Fed-batch synthesis of galacto-oligosaccharides with Aspergillus oryzae β-galactosidase using optimal control strategy

Fed-batch synthesis of galacto-oligosaccharides (GOS) from lactose with β-galactosidase from Aspergillus oryzae was evaluated experimentally and reaction yield was maximized via optimal control technique. The optimal lactose and enzyme feed flow rate profiles were determined using a model for GOS synthesis previously reported by the authors. Experimentally it was found that fed-batch synthesis allowed an increase on the maximum total GOS concentration from 115 (batch synthesis) to 218 g L^-1 as consequence of the increase in total sugars concentration from 40 to 58% w/w. Such high concentration of total sugars was not attainable in batch operation because of the low solubility of lactose at the reaction temperature (40°C). Simulations predicted a GOS yield of 32.5 g g^-1 in fed-batch synthesis under optimal conditions, while experimentally the same yield as in batch synthesis was obtained (28 g g^-1). Besides, an enrichment of total oligosaccharides in GOS with a high polymerization degree (GOS-5 and GOS-6) was observed in the fed-batch synthesis. Experimental profiles for all sugars were similar to the ones predicted by simulation, which supports the use of this methodology for the optimization of GOS synthesis.