Table 1.

Factors and levels for response surface methodology, Box–Behnken design matrix (in coded and uncoded level of three variables), experimental data and predicted values for three-level-three-factor response surface analysis

Run	Variable levelsa			TAC (mg C3GE/100 g FW)		AA (mg AAE/g FW)
	x1	x2	x3	Observed	Predicted	Observed	Predicted
1	600(0)	0.5(− 1)	1(− 1)	30.26	30.05	19.29	19.52
2	400(− 1)	1.25(0)	1(− 1)	31.98	31.85	16.82	16.70
3	800(+ 1)	1.25(0)	1(− 1)	27.44	27.61	17.58	17.68
4	600(0)	1.25(0)	1(− 1)	24.84	25.01	16.19	15.99
5	400(− 1)	0.5(− 1)	8(0)	30.13	30.47	15.94	15.83
6	800(+ 1)	0.5(− 1)	8(0)	31.31	31.36	16.76	16.43
7	600(0)	1.25(0)	8(0)	37.72	37.79	21.75	21.39
8	600(0)	1.25(0)	8(0)	37.99	37.79	21.34	21.39
9	600(0)	1.25(0)	8(0)	37.66	37.79	21.08	21.39
10	400(− 1)	2(+ 1)	8(0)	33.62	33.58	15.29	15.62
11	800(+ 1)	2(+ 1)	8(0)	31.53	31.19	12.74	12.85
12	600(0)	0.5(− 1)	15(+ 1)	27.80	27.63	17.67	17.88
13	400(− 1)	1.25(0)	15(+ 1)	32.61	32.44	18.85	18.75
14	800(+ 1)	1.25(0)	15(+ 1)	35.06	35.19	15.48	15.60
15	600(0)	2(+ 1)	15(+ 1)	35.39	35.60	17.85	17.62

TAC total anthocyanin content, AA antioxidant activity

^ax₁, agitation speed (rpm); x₂, sample to solvent ratio (g/40 mL); x₃, extraction time (min)