Effect of organic media and temperature on activity and stability of immobilised Candida antarctica lipase in carbohydrate fatty acid ester synthesis Peter Degn* Lars Haastrup
Pedersen *Corresponding author
The effect of solvents, solvent mixtures and temperature on an immobilised lipase from C. antarctica was investigated regarding catalysis of the conjugation of myristic acid and a range of mono- and oligosaccharides. The activity of 6-O-myristate-D-glucopyranose synthesis was increased approximately six-fold (from 3.7 to 20.2 µmol min-1 g-1) by changing the solvent from pure tert-butanol to a mixture of tert-butanol/pyridine (45:55 v/v), increasing the temperature from 45 to 60°C, and optimising the ratio between glucose, myristic acid and the enzyme preparation. Addition of more than 2% DMSO to the tert-butanol:pyridine system had a negative effect on the enzyme activity. Lowering the water content of the enzyme preparation from 0.85% (w/w) resulted in significant decreases in enzyme activity, whereas increasing the water content up to 2.17% (w/w) did not significantly affect the enzyme activity. Significant amounts of the initially unsolubilised glucose was converted into ester within 24 h of incubation. Myristic acid esters of fructose (22.3 µmol min-1 g-1), a-D-methyl-glucopyranoside (26.9 µmol min-1 g-1), b-D-methyl-glucopyranoside (13.8 µmol min-1 g-1), maltose (0.9 µmol min-1 g-1) could also be prepared using the tert-butanol/pyridine solvent system with initial activities higher than previously reported. No synthesis activity was observed with maltotriose, cellobiose, sucrose and lactose as substrate. While the activity of the enzyme increased by a factor 1.4 when the reaction temperature was increased from 45°C to 60°C, the residual activity after 24 h dropped considerably at temperatures above 53°C. |
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