On optimization of enzymatic processes: Temperature effects on activity and long-term deactivation kinetics

Abstract

Enzymatic processes are industrially important. Process duration, temperature, and pH are critical factors to optimize. Longer processes can improve economics by requiring less enzyme. Both temperature and pH affect enzymes, but temperature has far stronger interactive effects with process duration, which has scarcely been considered. To fill this technology gap, we investigated both short- and long-term temperature effects on Aspergillus niger carbohydrases. For short-term effects, enzyme activities were measured at different temperatures and regressed with a model that considered catalytic activation-energy and protein-folding. The model-determined short-term optima were: α-galactosidase, 57.6 °C; sucrase, 53.4 °C; pectinase, 49.4 °C; xylanase, 50.4 °C; and cellulase, 46.5 °C. Long-term effects were evaluated at 40, 52, 55, 60, and 65 °C for 72 h to determine the activity decay constants and activation energies. The observed order of stability was sucrase > α-galactosidase > pectinase > xylanase, while cellulase showed more complex decay kinetics. These models enabled prediction of cumulative enzymatic performance at different temperatures and durations. The prediction for α-galactosidase was verified with experimental results of soybean molasses hydrolysis, giving 51% higher stachyose conversion after 72 h at 54 °C (predicted optimum) than 60 °C. The models developed and approach taken are valuable for optimizing enzymatic processes, which improve sustainability and environmental friendliness.