Fig. 4From: Tofu processing wastewater as a low-cost substrate for high activity nattokinase production using Bacillus subtilisEffects of initial pH (a), shaking speed (b), liquid medium volume (c), and temperature (d) on nattokinase activity. a Control: pH 7, b Control: shaking speed 200 rpm, c Control: liquid medium volume 100 mL/500 mL, d Control: temperature 33 °C. *Significance code: P < 0.05; **Significance code: P < 0.01Back to article page