Page 409 - Biosystems Engineering

386 Cha pte r T h i r tee n

Peroxide Value Method A 250-mL standard joint round-bottom flask
containing 100 g of oil was placed over a thermostatic bath. Air from
2
an air cylinder (pressure of the cylinder 1.7 kg/cm ) was passed
through the oil (2 mL/min). At different intervals oil was withdrawn
to determine peroxide values (PV) as follows. Weigh 0.1 to 0.2 g of oil
in a 250-mL iodine flask and add 15 cc of chloroform or carbon tetra-
chloride to dissolve it. Along with this, carry out a blank experiment.
Add 25 cc of Wij’s solution (7.9 gm of pure iodine trichloride in
100 mL of glacial acetic acid in a beaker by warming on a water bath.
In another flask containing dissolve 8.7 gm of iodine in a second
portion of warm 100 cc glacial acetic acid. Mix the two solutions in a
1000-mL measuring flask and fill the solution to the mark with glacial
acetic acid. Store the Wij’s solution in a freezer) to the flasks contain-
ing the fat and the blank. Allow the flasks to sit in the dark for about
30 min after adding 25 mL of a 10 percent solution of potassium iodide
to the neck of the flask. Then dilute the mixture with 50 to 60 mL of
water. Titrate it immediately against a 0.1-N sodium thiosulphate
solution. Shake vigorously and titrate again until the yellow color
almost disappears. Add a starch solution and titrate again until the
blue color disappears.
Let V and V be the number of cubic centimeters of N/10 sodium
b w
thiosulphate required for W g of fat. The amount of thiosulphate that
is the equivalent of iodine that reacts with W g of fat is calculated
using the following formula:

(V − V )×10 −3
b w
10 × W

From this, we get the amount of iodine in grams that react with W g
of fat:

(V − V )×10 −3
b w ×127
10 × W
where 127 is the equivalent weight of the iodine.
Therefore, the peroxide value (meqv of O /kg of lipid) and the
2
formula is meqv O /kg: [V (mL of thiosulphate) × N (thiosulphate)]
2
× 1000/W (g of fat sample):
(V − V )×10 −3 ×127 (V − V )×127
.
b w ×100 = b w
10 × W W
Thiobarbituric Acid Test The thiobarbituric acid (TBA) test was based

on the color reaction of TBA with malondialdehyde (mg/kg) in the
sample.