600 Produce Degradation: Reaction Pathways and their Prevention
20.5.7 Tomatoes ..................................................................................... 641
20.5.8 Fresh-Cut Produce ...................................................................... 642
20.6 Summary .................................................................................................... 643
References.............................................................................................................. 643
20.1 THE NEED FOR TEMPERATURE MANAGEMENT
Good temperature management is the single most important factor in determining
the ultimate quality of fresh fruits and vegetables. All fresh produce are living
organisms and, for optimum quality, must remain alive and healthy until they are
processed or consumed. Plant material can live only as long as the membrane
structure and enzymes remain functional. Exposure to undesirable temperatures,
either above or below the optimal range for this functioning, results in many phys-
iological disorders. Temperature also influences the rate of ethylene production and
utilization as well as the rate of spore germination and growth rate of pathogens.
Temperature extremes can cause changes in the functions of the plant tissues, many
of which lead to quality loss through product degradation.
In order to maintain the highest possible produce quality, it is necessary to slow
respiration and, therefore, product deterioration processes as much as possible.^1 One
way to do this is to lower the temperature. As a general rule, each 10°C reduction
in temperature lowers respiration rate by a factor of 2 to 4. This can have a significant
effect on the keeping quality of produce. For example, an apple or a pear will ripen
as much in a day at 21.2°C as it will in a week at 0°C.^1
Because various fruits and vegetables respond differently to temperature, there
is no one ideal temperature for the storage of all produce. However, the many positive
effects of lowered temperatures lead to extensive use of cool storage to restrict deteri-
oration without causing abnormal ripening or other undesirable changes (Figure 20.1).
In fruits and vegetables not susceptible to cold injury, maximum storage life can be
obtained by storage close to the freezing point of the tissue.^2 For chilling-sensitive
produce the advantages of reduced respiration and fungal growth must be balanced
against potential losses from chilling injury. Table 20.1 and Table 20.2 show the
recommended storage temperatures for a variety of fruits and vegetables. The tem-
perature in a storage room should be kept within 1oC of the desired temperature for
the produce being stored.^3 Temperatures above the optimal range can shorten storage
life; temperatures below the optimal range can cause chilling or freezing injury.
20.2 EFFECTS OF TEMPERATURE
20.2.1 RESPIRATORY ACTIVITY AND STORAGE LIFE
The energy for life processes comes from the food reserves that are accumulated
while the commodities are still attached to the plant. The process of converting the
food reserves to energy is respiration. Some of the energy produced by respiration
goes to maintain life processes and, therefore, to slow degradation. In general, there
is an inverse relationship between respiration rate and storage life.^2 Therefore, a
product with a low respiration rate usually keeps longer. It is widely accepted that