Enzymatic fatty acid exchange in digalactosyldiacylglycerol

Six different lipases were screened for their ability of acidolysis between digalactosyldiacylglycerol (DGDG) and heptadecanoic acid in toluene. Lipas es from Geotrichum candidum, Alcaligenes sp. and Penicillium camembertii di d not catalyse the acidolysis reaction. Rhizopus arrhizus and Rhizomucor mi ehei (Lipozyme) catalysed the acidolysis but produced a mixture of DGMG, DG DG, acyl-DGMG and acyl-DGDG. The extra acyl group is bound to the primary h ydroxyl of the digalactosyl moiety. Candida antarctica also catalysed the a cidolysis but the TLC analysis showed bands with higher R-f values than acy l-DGDG, these probably being different tetra and higher esters. R. arrhizus lipase was the most promising enzyme under the conditions used, with no te tra esters being formed and giving the highest reaction rate of the enzymes investigated. Low water activity (0.06 err 0.11) and high fatty acid conce ntration (400 mM) increased the formation of acyl-DGDG whilst higher water activities (0.33 and 0.54) increased the amount of DGMG when R. arrhizus li pase was used as catalyst. At a water activity of 0.11 and a fatty acid con centration of 400 mM a yield of 24% modified DGDG was obtained. In this pro duct the fatty acid originally present in the sn-l position had been exchan ged by heptadecanoic acid. (C) 2000 Elsevier Science Ireland Ltd. All right s reserved.