RESEARCH ARTICLE


System Development from Organic Solvents to Ionic Liquids for Synthesiz-ing Ascorbyl Esters with Conjugated Linoleic Acids



Zhiyong Yang1, Lise Schultz2, Zheng Guo1, Charlotte Jacobsen2, Xuebing Xu1, *
1 Department of Engineering, Aarhus University, DK-8000 Aarhus C, Denmark
2 National Food Institute, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark


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© 2012 Yang et al.

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: (https://creativecommons.org/licenses/by/4.0/legalcode). This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

* Address correspondence to this author at Department of Engineering, Aarhus University, Gustav Wieds Vej 10C, DK-8000 Aarhus C, Denmark; Tel: +45 89425089; Fax: +45 86123178; E-mail: xu@mb.au.dk


Abstract

The aim of this paper is to screen suitable reaction systems for the modification of antioxidants through enzy-matic synthesis. Enzymatic esterification of ascorbic acid with conjugated linoleic acid (CLA) was investigated as a mod-el. Four organic solvents and five different enzymes were evaluated. Results show that only Novozym® 435 turned out to be a useful enzymatic preparation for the production of ascorbyl-CLA ester. The optimum reaction conditions in the or-ganic solvent system were 4 h at 55°C and at a molar ratio of 5 (CLA/ascorbic acid). The esterification reaction was trans-ferred to an ionic liquid system for the purpose of improving solubility of the polar substrate and avoiding the application of organic solvents. From screening experiments, it was evident that only methyltrioctylammonium triflouroacetate (tO-MA·TFA) could provide a proper reaction environment for production of ascorbyl-CLA ester when using Novozym® 435 as biocatalyst. It was possible to significantly increase the productivity (150 g/l) through the increase of ascorbic acid sol-ubility in ionic liquids by super saturation together with the increase of reaction temperature to 70°C, far beyond than that in organic solvents (35 g/l) after preliminary optimizations for both systems.

Keywords: Ascorbic acid, CLA, Organic solvents, Ionic liquids, Esterification.