Enzymatic synthesis of prebiotic carbohydrates from lactose: Kinetics and optimization of transgalactosylation activity of β-galactosidase from Aspergillus oryzae

The aim of the study was to analyze galactooligosaccharide (GOS) synthesis catalyzed by β-galactosidase from Aspergillus oryzae by applying experimental data to optimization and kinetic parameter estimation methods. The apparent kinetic parameters were determined in varying initial lactose concentrations by using six-step, 11-parameter GOS synthesis mechanism. The results revealed that GOS yield was mainly dependent on initial lactose concentration; on the other hand, all of the reaction parameters affected the required time to achieve maximum GOS yield (TMGY) significantly. The values of 32 °Brix, 36.8°C, and 8.32 U/g lactose solution were determined as the optimum reaction experimental set which offers 26.73% GOS yield and 369.82 min TMGY. The increased enzyme-galactose complex dissociation ratio (k₃/k₋₃) with decreasing initial lactose concentration resulted to low GOS productivity although GOS production/GOS dissociation rate ratio (k₄/k₋₄) increased with decreasing initial lactose concentration. This result signified that hydrolysis characteristics dominated the reaction medium at low initial lactose concentration. The role of monosaccharide inhibition became important on GOS synthesis for increasing initial lactose concentration. Practical Applications: The proposed study deals with investigation of the effects of initial lactose concentration, enzyme concentration, and temperature on enzymatic synthesis of galactoligosaccharide (GOS) from lactose by β-galactosidase from Aspergillus oryzae (βgAO) and estimation of apparent kinetic rate constants of the reaction which is important to design of futuristic strategies improving the GOS yield. Low GOS yield is the main concern of the prebiotic food industry due to thermodynamic and kinetic realities of the reaction. Deeper evaluation of the reaction mechanism will contribute valuable data to the partners in the scope of designing more productive engineering methods.