Analysis of lipids

ANALYTICALPARAMETERSFOROILSAND
FATS
The properties of oils and fats vary along with the
degree of unsaturation, average molecular weight
and also acidity from hydrolysis.
Anumber of parameters are used for their analysis
which are included under physical constants and
chemical constants.
Physical constants include viscosity, specific gravity,
refractive index, solidification point etc.
Following is a brief idea about some of the analytical
parameters grouped under chemical constants.

1. Iodine value,
2. Saponification value,
3. Hydroxyl value,
4. Acetyl value,
5. Unsaponifiable matter,
6. Acid value,
7. Peroxide value,
8. Kreistest (rancidity index),
9. Estervalue,
10. Reichert Messle Value &,
11. Polenski value.

Iodine value
Definition: Iodine value is the number, which express in
grams, a quantity of halogen, calculated as iodine which is
absorbed by 100g of the substance under the described
condition.
Iodine value may be determined by iodine
monochloride method, iodine monobromide method,
pyridine monobromide etc.

Significance:
• Iodine value is the measure of unsaturation ( number
of double bond ) in fat.
• Iodine number is useful to analyze the degree of
adulteration
• On basis of iodine value the oils can be differentiated
into non-drying oil and semidrying oil.
Drying oil shows less iodine value, non-drying oil
shows more iodine value and semidrying oil shows moderate
iodine value.

Procedure:
•Iodine Monochloride Method: place an accurately
weighed quantity of substance being examined(castor oil) in
a dry 250ml capacity iodine flask.
• Add 1ml of carbon tetrachloride and dissolve in 20ml of
iodine monochloride solution. Insert the stopper and allow
to stand in the dark at a temperature in between 15-25
degrees Celsius for 30 mins.

• Place 15ml of potassium iodide solution and cup top,
carefully remove the stopper, rinse the stopper and sides
of the flask with 10ml of water, shake and titrate with
0.1M sodium thiosulphate using starch as an indicator.
• The starch solution added towards the end of the
titration. Note the ml required (a).
• Repeat the operation omitting the substance being
examined and note the number of ml required (b).
calculate the iodide value with the following expression.
Iodine value = [1.269(b-a)]/w
W – Weight in grams of the substance of the oil.

Saponification value is defined as the number of
milligrams of KOH required to neutralize the fatty acids
resulting from complete hydrolysis of 1 gm of the sample of
oil or fat.
Significance:Saponification value of fat or oil is one of
it’s characteristic physical properties.
• Saponification value occurs in an inverse proportion to
the average molecular weight of fatty acid present in oil.
• Higher saponification number for fats containing
short chain fatty acids.
Saponification value

• This value is normally applied for butter fat, coconut
oil in which lower fatty acids glycerides occur in high
content.
• It is used for detecting adulteration
• Saponification value is determined by refluxing a
known amount of sample with excess of standard alcoholic
KOH

Procedure:
•2 gm of the given sample of oil is accurately weighed
in a RB flask and refluxed with 25ml of 0.5M ethanolic
potassium hydroxide with a little pumic powder in a
water bath for 30 minutes.
•Add 1ml of phenolphthalein solution and titrate
immediately with 0.5M hydrochloric acid (a ml)
•Carry out the blank, omitting the substance under
examination (b ml)

•Calculate the saponification value
•Saponification value = 28.05 (b- a)/w
•b – volume of hydrochloric acid consumed in blank titration
•a – volume of hydrochloric acid consumed in sample
titration
•w – weight of the sample

Acid value is defined as the number of milligrams of
potassium hydroxide required to neutralize the free fatty
acids present in 1gm of sample of fat or oil.
Significance:
Acid value is used as an indication of rancid state.
Generally rancidity causes free fatty acids, which have
been liberated by hydrolysis of glycerides due to the action
of moisture, temperature or enzyme lipase.
Acid value

Acid value can be determined by treating sample with
solution of KOH using phenolphthalein as indicator
PROCEDURE
•Accurately weigh about 1gm of the oil and to this add 50
ml mixture of equal volume of ethanol (95%) and ether,
previously neutralized with 0.1M of KOH to phenolphthalein
solution.
•Add 0.1 ml of phenolphthalein solution and titrate with
0.1M KOH until the solution remains faintly pink

•n – number of milligrams of potassium hydroxide required
•w- weight of the sample.
•The STD for edible fats and oils indicate that the acid
value must not exceed 0.6
. The acid value can be determined by the formulae;
Acid value = 5.61

3. HYDROXYLVALUE:
It is defined as number of milligrams of potassium hydroxide
required to neutralize the acetic acid capable of combining
by acetylation with 1 g sample of fat or oil.
4. ACETYLVALUE:
It is the number of milligrams of potassium hydroxide
required to neutralize acetic acid obtained when 1g of sample
acetylated oil is saponified.

Significance
Acetyl number is a measure of number of
hydroxyl groups present.
to detect adulteration and rancidity.

5. UNSAPONIFIABLEMATTER:
It is the matter present in fats and oil, which after
saponification by caustic alkali and subsequent
extraction with an organic solvent, remains non-volatile
on drying at 8o°C.
It includes sterols (phytosterol and cholesterol), oil
soluble vitamins, hydrocarbons and higher alcohols.
Paraffin hydrocarbons can be detected by this method as
adulterants.

7. PEROXIDEVALUE:
PEROXIDE VALUE Is the number which expresses in milli
equivalents of active oxygen that expresses the amount
of peroxide containing 1000gms (kg) of substances
(meq/kg).
It is a measure of peroxides present in oil.
Aperoxide value is generally less than 10 mEqkg in
fresh samples of oil.
Due to temperature or storage, rancidity occurs
causing increase in peroxide values.

8. KREISTEST(RANCIDITYINDEX):
Due to rancidity, epihydrin aldehyde or malonaldehyde are
increased which are detected by Kreis test using
phloroglucinol which produces red colour with the
oxidized fat

9.ESTERVALUE:
It is defined as number of milligrams of potassium
hydroxide required to combine with fatty acids which
are present in glyceride form in 1 g sampleof oil or fat.
Difference between saponification value and acid
value is ester value.

10. REICHERTMESSLEVALUE:
This value is a measure of volatile water soluble acid
contents the fat.
It is defined as number of milli litres N/10 potassium
hydroxide solution required to neutralize the volatile
water soluble fatty acids obtained by 5 g fat.
Significance:
Higher content of volatile fatty acids of butter
responsible for its higher reichert-meissl number.
It is useful in testing purity/adulteration of butter.

11.POLENSKI VALUE:
It is defined as the number of millitres of N/10
potassium hydroxide solution required to neutralize
water-insoluble, steam - distillable acids liberated by
hydrolysis of 5 gm of fat.
Significance:
The Polenski value is an indicator of how much
volatile fatty acid can be extracted from fat through
safonification.

Analysis of lipids

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Analysis of lipids

Similar to Analysis of lipids (20)

Recently uploaded

Recently uploaded (20)

Analysis of lipids