Table 1.

Factors and levels of single factor design

Factor	Level/type
Glucose concentration (g/L)	25, 50, 100, 150, 200 and 250
Yeast concentration (g/L)	0, 2, 4, 6, 8 and 10
L-Phe concentraion (g/L)	0, 5, 10, 15, 20, 25 and 30
pH	1, 2, 3, 4, 5, 6, 7 and nature pH (4.98)
Temperature (oC)	20, 22, 24, 26, 28, 30 and 32
Shaking speed (rpm)	90, 120, 150, 180, 210, 240 and 270
Loading volume (mL/250 mL)	25, 50, 75, 100 and 125
Inoculum size (%, v/v)	0.1, 0.2, 0.4, 0.8, 1.6, 3.2, 6.4 and 12.8
Time point of L-Phe addition (h)	0, 12, 24, 36, 48 and 60
Time (h)	0, 12, 24, 36, 48, 60 and 72
Surfactant types	Control, glycerol, Tween-20, Tween-40, Tween-60, Tween-80, Triton X-100 and Triton X-114
Tween-60 concentration (g/L)	0, 2, 4, 8, 16, 32, 64 and 128