Advancements in Oil and Oilseed Processing - Food and Industrial Bioproducts and Bioprocessing - page 113

4.2 OILSEED PRETREATMENT
4.2.1 Handling and storage
Oilseeds are shipped in railroad cars, trucks or barges for ship transportation. Seeds are received
and stored at elevators. The physical properties of the seeds, such as size, shape, bulk density
and flow characteristics, affect the design of oilseed handling facilities. For example, canola,
rapeseed, delinted cottonseed, soybean and sunflower have very good flow properties. They are
usually stored in vertical storage bins. Copra and undelinted cottonseed do not flow well. Hence,
vertical bins are not suitable for these types of seeds. Copra is stored in large flat warehouses.
Storage bins can be built of stainless steel, concrete, brick or other materials. Stainless steel bins
are preferred where ambient temperature is low while concrete bins are built at places where
average outside temperature is relatively high (35-45°C) (Berger, 1985). Some oilseeds are
abrasive, and abrasion-resistant materials need to be used on seed contact surfaces.
Proper handling and storage of oil-containing materials are very important to minimize
deterioration and maintain good quality of both contained oil and meal. Whole, intact
low moisture oilseeds (about 8-10% moisture) may be stored for extended time under
suitable conditions. Deterioration of oilseeds is accompanied by respiration or carbon
dioxide evolution and heat generation by oxidation reactions. Damaged and high moisture
seeds may release higher amounts of carbon dioxide than sound and intact seeds (5 vs.
0.1 cubic centimeter or more of carbon dioxide per gram of seed per day) (Rukunudin
et al ., 2004 ; Mattil et al ., 1964). Furthermore, heat generation by oxidation reactions
may increase the temperature of the stored seed, accelerating deterioration even to the
point of charring the seeds.
Activity of native enzymes present in oilseeds, infestation by insects and mites along
with microbial activity during storage are also important factors affecting oil and meal
quality. If microbial growth occurs it is accompanied by production of metabolites and
mycotoxins, particularly aflatoxins. Aflatoxins produced by strains of Aspergillus flavus
emerge partly in the expressed oil. In such a case oil requires further refining for aflatoxin
removal. Aflatoxin-containing meal is also unsafe as animal feed.
In general, high moisture content in seeds (above 14-15% moisture) and high relative
humidity conditions accelerate lipolytic enzyme reactions and increase the free fatty acid
(FFA) content in oils. Oil in mature seeds may contain about 0.5% FFA. However, if seeds
are damaged mechanically or by frost or become wet during harvest, handling and storage,
the acidity of oil can be much higher. Sprouting, which is considered a damage factor, is
another important issue during storage of high moisture seeds. Sprouted seeds may have
lower oil and higher FFA content compared to sound seeds (Mostafa et al ., 1987 ).
Today, air dryers are essential components of modern storage facilities to maintain
oilseed quality. Most oilseed storage bins are equipped with aeration ducts and ventilation
blowers to cool the seeds. Since oxidation reactions are aerobic processes, a low oxygen
atmosphere in storage bins helps to slow down oxidation and quality deterioration. Mature
seeds can be stored longer than immature seeds because of the lower activity of oil-splitting
enzymes in mature seed. Proper storage of harvested oilseeds may also contribute to
desirable changes. For example, oil extraction yields from fresh soybeans can be lower than
for soybeans stored more than five months. The storage of soybeans also decreases
chlorophyll content of green beans (Gomes et al ., 2003 ; Mattil et al ., 1964 ).
Logistical implications of transportation and handling of genetically modified oilseeds
are particularly important. Bioengineered oilseeds with enhanced quality attributes need to