Butter fat indices indicate the type and amount of fatty acids in the butterfat of any given dairy product, which helps in scoring the quality of the product. Many methods, including the gerber method, exist for determining the butterfat content. However, the indices we shall be looking at not only reveal the content but also the type of fatty acids present in the butterfat sample.
The two common fat indices include:
It is a base catalyzed hydrolysis of an ester into its constituent elements of alcohol and acid.
Saponification number is the amount (in mg) of a base/alkali (KOH) that completely hydrolyzes one gram of fat.
The higher the saponification value, the higher the amount of short-chained volatile fatty acids present in the fat sample.Saponification value is the amount of an alkali needed to completely hydrolyze 1 g of fat. Click To Tweet
Stearin + Potassium hydroxide —> Potassium stearate + Water
If the fat contains low molecular weight fatty acids, the number of molecules in one-gram fat sample will be greater than of the fat of high molecular weight fatty acids. Thus, the fat with low molecular weight fatty acids will have a higher saponification number.
Fats with high saponification value are prone to hydrolytic rancidity.
CH3(CH2)16 + 3KOH —> 3KOOCC17H35 + C3H5(OH)3
This is the most important and widely used of the indices. It states the ideal value/percentage of the iodine (or any other hydrogen) required to bind a 100 g fat. As such, it is an addition reaction.
This is significant because, in fat with double bonds, iodine reacts readily with the fat’s double bonds to form an additional compound.Iodine value gives a picture of the degree of saturation of fatty acids present in a given fat. Click To Tweet
Iodine number, therefore, gives a picture of the degree of saturation of fatty acids present in a given fat. Research shows that oleic acid is the most predominant of the unsaturated fatty acids present in the milk fat.
Consequently, iodine value has been taken to indicate the measure of oleic acid content in milk, hence, the softness of the fat.
The normal level of iodine value in milk ranges between 24 to 46. It depends on the feeding regime of the animal. Certain fodder concentrates promote high iodine value, e.g. sunflower cakes make animals produce fat with high iodine number.
On the other hand, palm oil cake and coconut cakes, produces fats with low iodine value.