Substrate selectivity in esterification of less common fatty acids catalysed by lipases from different sources

Abstract

Lipases from microorganisms (Candida cylindracea, Rhizopus arrhizus and Rhizomucor miehei), animal tissue (porcine pancreas) and a higher plant (rape, Brassica napus) have been evaluated as biocatalysts in the esterifications with n-butanol with regard to their substrate specificity towards fatty acids having a cis-4 unsaturation, e.g. docosahexaenoic (n-3 22:6), cis-6 unsaturation, e.g. petroselinic (n-12-18:1), γ-linolenic (n-6 18:3) and stearidonic (n-3 18:4), as well as cis-8 unsaturation, e.g. dihomo-γ-linolenic (n-6 20:3) acid, and fatty acids having unusual structures, e.g.cyclopentenyl (hydnocarpic and chaulmoogric), hydroxy (ricinoleic and 12-hydroxystearic) and epoxy (cis- and trans-9,10-epoxystearic) acids. A common feature of all the lipases tested is their ability to discriminate strongly against unsaturated fatty acids having a cis-4, cis-6 or a cis-8 unsaturation as substrates for esterification, whereas cyclopentenyl, hydrocy and epoxy acids are very well accepted as substrates. Esterification of the fatty acids of Hydnocarpus wightiana seed oil with n-butanol, catalysed by each of the above lipases, revealed that, as compared to the cyclopentenyl fatty acids having saturated alkyl chains, gorlic acid — a cyclopentenyl acid having a cis-6 unsaturation — is also strongly discriminated against as a substrate for esterification.