Table 3.

Regression coefficient, standard error, and Student’s t-test results of response surface for total anthocyanin content and antioxidant activity

Parameter	Estimate	SE	t ratio	Prob. > |t|
Total anthocyanin content (TAC)
Intercept	37.79	0.19	200.01	< .0001*
Agitation speed	− 0.38	0.12	− 3.24	0.0229*
Sample to solvent ratio	0.74	0.12	6.35	0.0014*
Extraction time	2.04	0.12	17.65	< .0001*
Agitation speed * sample to solvent ratio	− 0.82	0.16	− 5.00	0.0041*
Sample to solvent ratio * extraction time	1.75	0.16	10.68	0.0001*
Agitation speed * extraction time	3.25	0.16	19.88	< .0001*
Agitation speed * agitation speed	− 1.97	0.17	− 11.57	< .0001*
(Sample to solvent ratio)2	− 4.17	0.17	− 24.49	< .0001*
Extraction time * extraction time	− 4.05	0.17	− 23.76	0.0229*
Antioxidant activity (AA)
Intercept	21.39	0.22	98.36	< .0001*
Agitation speed	− 0.54	0.13	− 4.07	0.0096*
Sample to solvent ratio	− 0.95	0.13	− 7.12	0.0008*
Extraction time	0.00	0.13	− 0.03	0.9786
Agitation speed * sample to solvent ratio	− 0.84	0.19	− 4.47	0.0066*
Sample to solvent ratio * extraction time	− 1.03	0.19	− 5.48	0.0028*
Agitation speed * extraction time	0.82	0.19	4.35	0.0073*
Agitation speed * agitation speed	− 3.39	0.20	− 17.28	< .0001*
(Sample to solvent ratio)2	− 2.82	0.20	− 14.39	< .0001*
Extraction time * extraction time	− 0.82	0.20	− 4.18	0.0086*

SE standard error

*Value statistically significant at P < 0.05