Table 5.

Variables and levels of the central composite experimental design.

Independent Variables	Level
	Low (−1)	Medium (0)	High (1)
X1: solid/solvent ratio (g/mL)	1:10	1:20	1:30
X2: ethanol/water ratio (v/v)	25/75	50/50	75/25
Responses Variables	Goal
Y1: TPC (mg GAE/g sample dw)	Maximize
Y2: DPPH (mg Trolox/g sample dw)
Y3: FRAP (mg FeSO4/g sample dw)
Y4: ORAC (µmol Trolox/g sample dw)

TPC: total phenolic content; DPPH radical scavenging activity; FRAP: ferric reducing antioxidant power; ORAC: oxygen radical absorbance capacity; GAE: gallic acid equivalents; dw: dry weight.