*2.6. Experimental Design*

The effect of process parameters in the enzymatic transesterification reaction and the optimum conditions for the selectivity and viscosity were studied using a multifactorial design of experiments with three factors run by the software StatGraphics®version XVI centurion; Statgraphics.Net, C/Bravo Murillo 350, 1º, 28020 Madrid, Spain. Two of the variables were studied at three levels and the other one at two levels (Table 1), giving us 36 runs. The experiments were performed in random order. The experimental parameters selected for this study were immobilized lipase amount, oil/ethanol molar ratio and NaOH 10N amount. Table 1 shows the coded and actual values of the process parameters used in the design matrix.


**Table 1.** Process parameters in factorial design: coded and actual values.

As can be seen in Table 1, the ranges studied are the following: weight of Lipozyme RM IM, from 0.01 to 0.03 g, oil/ethanol volume ratio between 12/2.9 to 12/3.5 mL/mL (equivalent to molar ratios from 1/4 to 1/6, approximately) and the amount of 10N NaOH between 25 and 50 μL. Each experiment is done in triplicate to ensure about the reproducibility of each reaction and improve the model.
