2.8 Design of Experiment
For response surface design, the following table was the procedure for the experimental setup for central composite design. The design of experiment was adopted to study the responses which are percentage free fatty acid content and total vitamin E content of the hydrolysed sample. The independent variables that determined the experimental system were weight of water (\(H_{2}O)\), weight of lipase, and reaction time. Variables were coded at five levels: -\(\alpha\), -1, 0, 1, and\(\alpha\). The range of values that describe the magnitude of both actual and coded are shown in Table 2.1. In the central composite design, five start-points and six replicate runs were incorporated to provide for estimation of model curvature and allow for the estimation of pure error respectively Chu et al. (2003). All experiments within this setup were done in a random order to minimise the effect of unexplained variability in observed responses due to extrinsic factors. Statistical analyses for the optimization procedure was done using the Design Expert (Version 11) software. A quadratic polynomial was assumed for predicting the responses of the regression models.
Table 2.1 Experimental Protocol for Central Composite Design for enzymatic hydrolysis of palm fatty acid distillate