Table 5. Comparison of Experimental and Predicted Values Using the Box-Behnken Design for the Four Independent Variables on the Content of Polyphenol from Aqueous NaOH Extraction.

	extraction temperature (°C)	extraction time (min)	solvent composition (%)	liquid–solid ratio	experimental value (%)	predicted value (%)
test N	T	t	C	V	content	eq 3
1	80	45	0.05	20	20	19.73
2	80	45	1.50	20	28	27.01
3	80	45	0.50	20	28	25.10
4	60	60	0.10	25	27	27.01
5	80	90	0.50	20	28	22.19
6	80	45	0.50	20	23	27.32
7	90	60	0.10	25	26	24.85
8	90	60	1.00	15	27	23.56
9	80	45	0.50	10	26	24.75
10	90	30	0.10	25	18	27.21
11	60	60	0.10	15	27	24.85
12	60	60	1.00	15	30	27.32
13	100	45	0.50	20	27	24.75
14	60	30	1.00	25	21	23.56
15	80	15	0.50	20	23	23.56
16	90	30	1.00	25	24	24.55
17	90	30	0.10	15	25	23.56
18	60	60	1.00	25	19	23.56
19	90	30	1.00	15	28	27.21
20	80	45	0.50	30	25	23.56
21	40	45	0.50	20	28	25.34
22	80	45	0.50	20	25	24.55
23	60	30	0.10	15	33	32.81
24	60	30	0.10	25	15	19.73
25	60	30	1.00	15	22	24.12
26	90	60	0.10	15	25	22.19
27	90	60	1.00	25	18	20.01
28	80	45	0.50	20	20	22.03