2.4. Response surface methodology for optimisation of stevioside
extraction using various enzyme combinations
To explore the effects of independent variables on the response
within the range of investigation, a central composite design (CCD),
with the five factors, was conducted. These factors were, pectinase
concentration (A), cellulase concentration (B), hemicellulase concentration
(C), temperature (D) and incubation time (E). The variables,
and their levels for the central composite design, are
shown in Table 1. The independent variables and their ranges were
chosen, based on preliminary experiment results. A second-order
quadratic equation was then fitted to the data by multiple regression
procedure (Alam & Nadzir, 2008). For a five-factor system, the
model equation is: