Temperature Effects on Produce Degradation 619
(Ceratitis capitata) are to expose fruit to 0°C for 10 d, 1.1°C for 12 d, 1.7°C for
14 d, or 2.2°C for 16 d. However, many fruits suffer chilling injury at these temperatures.
20.4.1 CHILLING INJURY
20.4.1.1 Occurrence
Low temperatures are the most effective means of extending the shelf life of many
commodities. However, some commodities are “chilling-sensitive” in that they suffer
injury when cool-stored at temperatures above their freezing point. The term chilling
injury is used to refer to both the physiological response of the tissue to the low
temperature and the resultant symptoms that affect product acceptability.^4 It can occur
in the field, during transportation, during storage, during wholesale distribution, in the
retail store, and in the home refrigerator. Synonymous terms include chilling damage,
chilling disorders, low-temperature breakdown, and low-temperature disorders.
Commodities experiencing chilling injury were once thought to be tropical or
subtropical crops, since these materials are acclimatized to fairly high temperature
and intolerant of low temperatures. However, crops of temperate origin have also
been found to develop physiological disorders when exposed to low temperatures.^27
Among the temperate-zone fruits susceptible to chilling injury are apples, cranber-
ries, peaches, nectarines, and plums.
Chilling injury is thought to occur in distinct phases.^28 First, there is the primary
response to temperature, usually considered physical in nature, such as membrane
alterations. Next, physiological changes occur. Although short-term exposure to
chilling temperatures may produce reversible changes, if exposure is continued the
changes become harmful and result in the development of symptoms.
Both temperature and duration of exposure are involved in the development of
chilling injury.29,30 In tropical fruits such as bananas, severe injury occurs after
exposure to chilling temperatures for only a few hours, and all fruits in a sample
suffer injury. In commodities such as apples and grapefruits, injury can take weeks
or months of chilling to develop and may be seen only in part of a chilled sample.
FIGURE 20.8Hydrovac coolers minimize moisture loss due to evaporative cooling by spray-
ing produce with water either before the cooling process or towards the end of the vacuum
operation. The photo on the left shows produce arriving at the cooling facility. The photo on
the right shows produce being loaded into a hydrovac cooler. (Photos courtesy of Western
Cooling Systems, Fremont, CA.)