Study of lipase-catalysed synthesis of ascorbyl benzoate in cyclohexanone using response surface methodology

BACKGROUND: Compared with ascorbic acid, ascorbyl esters exhibit many advantages. Their biosynthesis in organic media has been widely studied owing to its many advantages over chemosynthesis. However, since the natural substrates of lipase are fatty acid triacylglycerols, few data are available on the lipase-catalysed esterification of ascorbic acid with aromatic acids. Furthermore, although many reports can be found on the biosynthesis of ascorbic acid with fatty acids, few deal with the interactions between important reaction factors. The aim of the present study was to optimise the biosynthesis process of ascorbic acid with an aromatic acid, benzoic acid, in cyclohexanone using a statistical approach and to investigate the interactions among variables. RESULTS: Among the five factors studied, only substrate concentration, water activity and temperature had a significant effect on the reaction. Enzyme concentration affected the process slightly, while the effect of reaction time became minor after equilibrium. For the first time, using a partial derivative method, it was quantitatively demonstrated how the optimum of the variable studied depended on the constant values of fixed variables used in a single-factor experiment. Statistical analysis predicted a maximal conversion rate (47.66%) at enzyme concentration 10 g L-1, substrate concentration 0.1031mol L-1, water activity 0.4896, reaction time 48h and temperature 66.63 degrees C. CONCLUSION: This study illustrated possible factor interactions during the lipase-catalysed synthesis of ascorbyl benzoate in cyclohexanone, and a maximal conversion rate was achieved under optimal reaction conditions. (c) 2007 Society of Chemical Industry.