Fig. (3) Contour plots for temperature versus stirring speed in the hibiscus calyces extraction for TMA (Y₂) (A), where the variable X₁ was fixed in 0.5; and for ABTS (Y₃) (B), where the variables X₁ and X₄ were fixed in 0.5 (X₁: enzyme concentration; X₂: temperature; X₃: stirring speed; X₄: time).