Optimal UAE extraction conditions were determined by RSM
which was performed using the Design Expert Version 7.1.3 software
(Stat-Ease, Inc., Minneapolis, MN). A central composite design
(CCD) was used to investigate the effects of two independent variables
(ultrasonication amplitude and extraction time) on the
dependent variables (steroidal alkaloids content). The data obtained
from the CCD design was fitted with a second order polynomial
equation. The equation was as follows