Interesterification of butter fat by commercial microbial lipases in organic solvent media

The interesterification yield (IY) and changes in fatty acid positional distribution of selected butter fat triacylglycerols were investigated, using a wide range of commercial microbial lipases and organic solvent media. The interesterification of butter fat by lipase from Mucor miehei was carried out in hexane, hexane-chloroform, and hexane-ethyl acetate; the results showed that the addition of 30% of either chloroform or ethyl acetate to the hexane resulted in a 23% increase in the IY. The interesterification of butter fat in a microemulsion co-surfactant system, containing Brij 35 as surfactant and 1-heptanol as co-surfactant, resulted in an increase in the triacylglycerols that contain C18:0 at sn-2 position, located originally at sn-1,3 positions, with a concomitant interchange with C14:0 and C18:1 at the same position. The interesterification of butter fat by lipase from Rhizopus niveus, in a phosphatidylcholine reverse micellar system, showed an increase in C16:0 at the sn-2 position, with a concomitant decrease in the proportion of small chain fatty acids (C4-C10:0); however, the interesterification of butter fat in co-surfactant free microemulsion systems, containing hexane and ionic (phosphatidylcholine) and non-ionic (sorbitol monostearate and polyoxyethylene sorbitan monostearate) surfactants, showed that the interesterified selected triacylglycerols were enriched with C18:0 and C18:1, originally located on sn-1,3 position, at sn-2 position with concomitant interchange with C12:0, C14:0 and C16:0, originally located at the same position. The interesterification of butter fats, in co-surfactant free microemulsion system, by four microbial lipases showed that those catalyzed by lipase from R. niveus demonstrated a 46% increase in the proportion of C18:1 at sn-2 position whereas those catalyzed by enzymes from M. javanicus, R. delemar and M. miehei were enriched with C16:0 at the same position, by 21%, 35% and 41%, respectively. In addition, lipase from R. niveus was purified until homogeneity by ammonium sulfate fractionation followed by successive ion-exchange and size-exclusion liquid chromatographies. The purified enzyme fraction showed an optimum pH of 7.7 and a K{dollar}sb{lcub}m{rcub}{dollar} value of 0.29 mg/ml. The electrophoretic analyses of the purified fraction demonstrated the presence of a single band with a molecular mass of 26 {dollar}pm{dollar} 3 kD. Stereospecific analyses of selected butter fat triacylglycerols, interesterified by the purified lipase fraction, showed a 51% increase in the proportion of hypocholesterolemic fatty acids (C18:0 and C18:1) at sn-2 position, with a concomitant 40% decrease in that of hypercholesterolemic fatty acids (C12:0, C14:0 and C16:0), located at the same position.