Triglycerides

Why do triglycerides with longer fatty acids have a lower saponification number than those with shorter one?

Why do triglycerides with longer fatty acids have a lower saponification number than those with shorter fatty acids?

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1. The saponification number indicates the fatty acid chain length of a triglyceride. In order for saponification to occur, you need a certain ml of KOH to complete the hydrolysis of one gram of fat or oil. So basically, the value is just a measurement of the ml of KOH. Triglycerides with long fatty acids have more mass. As the mass increases, the saponification number decreases (an inverse relationship). So a given mass of a triglyceride will have a larger number of moles at low molecular weight than high, and accordingly consume a larger number of moles KOH.
2. Triglycerides are composed of three fatty acids linked to glycerol by fatty acyl esters (-O-CO-R). The fatty acids may be saturated (no C=C double bonds) or unsaturated. Liquid triglycerides are oils, while solid triglycerides are fats. Saponification: By heating a triglyceride in aqueous potassium hydroxide (KOH) the fatty acyl esters can be cleaved off (hydrolysis) leaving behind glycerol and the potassium salt of the fatty acid. The process is called “saponification” (or soap formation) since the potassium salts of fatty acids are in fact “soaps”. The “saponification number” is used as an indicator of fatty acid chain length in triglycerides. The value is simply a measurement of the ml of KOH required to complete the hydrolysis of one gram of fat or oil. Triglycerides containing long fatty acids will have a lower saponification number than triglycerides with shorter fatty acids -SINCE 1 GRAM OF LIPID CONTAINING LONG CHAINS WILL HAVE LESS CHAINS IN TOTAL THAN 1 GRAM OF LIPID CONTAINING SHORT CHAINS. Saponification value (or "saponification number", also referred to as "sap" in short) represents the number of milligrams of potassium hydroxide or sodium hydroxide required to saponify 1g of fat under the conditions specified. It is a measure of the average molecular weight (or chain length) of all the fatty acids present. As most of the mass of a fat/triester is in the 3 fatty acids, it allows for comparison of the average fatty acid chain length http://xnet.rrc.mb.ca/davidb/new_page_18.htm http://en.wikipedia.org/wiki/Saponification_number