Field Guide of Discovery-based Exercises for - Aseanipm ...

Section 7 • Participatory Plant Breeding, Seed Production, Harvest, and Post-Harvest Management
• Oxygen and carbon dioxide. Oxygen (O 2 ) and carbon dioxide (CO 2 ) also influence respiration
rate within immediate vicinity of the commodity. Since O 2 is a reactant of respiration, by law of
mass action, a decrease of O 2 from 21 % will slow down respiration rate. Too low concentration
of O 2 , however, will result in fermentation, giving produce a fermented odor, an off-flavor,
which is not desirable.
On the other hand, since CO 2 is a product of respiration, an increase of CO 2 from 0.03 % will
result in a decrease rate of respiration up to a certain point. Too much accumulation of CO 2 ,
results in CO 2 injury, as manifested by symptoms like discoloration, off–odor, and off-flavor.
A decrease in O 2 and an increase in CO 2 in immediate vicinity of a commodity, therefore means
increased storage life. However, a very low amount of O 2 or a high level of CO 2 in a container
of produce results in rapid decline in quality.
• Relative humidity. Temperature and relative humidity primarily controls the rate of decline in
water reserves. The cells of most vegetable produce contain very high amount of moisture. If
relative humidity of atmosphere is low, the tendency is for cells to lose water to the atmosphere.
Hence, for most produce, higher temperature and lower relative humidity result in faster water
loss. Consequently, shriveling occurs.
At a given temperature, lower relative humidity causes faster transpiration and consequently
faster shriveling of produce. High temperature aggravate low relative humidity. Vegetables are
best stored at high relative humidity (e.g., 80-95%), but produce should be healthy, containers
as well as storage space should be clean because microorganisms multiply very fast under high
relative humidity.
• Injuries. Injuries serve as avenues for entry of microorganisms and easy exit of water from
produce. Even if no wound is visible, cells might have been ruptured during careless handling.
Fast deterioration of injured cells is a result of evolution of ethylene, faster rate of respiration,
and transpiration of injured cells as a response to injury. High levels of ethylene speed up
ripening, causes green produce to turn yellow, and root vegetables to sprout. Therefore, injuries
have to be kept to a minimum, if not entirely avoided.
In FFSs, innovative experiences in post-harvest handling and primary processing of crucifers and
other vegetables must be shared among farmers to further improve their existing practices. The
foregoing exercise was specifically designed to achieve this purpose.
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