Enzymatic synthesis of conjugated linoleoyl ascorbate in acetone

Abstract

Conjugated linoleoyl ascorbates were synthesized through the condensation of cis-9, trans-11-conjugated linoleic acid ( c9, t11CLA) or trans-10, cis-12-conjugated linoleic acid ( t10, c12CLA) with l-ascorbic acid (AsA) using immobilized lipase in a water-soluble organic solvent at 50 °C. The conversion was higher at higher polarity of the solvent and a higher ratio of CLA to AsA. The conversion for the synthesis of t10, c12CLA-AsA was higher than those for c9, t11CLA-AsA and linoleoyl ascorbate (LA-AsA), when Chirazyme ® L-2 C2 from Candida antarctica type B, which has been commonly used for enzymatic reaction in organic solvent, was used as a catalyst. The unmodified CLA isomers were almost completely oxidized within 4 h at 65 °C and 75% relative humidity, whereas all the CLA-AsAs were significantly resistant to oxidation. The oxidation kinetics was empirically expressed by the Weibull equation, and the rate constant, k, was estimated. The k values for CLA-AsAs and LA-AsA were about 1/30 and 1/60, respectively, of that for the corresponding unmodified CLA isomers. The enzymatic modification of CLA with AsA was an effective technique for improvement in the oxidative stability of CLA.