Use of cyclic anhydrides to remove cholesterol and other hydroxy compounds from fats and oils

A method for removing cholesterol from animal fats has been developed based on the reaction between the hydroxyl group of cholesterol and cyclic anhydrides. The reaction forms monoesters with acyl chains having a terminal free acid group. The conversion of cholesterol into an acid derivative makes it possible to remove the cholesterol from fats by extraction with aqueous alkali. A study of the reaction in model systems showed that optimal conditions were a molar ratio of cholesterol to succinic anhydride of 1∶3 at 135°C for several hours. Acid catalysts increased the rate of the reaction, and acetic was selected not only because of its catalytic power but also because its reflux prevented the distillation of the cyclic anhydride from the reaction mixture. If all the cyclic anhydride was added at the beginning of the reaction, animal fats such as lard, tallow and milk fats were reduced in their cholesterol content by about 40%. A study of the reaction mechanism showed that the cholesterol reduction could be increased to 60–70% by altering the amount and the addition sequence of cyclic anhydride. The effectiveness of acid catalysts was related inversely to the negative logarithm of their acid dissociation constant (pK), but as their effectiveness increased, so did their tendency to form other, unwanted esters of cholesterol. A mixture of monoethyl fumarate and acetic acid sped the reaction, compared with acetic acid alone, with minimal formation of cholesteryl acetate. Studies with 14 C‐cholesterol showed little formation of products other than cholesteryl hemiscuccinate during the reaction. The procedure removed some of the tocopherol from the fat but had no other detectable effect on fat stability. The procedure also can be used to concentrate the lactone precursors from milk fat.