The effects of the different variables on the pectin yield and the
uronic acid content were then assessed by response surface
methodology (RSM) using the central composite design (CCD)
(Teófilo & Ferreira, 2006). CCD was built using the same variables as
in the fractional factorial design, but excluding the variable pH
because it lacked significance. Thus, the pH of citric acid employed
in CCD extractions was kept constant (pH 3) and the dependent
variables (responses) were pectin yield and uronic acid content of
the extracted pectin.