Optimization procedure: In this study, both multiple graphical
and numerical optimization procedures were applied to determine
the optimum different hot-air drying conditions on the
physicochemical properties of dried kaffir lime leaves. For
graphical optimization procedure, the final reduced models were
expressed as three-dimensional (3D) response surface plot to
better visualize the interaction effect of main drying conditions
on the physicochemical properties of dried kaffir lime leaves. The
3D plots were drawn by keeping one variable constant at the
center point and varying the other two variables within the
experimental range in order to show how each response variable
related to two continuous design variables. For numerical multiple