Page 397 - Biosystems Engineering

374 Cha pte r T h i r tee n

tannin, and antioxidant. The oil cake contains a high amount of nitro-
gen (8.34 percent). Regarding the biochemical evaluation from the oil
cake, it is evident that about 60 percent NaCl extractable protein is
digestible, which can be converted into biofertilizer or other useful
fodder. The extractable high quality of tannin present in fruit pulp is
used in the leather industry and in herbal medicines. The maximum
tannin was extracted at 135°C over 12 h with shaking. The seed coat
contains a high amount of gallic acid (3.2 mg/mL), which showed
good antioxidant properties in different vegetable oils.

13.3 Refining Edible Oil
The refining process is generally associated with the removal of trace
metals and various organic impurities known to be detrimental to oil
flavor and stability. Production costs depend on the amount of oil lost
in the process of removeing these impurities from the oil and the cost
of operating and maintaining the equipment used in the refining
process. A refinery running at 0.6 percent adsorbent with a produc-
tion rate of 1000 tons/day with 28 percent oil retention would have
an annual oil loss of 613 tons. The main object of each stage is to
obtain the best oil quality at the lowest cost.
Two schemes are generally employed: physical refining and
chemical refining. Physical processes are generally preferred over
chemical techniques.
Physical Refining The oil is heated to about 260°C to coagulate albu-
minoidal matter, which absorbs with it self much of the coloring mat-
ter. When cooled, the albuminoidal matter settles down. The clear oil
can be decanted off from the top or by filtration. Sometimes, physical
refining is done by distillation, which is steam stripping the oil at an
elevated temperature under reduced pressure. A new degumming
protocol has been developed that employs electrolyte solutions to
remove nonhydratable gums from soybean, rice bran, and mustard
oils. This protocol removes nonhydratable gums, mostly phospha-
tidic acid (PA) and phosphatidyl ethanolamine (PE), which is left
over after water degumming and cannot be removed without using
phosphoric acid or citric acid. Acid degumming is associated with
oil loss (~10 percent) due to its emulsifying nature and subsequent
washings. 9
Chemical Refining Chemical refining is done to remove the free fatty
acids and leave a neutral fat. The oil is churned with a solution of
caustic alkali to form soap with a free fatty acid. The soap settles
down along with the break and coloring matter. The clear oil is drawn
off, washed with water to remove the excess alkali, dried, and fil-
tered. This process results in a very pale-colored oil. Sometimes
sodium carbonate is used to remove the free fatty acids. Alternative