Liquid fermentation technology optimization of nattokinase: from Lab-scale to Pilot-scale.

Nattokinase is a high-valued functional component produced during natto fermentation, and both its activity level and production yield are of significant importance for industrial applications. This study aimed to optimize and scale up the fermentation process for nattokinase production. We first optimized the liquid fermentation process for nattokinase through single-factor and response surface methodology (RSM) experiments, determining the optimal medium composition. Under the optimized conditions, a nattokinase activity of 4257 IU/mL was attained in shake-flask fermentation. Subsequently, a fed-batch cultivation process was employed in pilot-scale experiments. In a 20 L fermenter, dynamic control of oxygen supply and optimization of feed addition timing were implemented, resulting in an increase of the nattokinase activity to 23,074 IU/mL. When scaling up to a 200 L fermenter, an innovative strategy was adopted to overcome the oxygen transfer efficiency bottleneck. This approach involved low-speed startup, stirring-dominated oxygen control, and strict ventilation restrictions. As a result, the nattokinase activity reached 21,312 IU/mL, equivalent to 92.36% of the activity achieved in the 20 L fermenter. This optimized and scalable process provides a stable and controllable technical solution for pilot-scale upscaling, and establishes a strong foundation for large-scale industrial production of nattokinase.