Chemical Changes In Storage
Stored soybeans may undergo physical,
physiological and chemical changes even under
ideal storage conditions. Some of the changes
may or may not have a negative effect on the final
use of soybeans and soybean meal depending
on the degree of change. One common indicator
of chemical change in stored soybean is the level
of free fatty acid (FFA) present. An increase of
FFA above 1% may translate into lower quality
of its oil content. The effect of temperature and
moisture on FFA content in soybeans is shown
in Figures 9, 10 and 11. Other important changes
include decline in soybean seed viability, change
in the grain color, increase or decrease in its
moisture, decomposition of phospholipid, and
the denaturation of it protein. Soybean grain is
more resistant to deterioration during storage than
soybean meal. Full-fat soybean meal deteriorates
more rapidly than defatted meal because of its
higher oil content.
The graphs clearly show that high storage temperatures and soybean moisture contents above 10.5%
results in increased FFA content of oil above acceptable levels of less than 1%. These findings indicate
the need to keep the temperature and moisture content of stored soybeans as low as possible and
use it before the FFA content in its oil exceeds acceptable levels.
These conditions agree with the storage requirements that limit growth of insects and molds in stored
soybeans (see the mold envelope and seed wet-bulb temperatures in Figure 6). At a moisture level
of 10.5% or less, soybeans can be stored at any ambient temperature without molding problem.
However, insects may still grow and multiply at relative humidities above 60%.