Enzymatic synthesis of monoacylglycerol citrate optimized by response surface methodology

Abstract

The ability of immobilized lipase B from Candida antarctica (Novozym 435) to catalyze the direct esterification of citric acid (CA) and monoglyceride (MG) for citrate esters of monoacylglycerols (CITREM) preparation was investigated. The effects of substrate concentration, molecular-sieve amount, substrate molar ratio, reaction temperature, time, and enzyme load on the conversion of CA in the reaction were investigated. Enzyme screening and the effect of solvent on the esterification were also investigated. RSM was used to optimize the effects of the reaction temperature (45-55 C), the enzyme load (6-10%; relative to the weight of total substrates), and the reaction time (24―48 h) on the conversion of CA. Validation of the RSM model was verified by the good agreement between the experimental and the predicted values of CA conversion. The optimum preparation conditions were as follows: CA concentration 0.12 mol/L, molecular-sieve 120 g/L, molar ratio of MG/CA 2:1, temperature 54.18°C, enzyme load 9.0% (relative to the weight of total substrates), and reaction time 47.5 h. Under the suggested conditions, the conversion of CA was 77.4%. Repeated reaction tests indicated that Novozym 435 could be used eight times under the optimum conditions with 92% of its original catalytic activity still retained.