Synthesis of propyl-β-D-galactoside with free and immobilized β-galactosidase from Aspergillus oryzae

Synthesis of propyl-β-galactoside catalyzed by Aspergillus oryzae β-galactosidase in soluble form was optimized using response surface methodology (RSM). Temperature and 1-propanol concentration were selected as explanatory variables; yield and productivity were chosen as response variables. Optimal reaction conditions were determined by weighing the responses through a desirability function. Then, synthesis of propyl-β-galactoside was evaluated at the optimal condition previously determined, with immobilized β-galactosidase in glyoxyl-agarose and amino-glyoxyl-agarose, and with cross-linked aggregates (CLAGs). Yields of propyl-β-galactoside obtained with CLAGs, amino-glyoxyl-agarose and glyoxyl-agarose enzyme derivatives were 0.75, 0.81 and 0.87 mol/mol and volumetric productivities were 5.2, 5.6 and 5.9 mM/h, respectively, being significantly higher than the corresponding values obtained with the soluble enzyme: 0.47 mol/mol and 4.4 mM/h. As reaction yield was increased twofold with the glyoxyl-agarose derivative, this catalyst was chosen for evaluating the synthesis of propyl-β-galactoside in repeated batch operations. Then, after ten sequential batches, the efficiency of catalyst use was 115% higher than obtained with the free enzyme. Enzyme immobilization also favored product recovery, allowing catalyst reuse, and avoiding browning reactions. Propyl-β-galactoside was recovery by extraction in 90%v/v acetone with a purity higher than 99% and its synthesis was confirmed by mass spectrometry.