Green synthesis of β-sitostanol esters catalyzed by the versatile lipase/sterol esterase from Ophiostoma piceae

Abstract

β-sitostanol esters, used as dietary complement for decreasing cholesterol absorption, have been synthesized at 28°C via direct esterification or transesterification catalyzed by the versatile lipase/sterol esterase from the ascomycete fungus O. piceae. Direct esterification was conducted in biphasic isooctane: water systems containing 10mM β-sitostanol and lauric or oleic acid as acyl donors, reaching 90% esterification in 3h with the recombinant enzyme. The use of molar excesses of the free fatty acids did not improve direct esterification rate, and the enzyme did not convert one of the two fatty acids preferentially when both were simultaneously available. On the other hand, solvent-free transesterification was an extremely efficient mechanism to synthesize β-sitostanyl oleate, yielding virtually full conversion of up to 80mM β-sitostanol in 2h. This process may represent a promising green alternative to the current chemical synthesis of these esters of unquestionable nutraceutical value.

Keywords: Enzymatic esterification; Lauric acid (PubChem CID: 3893); Lipase; Oleic acid (PubChem CID: 445639); Phytosterols; Sitostanyl ester; Solvent-free transesterification; Sterol esterase; β-sitosterol (PubChem CID: 222284).