Agriculture Reference
In-Depth Information
• the frequent need in postharvest handling to expose them to high
temperatures or other stresses during insect disinfestation prior to export.
Respiration is the conversion of sugars such as glucose into carbon dioxide,
water, chemical energy and heat. The chemical energy (ATP, NADH) is used
to synthesize the molecules needed to keep the cells alive and to grow. The heat
represents the inability of the cell to capture fully all the potential energy in
the sugar. The simple overall equation for glucose respiration highlights the
relationship between storage environment and respiration, which is directly
related to postharvest storage life.
Glucose
+
Oxygen
→
Carbon dioxide
+
Water
+
Chemical energy
+
Heat
The respiration rate is decided by the amount of the substrate, in
this equation glucose but it can be starch or fats, and oxygen. The rate of
conversion, indicated by the arrow, is determined by temperature. Lower
storage temperatures lead to a slower rate of respiration and a greater storage
life; the higher the temperature the higher the rate of respiration and the
shorter the storage life. Storage life includes all the time spent in the various
marketing steps from harvest to the consumer.
The initial use of cold to preserve or extend the shelf-life of fresh
commodities in many cultures is lost in antiquity. Examples of the use of cold
for storage of fresh produce range across the use of clamps, cellars, basements,
caves and ice houses. Industries developed around the harvesting of ice in the
winter for use in the summer. The limitations of cold for tropical plants were
well recognized by the 18th century; for example, the Palace of Versailles'
greenhouse was designed to keep tropical plants alive during winter. An
understanding of the range of suitable temperatures for fruits and vegetables
followed the development of reliable calibrated thermometers in the 1700s by
the Dutch instrument maker Gabriel Fahrenheit and the Swedish astronomer
Anders Celsius. The choice and acceptance of common fi xed temperature
points (freezing and boiling points of pure water) led to standardization of
temperature scales.
Climacteric and non-climacteric
Like temperate fruits, tropical fruits can be divided into climacteric and non-
climacteric (Table 5.1). This division is based on the respiratory pattern after
harvest. In climacteric fruits such as banana and papaya, there is generally
a dramatic and rapid change in respiration, ethylene and other quality
characteristics during ripening. In commercial handling, ethylene can lead
to earlier ripening of climacteric fruit but not of non-climacteric fruit. Non-
climacteric fruit such as pineapple and citrus should be already ripe and ready
to eat when harvested since they show little change in respiration and quality
characteristics after harvest.
