. They will generally become eating ripe in 2 to 4 d
at temperatures of 20 to 27°C.^24 The rate of ripening is about half as fast at 16°C
as at 20°C and about half as fast at 10°C as at 16°C. However, when peaches are
held at 10°C until they are ripe, flavor does not develop normally.
The problem of woolliness or mealiness in peaches and nectarines has long been
recognized as resulting from storage at chilling temperatures.^3 Fruits suffering from
these conditions have a good appearance when removed from cold storage and soften
normally but have dry, mealy flesh texture when they are ripe. Because woolliness
does not affect appearance, it does not become apparent until the fruit is cut.
Storage at 2.2 to 5°C has been shown to result in rapid development of woolliness
symptoms, while storage at 0°C delayed symptom development.^60 Von Mollendorff^61
suggested picking maturity is an important factor in determining whether woolliness
will develop; however, Luchsinger and Walsh^60 found no relationship between matu-
rity stage and woolliness.
Luchsinger and Walsh^60 observed that storage temperature, not water loss, had
the greatest influence on fruit juiciness. Chilling temperatures (0 and 5°C) reduced
the fruit’s juiciness after as little as 7 d in storage, while storage at 10°C maintained
juiciness. Although woolly symptoms developed at 0°C, they took longer to be
expressed than in fruit stored at 5°C. The fruit stored at 5°C showed higher ethylene
evolution rates and faster softening rates.
One strategy proposed to prevent the development of woolliness is to hold the
fruit at ambient temperatures for 36 to 48 h before cooling it to 0°C.^3 The delayed
cooling may lead to slightly more softening during storage than is seen with imme-
diate cooling, but the fruit will soften and become juicy following storage. This
response may be related to the time at ambient temperature allowing the fruit to
maintain its ability to produce ethylene after storage and therefore to initiate normal
ripening. Fruit that is chilled immediately loses the ability to produce ethylene after
a few weeks in storage.
20.5.4 APPLES
The rate of cooling of apple fruit affects retention of quality, but its importance
varies according to variety, harvest maturity, nutritional status of the fruit, and storage
history.^62 Apples respire and degrade twice as fast at 4°C as at 0°C.^63 At 15°C they
will respire and degrade more than six times faster. Most apple varieties are not
sensitive to chilling temperatures and should be stored as close to 0°C as possible.
However, varieties that are susceptible to low-temperature disorders should be stored
at 2 to 3°C. Temperatures also should be increased for fruit stored in low O 2
controlled atmosphere, since lower temperatures increase risk of low O 2 injury. An
additional factor to consider in selecting storage temperatures is the impact of
temperature on RH requirements. It is easier to maintain RH greater than 90% at
1°C than at 0°C.