EXPERIMENT 3: DETERMINATION OF PHYSICOCHEMICAL PROPERTIES OF FATS/OILS.
A. Determination of Melting Point
By using a piece of
filter paper, fat or oil
that has been melted
was inserted 1 cm
length into a capillary
tube.
At temperature of
<0oC, the capillary tube
was cooled for 2 hours.
The tube was
submerged and
ensured that the top
end of the fat or oil
was 1 cm below the
level of water.
Approximate of 800 mL
of water was used in a
100 mL of beaker.
In the middle of the
beaker, a thermometer
was hang. The water
was then being heated
at the rate of 1oC/min.
As the fat starts to slip
out, the temperature
was recorded as well as
the temperature when
all the fat has slipped
out of the tube. The
temperature or the
range of temperatures
was referred as the slip
point or known as
melting point.
B. Determination of Refractive Index (RI)
The temperature used for the determination of RI using a refractometer and a sodium vapour lamp was
20oC for oils, 40-60oC for hydrogenated fats and 80oC for waxes.
For scale adjustment procedure, by
using a syringe, 2 to 3 drops of
distilled water were placed on the
main prism surface. The secondary
prism was then covered and
through the eyepiece, it was
observed.
The measurement knob was slowly
turned until the boundary line can be
observed in the view while looking
through the eyepiece. Hence, the
measurement knob was turned until
the view changed from dark to light. By
using the “high-low” switch on the
thermometer box, the degree of
lightness can be changed.
The colour of the boundary line was
removed by turning the colour
compensator knob. A clear boundary
line was then can be seen.
The refractometer was set at 1.3330
(Brix 0%), when the temperature
scale was 20oC. An adjustment was
carried out according to the chart in
the refractometer manual when the
temperature is other than 20oC.
The secondary prism was opened
and 2 to 3 drops of oils or fat at 40oC
was placed at the center of the main
prism. The sample was ensured to
be distributed evenly and no air
bubble. The secondary prism was
then closed with caution.
The boundary line with the crossed
line was coincided by turning the
measurement knob.
The RI was recorded.
C. Determination of Specific Gravity (SG)
An empty SG bottle was
weighed.
The SG bottle was filled with oil
or melted fat. The bottle was
closed with a stopper that has
a capillary bore.
The SG bottle was warmed at
25oC or room temperature
until the expansion has ceased.
The bottle was then being
cooled at 7oC for 24 hours.
The bottle was then wiped and
cleaned on the outside and
being weighed.
The SG of the oils or fats was
calculated.
D. Determination of Iodine Value
Product
Hydrogenated palm kernel oil, olein, stearin
Palm kernel oil, olein, stearin
Special high IV olein
Liquid oil, soya bean oil, etc.
Expected Iodine Value
<5
5 – 25
25 – 60
> 100
Sample Weight (g)
3.00
1.00
0.40
0.15
The sample was accurately weighted to
the nearest 0.0001 g into a dry and clean
reagent bottle or conical flask. The
weight of the sample used was varied
according to its expected iodine value.
The table above was used as guide.
Cyclohexane of 20 mL was added for
the fat or oils to be dissolved. The flask
was slightly warmed to facilitate
dissolution of fat or oil when
necessary.
The flask or bottle was placed in the
dark for 1 hour. For high IV oils which
are >150, a longer period of 2 hours
was required.
Wij’s solution of approximate 25 mL
was added and the stopper was
inserted before it was gently shaken.
Potassium iodide solution of 15% of 20
mL and 100 mL of distilled water after
standing.
Sodium thiosulphate solution of 0.1 M
was titrated until the yellow colour
due to iodine has almost disappear.
The flask was ensured to be well
shaken.
On the same test sample,
determinations were carried out.
Starch indicator solution of 1 m was
added and the titration was continued
until the blue colour disappears after a
very vigorous shaking.
2
Under the same conditions, a blank
test simultaneously being carried out.