Technical processes of chemical esterification presently used for the preparation of steryl esters are generally performed at high temperature in the presence of chemical catalyst, accompanying with high energy consumption, browning of products and low selectivity. This work reported a novel approach to synthesize phytosterol ( -sitosterol as a model) fatty acid esters by employing immobilized CAL A which shows a superior catalytic activity to other immobilized lipases including CAL B, Lipozyme NS-40044 TLL and Lipozyme TL IM. CAL A achieves 6-14 times faster esterification of -sitosterol with myristic acid than other lipases. The effects of enzyme concentration, fatty acid types, substrate molar ratio, reaction temperature and time, and polar/non-polar organic solvents were investigated. A series of -sitosteryl fatty acid esters (C2-C18) have been successfully prepared with structural identification of products by 1HNMR and Fourier transform-infrared spectroscopy (FTIR). CAL A showed low activity towards short chain fatty acids (C2-C6) but it increased significantly in the presence of fatty acid anhydride counterparts. CAL A rendered remarkably high activity for medium and long chain fatty acids (≥ C8). An increase in double bond in fatty acid molecule reduced the esterification activity of CAL A. Reaction time, temperature, enzyme load, substrate ratio and concentration, and solvent property are found to profoundly influence reaction rates. 93-98%Yield of -sitosteryl esters could be achieved with hexane as solvent, fatty acid (C8-C18)/-sitosterol (1:1, mol:mol), 5-10% CALA load at 40- 50°C for 24h. This work demonstrated the promising potential of CAL A in bioprocess of phytosterols for value-added application.
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104th AOCS 104th AOCS Annual Meeting & Expo, 2013