Produce Degradation Pathways and Prevention

Temperature Effects on Produce Degradation 613

water loss from the products, and less development of decay caused by pathogens.
Harding and Haller^21 demonstrated that harvested peaches held at 23°C lost firmness
at a rate of 3 to 4 pounds per day as measured by a Magness-Taylor pressure tester
(5/16-inch^ tip). If the fruit was harvested at 14 pounds firmness, it softened to 2 lbs
in just 3 to 4 d. At cooler temperatures, near 0°C, the softening was only a fraction
of this rate. As a general rule, more quality is lost in 1 h at 20°C than in 24 h at 0°C.^3
As calculated for Q 10 , the generally accepted rule is that the respiration rate of
fruit is doubled or tripled for each 10°C rise in temperature. This means that fruit
ripens two to three times faster at 10°C than at 0°C and two to three times faster at
20°C than at 10°C.^22 Thus, it is critical that fruit is cooled to storage temperatures
as quickly as possible (Figure 20.3). For example, assume that apples are put into
storage at 20°C and are cooled to a holding temperature of 0°C in 1 week. The
cooling of these apples involves holding the fruit at 20°C for 4 d and then dropping
the temperature to 10°C and holding the fruit for 3 d before the final drop to the
0°C holding temperature. The first 4 d at 20°C are comparable to 28 d at 0°C and
the 3 d at 10°C are comparable to 6 d at 0°C. In other words, the storage life of
apples cooled under these conditions is shortened by 34 days. The conditions would
not be quite so extreme in actual practice since the cool-down would actually start
immediately, so a 4-d holding period at 20°C would probably not occur. However,
apples are often brought into storage at temperatures higher than 20°C.
Precooling is commonly used to refer to any cooling treatment before shipping,
storage, or processing.^2 A stricter definition is “cooling methods by which produce
is cooled rapidly, generally within 24 hours of harvest.” A number of methods are
in use for precooling fruits and vegetables; however, the two most commonly used
methods are cold air cooling and hydrocooling.

FIGURE 20.3Normal storage life expectancy for Delicious apples when cooled at different
rates and stored at different temperatures. (Adapted from Bramlage, W. J. and Morris, J. R.,
Storing apples, in Modern Fruit Science, 10th ed., Childers, N. F., Morris, J. R., and Sibbett,
G. S., Eds., Horticultural Publications, Gainesville, FL, 1985., Chap. 11.)

HELD AT 2°C TO DEC. 20

HELD AT 2°C TO JAN. 6

HELD AT 4°C 21 DAYS; THEN TO 0° IN 28 DAYS; HELD 0° TO FEB. 10

THEN COOLED TO 0°C IN 4 WEEKS; HELD AT 0°C TO MAR. 20

HELD AT 0°C TO APR. 15

HELD AT -1°C TO JUNE 1

COOLED TO 2°C

IN 6 WEEKS

COOLED TO 2°C

IN 7 DAYS

COOLED TO 4°C

IN 7 DAYS

COOLED TO 2°C

IN 7 DAYS

COOLED TO 0°C

IN 7 DAYS

COOLED TO -1°C

IN 7 DAYS

SEPT. OCT. NOV. DEC. JAN. FEB. MAR. APR. MAY