Table 1. Factors and levels of the response surface methodology

Factors Levels
High (-1) Medium (0) Low (+1)
Methanol concentration (%) 60 80 100
Temperature (°C) 25 55 85
Final equation in coded factors for response variables (Y)
  Luteolin TPC TFC ABTS DPPH
β0 +149.87 +1,249.52 +879.01 +45.30 +63.20
A +34.80 +420.10 +418.60 +19.29 +18.12
B +6.41 -69.80 -158.03 -5.53 -5.18
AB +0.2517 -35.53 -66.07 -4.08 -2.94
A2 -4.65 +43.10 +240.85 +7.10 +0.4602
B2 -36.47 -224.75 -279.69 -9.83 -12.89
Where: β0 is intercept, A is temperature, B is methanol concentration.