PHAN (FINALS): Fats, Fixed oils andFatty substances

Constant

- value or number of physical and chemical property. Correctness of these values determines the

quality of substances judged.

• Specific Gravity

• Melting Point

• Congealing Point

• Refractive Index

• Optical Activity

SMORC

• Acid Value

• Saponification Value

• Ester Value

• Iodine Value

• Acetyl Value

• Hydroxyl Value

• Unsaponifiable Matter

• Water and Sediment

Examples of Constants: (5)

Chemical Values: 8

constants

Determining Purity of Fixed Oils, Fats, Waxes, and Resins:

• Usual methods like gravimetric or volumetric processes cannot determine their purity.

• Instead, we use _____ (like acid value, saponification value, etc.) to check purity.

color, odor, taste and special identity test

determination of these constants are made in conjunction with the study of ___, ____, ___ and ____ for the substance analyzed and for the presence of adulterants serve as a basis of the purity and quality of such

substances

Fats

- compounds consisting of fatty acids combined with glycerol via ester linkages.

Fixed oils and fats

are mixture of glyceryl esters

of high molecular weight fatty acids like palmitic (16), stearic (18) and oleic( 18) acids.

Fixed oils

contain relatively high quantities of liquid glycerides (glyceryl oleate)

Fats

contain large amounts of solid glycerides (glyceryl stearate)

Source from animals

Fats

Sources

Mainly animals

Oils

Sources

Mainly plants

Fats

Fatty acid

Saturated

Oils

Fatty acid

Unsaturated

Fats

Bonding

No double bond

Oils

Bonding

Have double bond

Fats

State at room conditions

Solid

Oils

State at room conditions

Liquid

Fats

Melting point

High

Oils

Melting point

Low

Waxes

are esters of high molecular weight monohydric alcohols and high molecular weight fatty acids

Both plants (soybean, carnauba) and animals (spermaceti head of whale, Ambergris intestine of sperm whale)

Wax

are low melting point solids and have long alcohols chain

are only saponified by alcoholic alkali.

fats and oils

are made from glycerol and three fatty acids joined by dehydration

synthesis

maybe saponified by means of either aqueous or alcoholic alkali

Balsams

are substances containing benzoic or cinnamic acids or esters of these

Aromatic resins

Used as incense

Resins

are natural or induced solid or semi-solid exudates from plants characterized by being insoluble in water,

soluble in alcohol and ether, crystallizable and softening or melting at a moderate heat.

• If turbid (cloudy due to stearin), heat at 50°C in a water bath to clear.

• If still not clear, filter through dry filter paper using a hot water jacket.

This ensures the sample is clean before testing its chemical constants.

Sample Preparation of Fats and Oils

- First, determine:

Specific Gravity

Melting Point

- Acid Value (Acid Number / Acidity Index):

- Measures the free acids in a substance.

Expressed as:

• mg of KOH needed to neutralize 1g of sample

or

• mL of 0.1N NaOH needed for 10g of sample

Analysis of Fats and Oils

Free acids

Acid Value:

are due to hydrolysis of the esters that compose them

hydrolysis

Acid Value:

is caused by the catalytic action of light and heat, by bacterial action and by chemical treatment.

High Acid Value

hydrolytic decomposition

If substance has a ____, it does not indicate rancidity but _____ during their preparation, purification or storage.

rancidity

Bacterial action on free acids

1. Dissolve 10.0 g of the sample in 50 mL of equal parts alcohol and ether.

2. If it doesn't dissolve cold, warm with a condenser and shake until dissolved.

3. Add 1 mL phenolphthalein.

4. Titrate with 0.1 N KOH or NaOH until the solution stays faintly pink for 30 seconds.

Acid Value Determination

Saponification Number or

Koettsdorfer Number

Saponification Value Also known as

Saponification Value

-Defined as the number of mg of potassium hydroxide required to neutralize the free acids and saponify the esters in 1 gram of fat, fatty oil, wax, resin, balsam or other substances of similar composition.

Saponification value

Determination of this constant helps in the detection of

the presence of glycerides of fatty acids which contain

less than 16 or more than 18 carbon atoms because the

saponification value is inversely proportional to the

average of the molecular weights of the fatty acids

found in the sample.

High SV

low MW

_____, samples contain ____fatty acids

Weigh 1.5 to 2 g of the cottonseed oil sample into a 250 mL flask.

Add 25 mL of 0.5 N alcoholic KOH.

Reflux on a water bath for 30 minutes, shaking frequently.

Add 1 mL phenolphthalein.

Titrate the excess alkali with 0.5 N HCl.

Perform a blank test (same steps without the oil).

Saponification Value of Cottonseed Oil

HCl

____ cannot be substituted with H2SO4 because K2SO4 which would be the product of the neutralization will not dissolve in the alcoholic solution and interfere with the observation of the

endpoint.

Alcoholic KOH

____ is more advantageous than the aqueous solution because the alcohol acts as a solvent for the oil and the products of saponification which are insoluble in water

blank test

is performed to eliminate errors from all sources like those produced by absorption of CO2 by the alkali or by

the alkalinity of the glass vessels

Ester Value

Defined as the number of mg of potassium hydroxide required to saponify the esters in 1 gram of fatty oil, fat, wax, balsam, resin or other similar substances

Substances, which do not contain free acids, have equal ester and saponification values.

Substances containing free acids have their ester values equal to the difference between the acid value and

saponification value

Ester Number

Ester Value also known as

ester value

is important in the analysis of beeswax, which serves to indicate the presence of adulterants like

paraffin.

is determined together with the acid value to detect adulterants like rosin, stearic acid, or their mixtures.

These substances raise the acid value and lower the ester value, indicating possible adulteration of the wax.

PARAFFIN wax

is consists of High MW

aliphatic hydrocarbons

Unsaponifiable Matter

are substances that are not saponified by alkali hydroxides but are soluble in ordinary fat solvents.

Determining this residue helps detect unsaponifiable adulterants like petroleum oil in products such as linseed oil.

Phytosterol

After saponification, a small residue remains:

- ____ if from vegetable origin

Cholesterol

After saponification, a small residue remains:

- ____ if from animal origin

Weigh ~5.0 g of oil or fat into a 250 mL conical flask.

Add 50 mL alcoholic KOH and reflux for 1 hour on a steam bath, swirling often.

Cool to below 25°C, then transfer to a separator, rinsing the flask with two 50 mL portions of water.

Extract with three 100 mL portions of ether.

Combine ether extracts in a second separator containing 40 mL water.

Let the layers separate and discard the lower aqueous layer.

Wash the ether layer:

Twice with 40 mL water

Once with 40 mL of 3% KOH

Once again with 40 mL water

Continue washing with 40 mL water until the final wash is neutral (no pink with phenolphthalein).

Transfer ether extract to a tared flask, rinse separator with 10 mL ether, and add rinsings to the flask.

Evaporate ether on a steam bath.

Add 6 mL acetone, then remove it with air.

Dry the residue at 105°C until the weight is constant (difference ≤1 mg).

Determination of Unsaponifiable Matter:

Iodine Value

Defined as the number of grams of iodine absorbed under specified condition by 100 grams of oil, fat, wax or other substance.

This value is a quantitative measure of the proportion of unsaturated fatty acids present both free and combined as esters that have the property of absorbing iodine.

The determination of iodine number is important since it indicates whether they are pure or a mixture.

Iodine Number

Iodine Value Also known as

1. Drying Oils (Iodine value: >120)

- Example: Linseed oil, Cod liver oil

2. Semi-drying Oils (Iodine value: 100-120)

- Example: Cottonseed oil, Sesame oil

3. Non-drying Oils (Iodine value: <100)

- Example: Olive oil, Almond oil

Types of fixed oils based on Iodine

value (3)

Just read

❖ The determination of iodine number not only serves to help in

the identification of known oils but also to indicate the class

to which an unknown fat or oil belongs.

❖ In conjunction with the saponification value of a fat or oil,

iodine value also serves as a means of detecting adulteration.

❖ There are several methods used for the determination of the

iodine number e.g. Hubl, Hanus and Wijs which are generally

designated by the name of their originators. The method

given in the USP is the latter.

Hanus method

Method I is ____- Iodobromide, CHCl3

Wijs method

Method II is _____ - Iodochloride, CCl4

Hydroxyl Value Or Hydroxyl Number

Defined as the number of milligrams of potassium hydroxide equivalent to the hydroxyl content of one gram of the substance.

This constant gives an indication of the identity and purity of fatty substances possessing alcoholic hydroxyl groups.

An abnormally low hydroxyl value is indicative of adulteration with higher molecular weight alcohols or with non-alcoholic fatty substances e.g.

paraffin and petroleum oil HV 1/α mol wt

Acetyl Value of Fatty Acids

Number of mg of KOH needed to neutralize acetic acid from 1 g of acetylated fatty acids.

Closely corresponds to hydroxyl value; both reflect identity and purity

Acetyl Value

Determined by acetylating hydroxy fatty acids (e.g. hydroxystearic acid, hydrogenated castor oil) and finding the saponification value of the acetylated sample.

❖ Then calculated using the saponification value of the acetylated fatty acid and the acid value of the original fatty acid.

Peroxide Value

- the number , in mEq of oxygen, of

peroxides in 1 gram sample

Anisidine Value

- Defined as 100 times the absorbance

(at 350nm) of a solution resulting from reaction of 1g of

fat in 100mL of solvent

Total oxidation Value

- combined PV and Anisidine value (2PV + AV)

Solidification Temperature of FA -

Congealing point

Fatty Acid Composition