Independent variables Level Coded values -1.414 -1 0 +1 +1.414 X1 = Volume of protein 2 mg/mL solution (µL) 880.6 980.0 1220.0 1460.0 1559.4 X2 = Volume of 6.1 N TCA solution (µL) 11.7 20 40 60 68.3 Dependent variables       Y1= Absorbance of the supernatant recorded at 280 nm Y2 = Percentage of protein precipitated (% w/w)

Table 1: Independent variables and their level in central composite design and dependent variables.

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