Table 2.

Regression coefficients and ANOVA for the extraction yield of caffeine (%)

Terms	Coefficients
Intercept	82.55
X1 (pressure)	8.47*
X2 (temperature)	2.64
X3 (extraction time)	25.22*
X4 (CO2 flow rate)	20.56*
X5 (modifier concentration)	6.16*
X1X1	− 5.63*
X2X2	0.24
X3X3	− 11.53*
X4X4	− 8.95*
X5X5	− 1.93
R2	0.9321

*Significant at p < 0.05