Table 1.

Real and coded values of the independent variables in the rotatable central composite design and observed results

Assay	Temperature (°C)	Ethanol (%)	Citric acid (%)	TPCa	MACb	ORACc	ABTS·+d
1	30 (− 1)	30 (− 1)	0.8 (− 1)	1387.2 ± 66.2	65.8 ± 1.8	142.5 ± 15.2	70.7 ± 1.2
2	30 (− 1)	30 (− 1)	3.2 (+ 1)	1606.9 ± 43.2	76.1 ± 5.9	120.9 ± 0.7	80.1 ± 1.7
3	30 (− 1)	70 (+ 1)	0.8 (− 1)	1873.6 ± 9.5	144.1 ± 2.6	236.0 ± 8.7	103.2 ± 2.4
4	30 (− 1)	70 (+ 1)	3.2 (+ 1)	2319.0 ± 43.2	150.61 ± 6.5	213.3 ± 5.2	98.6 ± 2.4
5	50 (+ 1)	30 (− 1)	0.8 (− 1)	2287.2 ± 50.1	88.2 ± 3.3	202.2 ± 7.3	103.2 ± 3.0
6	50 (+ 1)	30 (− 1)	3.2 (+ 1)	2382.6 ± 25.0	107.0 ± 6.6	200.2 ± 11.5	115.9 ± 3.2
7	50 (+ 1)	70 (+ 1)	0.8 (− 1)	2657.0 ± 68.8	163.2 ± 3.0	250.2 ± 6.1	136.0 ± 1.8
8	50 (+ 1)	70 (+ 1)	3.2 (+ 1)	2962.0 ± 103.4	161.2 ± 2.9	340.3 ± 9.9	140.0 ± 2.7
9	23 (− 1.68)	50 (0)	2 (0)	2378.8 ± 103.9	142.4 ± 7.2	267.4 ± 7.6	122.1 ± 2.0
10	57 (+ 1.68)	50 (0)	2 (0)	4038.9 ± 116.8	149.3 ± 9.0	285.5 ± 17.8	180.9 ± 1.2
11	40 (0)	16 (− 1.68)	2 (0)	951.8 ± 51.2	46.4 ± 0.8	129.1 ± 15.2	45.6 ± 1.5
12	40 (0)	84 (+ 1.68)	2 (0)	1510.8 ± 64.1	143.8 ± 0.7	204.2 ± 13.1	83.7 ± 3.6
13	40 (0)	50 (0)	0 (− 1.68)	2109.1 ± 71.9	158.4 ± 11.2	264.5 ± 14.3	136.5 ± 3.8
14	40 (0)	50 (0)	4 (+ 1.68)	2848.3 ± 30.9	154.2 ± 1.4	233.6 ± 9.3	137.9 ± 4.2
15	40 (0)	50 (0)	2 (0)	2638.0 ± 162.2	163.6 ± 4.4	261.4 ± 7.4	148.3 ± 6.4
16	40 (0)	50 (0)	2 (0)	2422.9 ± 139.2	164.5 ± 5.9	256.9 ± 9.6	152.7 ± 4.6
17	40 (0)	50 (0)	2 (0)	2513.5 ± 130.6	141.9 ± 10.7	271.8 ± 12.7	149.7 ± 3.3

Results expressed as mean ± standard deviation (n = 3)

^aTPC: total phenolic content (mg of gallic acid equivalents [GAE]·100 g⁻¹ skin flour)

^bMAC: monomeric anthocyanin content (mg of malvidin-3-O-glucoside [Mv3gl]·100 g⁻¹ skin flour)

^cORAC: oxygen radical absorbance capacity (µmol Trolox equivalents [TE]·g⁻¹ skin flour)

^dABTS^·+: cation radical scavenging activity (µmol Trolox equivalents [TE]. g⁻¹ skin flour)