Fig. 5
The 3D response surfaces and 2D contour plots for CRM A production in Medium N2. The effect of two variables on CRM A production is presented in each figure, while the other variable is held at zero level. a, b The effects of soluble starch (X1) and yeast extract (X2); c, d The effects of soluble starch (X1) and (NH4)2SO4 (X5); e, f The effects of yeast extract (X2) and (NH4)2SO4 (X5)