Phytosterols, which comprise plant sterols (unsaturated) and stanols (saturated), have been studied for the past few years for their use in the food and drug industries. Important applications include the use of their ester derivatives as additives in foods, or directly as a drug, to lower serum cholesterol levels by blocking cholesterol absorption in the body. Other studies have shown benefits of the consumption of phytosterols, especially beta-sitosterol, by improving symptoms of benign prostatic hyperplasia, arthritis and modulation of the immune system, among others.

Phytosterols have similar structure to cholesterol and, the only difference between a sterol and a stanol is the presence, in the former, of a double bond in C-5 of the perhydrocyclopentanophenanthrene nucleus. Transesterification of mixtures of sterols and stanols with different lipases have been reported elsewhere (1, 2, 3) but none of the lipases investigated had shown selectivity towards any component of the mixture. In this study, we present for the first time the selective transesterification of stanols (saturated phytosterols), in a mixture of phytosterols, using lipase QL from Alcaligenes sp. The reaction was carried out under vacuum in a solvent free medium, using an excess of fatty acid esters to solubilize the phytosterols.

1. Martínez I., Markovits Alejandro, Chamy R., Markovits Andrés. Lipase-catalyzed solvent-free transesterification of wood sterols. Appl. Biochem. Biotechnol. 2004, 112: 55-62.

2. Weber N., Weitkamp P., Mukherjee K. Fatty acid steryl, stanyl, and steroid esters by esterification and transesterification in vacuo using Candida rugosa lipase as catalyst. J. Agric. Food Chem. 2001, 49: 67-71.

3. Weber N., Weitkamp P., Mukherjee K. Steryl and stanyl esters of fatty acids by solvent-free esterification and transesterification in vacuo using lipases from Rhizomucor miehei, Candida antarctica, and Carica papaya. J. Agric. Food Chem. 2001, 49: 5210-5216.