Table 1: Natural variables and factor levels. Coded variables: = (T-50): 20; = (pH-5.8): 0.8; = ( -8): 4.

Natural variablesFactor levels
−1.682−10+1+1.682

Temperature (T) (°C)16.430507083.6
pH4.4555.86.67.15
Time ( ) (h)1.3481214.7