Weigh 0.5g or
measure 0.5ml using pipette of the oil sample in a conical flask, add 3 drops
of phenolphthalein indicator and add 20ml of ethanol. Titrate with 0.1N of
NaOH.
Observation: a
pink coloration is observed.
From the
calculation using the following equation the acid value is gotten
(Tv ×N×56.1) ÷
wt of sample used.
Peroxide Value;
The
peroxide value is a measure of the peroxides contained in the oil. During
storage, peroxide formation is slow at first during an induction period which
may vary from a few weeks to several months. When interpreting quantitative
results, the particular oil or fat, the temperature, etc should be considered.
The peroxide value is usually determined volumetrically. These methods depend
on the reaction of potassium iodide in acid solution with the bound oxygen
followed by titration of the liberated iodine with sodium thiosulphate.
Chloroform is normally used as solvent.
Procedure
Measure
o.5g of the sample, add 25ml of acetic acid and chloroform in the ratio 2:1.
Add 1ml of 10% KI and shake vigorously. Cover and keep in the dark for 1min and
add 35ml of starch indicator.
Observation:
color changes to purple upon the addition of starch indicator. Titrate with
0.02N Na2S2O3. Observation: color changes to
white
(1000×
(Tv2-Tv1) N) ÷
Wt of sample used. All in mg/kg
Saponification
Value
The
saponification value of an oil or fat is defined as the number of miligram of
potassium hydroxide required to neutralize the fatty acids resulting from the
complete hydrolysis of 1g of the sample. The esters of the fatty acids of low molecular
weight require alkali for saponification, so that the saponification value is
inversely proportional to the mean if the molecular weight of the fatty acids
in the glycerides present. The saponification value is of the most use for
detecting the presence of coconut oil (SV 255), palm kernel oil (SV 247), and
the butter fat (SV 225), which contain a high proportion of the lower fatty
acids.
Procedure
Weigh
0.5g pipette 0.5ml of the oil sample into a conical flask, add 50ml of 0.5N
ethanolic KOH and reflux and allow cooling for 30minutes. Add 3 drops of
phenolphthalein indicator and titrate with 0.5N HCl.
Observation:
color changes from pink to colorless.
Then carry out
the calculation to determine the saponification value
(56.1×0.5× (Tv2-Tv1)) ÷ wt of samples used. All in
mg/KOH/g
PROXIMATE ANALYSIS
Proximate
analysis is an analysis that is carried out to determine the presence of some
vital nutrient contents in food materials and non-food materials. These
nutrients or food materials include:
·
Crude fiber
·
Moisture content
·
Ash content
·
Protein digestion
·
Fat content
·
Carbohydrate
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