Quantitation of fat
There are certain chemical parameters used for the characterization of fats:
Acid value (or “neutralization number” or “acid number”) is the number of milligram of potassium hydroxide (KOH) that is required to neutralize one gram of fat. Thus, acid number is an indication of the quantity of free fatty acid present in the fat. The fat which has been processed and stored properly has a very low acid number.
The saponification number is the milligrams of KOH required to saponify 1 g of fat. Thus it provides the information about the average chain length of the fatty acids in the fat. The saponification number varies inversely with the chain length of the fatty acid.The shorter the average chain length of the fatty acid, the higher is the saponification number.
Iodine number is expressed as the number of grams of iodine absorbed by 100 g of fat. Not only iodine, but other halogens will also bind at double bonds. Hence bromine is often used instead of iodine because it is more reactive. The iodine number is a measure of the degree of unsaturation of the fatty acid in the fat.
Eg: the iodine numbers of linseed oil (PUFA), olive oil (MUFA), and coconut oil (saturated fatty acid) are approximately 175–201, 77–91, and 8–9.5, respectively.
The Polenske value indicates the level of volatile fatty acid in the fat. It is equal to the number of milliliters of 0.1N alkali (KOH) solution necessary to neutralize the water insoluble fatty acids. The value is named after the chemist who developed it, Eduard Polenske.
The Reichert value (Reichert-Meissl-Wollny number) measures the quantity of short chain fatty acid in the fat molecule. It is the number of milliliters of 0.1 N KOH solution necessary to neutralize the soluble, volatile fatty acids derived from 5 g of fat. The value is named after the chemists who developed it, Emil Reichert and EmerichMeissl.
Acetyl number is the measure of the free hydroxyl groups in a substance (as a fat or oil). It is the number of milligrams of potassium hydroxide required for neutralization of the acetic acid formed by the saponification of 1gm of fat after it has been acetylated.