Selective enzymatic synthesis of lower acylglycerols rich in polyunsaturated fatty acids

Selective elimination of saturated fatty acid (FA) residues from vegetable oils (sesame, borage, olive, and sunflower) produces lower acylglycerols rich in unsaturated and polyunsaturated FA residues. Novozym (R) 435 releases greater amounts of saturated FA residues than unsaturated residues relative to other biocatalysts. Highest selectivity is obtained for 50 wt-% Novozym (R) 435 with respect to the oil and [ethanol]/[FA] = 25. Under these conditions, 88-90% of saturated residues are released versus only 44-45% of unsaturated residues. Product acylglycerols have ratios of unsaturated to saturated residues of 21.5-23.0 relative to 5.22-4.73 for the precursor oils. Ethanolysis is faster with Novozym (R) 435. This biocatalyst is much less susceptible to inactivation by ethanol than other biocatalysts. However, in excess ethanol ([EtOH]/[FA] 4.5-25), the rate and conversion both increased when the ethanol concentration decreased. The best combination of conversion and selectivity is obtained with 50 wt-% Novozyme 435 and [ethanol]/[FA] = 4.5. Under these conditions, the product obtained in 1 h contains ca. 48% triacylglycerols, 24% diacylglycerols and 28% monoacylglycerols; the mol percentage of unsaturated FA residues is 12.3 times greater than that of saturated residues. The sn-2 position is essentially free of saturated FA residues. After use for ten reaction cycles, Novozym (R) 435 retains 80% of its initial activity.