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Table 1 Levels and codes of variables used for CCD

From: Carboxymethyl cellulase production optimization from newly isolated thermophilic Bacillus subtilis K-18 for saccharification using response surface methodology

Parameter Code Levels
−2 −1 0 +1 +2
Substrate conc. (%) X1 0.5 1.0 1.5 2.0 2.5
Inoculum size (%) X2 1 2 3 4 5
Yeast extract (%) X3 0.2 0.6 0.8 1.0 1.2
pH X4 4.5 5 5.5 6 6.5