Enzymatic synthesis of fatty acid ascorbyl esters

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 Do-fixed a(w), best results being obtained far the lowest a, 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, when 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. (C) 1998 Elsevier Science B.V. All rights reserved.