油中的皂化值

The test method for determining saponification value of fat and oil is stipulated in major standards as a quality control. “Saponification value” is the mg value of potassium hydroxide (KOH) required to completely saponify 1g of the sample. “Saponification” is a chemical reaction of hydrolysis of esters, the following formula shows the saponification of ethyl acetate as one of the most typical reactions. CH3COOC2H5 + NaOH 􀃆 CH3COONa + C2H5OH Fat and oil containing such as stearic acid and palmitic acid require a large amount of alkali to saponify. The saponification value is used as an indication to know molecular weight of fatty acid contained by measuring how much alkali is consumed for saponification. There are two methods to determine saponification value: one is acid/base titration based on color indicator titration and the other is potentiometric titration. This application note describes the saponification value determination by potentiometric titration. The sample is heated with ethanolic potassium hydroxide to saponify, and the residual potassium hydroxide is titrated with hydrochloric acid after cooling (back titration).