Saponification value (SV) or saponification number (SN) is a measure of the average molecular weight (or chain length) of all the fatty acids present in a sample of fat or oil in the form of triglycerides. It represents the number of milligrams of potassium hydroxide (KOH) or sodium hydroxide (NaOH) required to saponify one gram of fat under specified conditions. The smaller the average length of fatty acids, the lower the mean molecular weight of triglycerides, and vice versa, the higher the saponification value.
To determine the saponification value, the sample is treated with an excess of alkali (usually an ethanolic solution of potassium hydroxide) for half an hour under reflux. The KOH is consumed by reaction with triglycerides, which consume three equivalents of base. Diglycerides consume two equivalents of KOH.
Fats or oils with high saponification values (such as coconut and palm oil) are more suitable for soap making. The saponification value is also used to compute the number of acids (esters and free acids) in a fat or oil. The more saponification, the more short- and medium-chain fatty acids are present in the fat.
Other related values used in the analysis of fats and oils include:
- Hydroxyl value – Mass of KOH needed to neutralize 1 gram of acetylated substance
- Iodine value – Mass of iodine absorbed by 100 grams of a given substance
- Peroxide value – Measure of peroxide content of a fat or oil
- Soapmaking – Small scale process of producing soap
The saponification value is determined using the following formula: $$\text{Saponification value (mg/g)} = \frac{\text{mass of KOH used}}{\text{mass of sample}}$$
In summary, saponification value is a measure of the average molecular weight of all the fatty acids present in a sample of fat or oil in the form of triglycerides. It is determined by treating the sample with an excess of alkali and is used to compute the number of acids in a fat or oil. Fats or oils with high saponification values are more suitable for soap making.
