Enzymatic synthesis of fatty acid ascorbyl esters

Abstract

Lipase B from the yeast Candida antartica was used to catalyze the enzymatic synthesis of fatty acid ascorbyl esters, in 2-methyl-2-butanol as a solvent. The influence of water activity ( a w) and reaction medium hydrophobicity on the synthesis of 6- O-palmitoyl l-ascorbic acid were investigated through a transesterification reaction involving l-ascorbic acid and palmitic acid methyl ester as substrates. The catalytic activity of the enzyme and the production at equilibrium were affected by the pre-fixed a w, best results being obtained for the lowest a w values. The activation of the lipase was promoted by an increase in the methyl palmitate/ascorbic acid molar ratio ( R) up to 9, leading to 19 g/l of ascorbyl ester after a 5 h reaction time. That performance was not reached in a reaction medium of equal log P level, where methyl palmitate was partly substituted by a hydrophobic solvent. Results were applied to the syntheses of polyunsaturated fatty acid ascorbyl esters such as ascorbyl eicosapentaenoate, leading to a production range from 11 to 15 g/l, after a 3 h reaction time.