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The significant factors (yeast extract, lactose and pH) and their combined effect were studied by RSM for optimisation of remazol golden yellow decolourisation using M. endophyticus ES37. As per CCD, the dye removal rate varied from 0.43 to 77.49% (Table 8). Second-order polynomial model Equation (6) and CCD results were linked in order to elucidate the dependence of the dye removal ratio by multiple regression analysis. The estimated regression coefficient for the model is given in Table 9. The magnitude of coefficient had high significance (P = 0) for all factors during the decolourisation process. In addition, the correlation coefficient (R2) was determined by regression analysis and was found to be 83.43%, thus a higher value of R2 indicated a good correlation between the factors and CCD dye decolourisation process.
formula
6
where Y is predicted dye decolourisation (%), and X1, X2 and X3 were the coded values of lactose, yeast extract and pH, respectively.
Table 8

CCD mediated decolourisation (%) with predicted values

Percentage decolourisation
TrialLactose (X1)Yeast extract (X2)pH (X3)ExperimentalPredictedResidual
0.1 0.1 22.09 6.12 15.96 
0.1 56.68 50.03 6.64 
0.1 31.55 21.54 10.00 
60.2 56.82 3.37 
0.1 0.1 27.76 30.10 −2.34 
0.1 51.21 60.18 −8.97 
0.1 40.2 45.81 −5.61 
52.33 67.26 −14.93 
−0.20 0.55 3.32 13.53 −10.21 
10 1.31 0.55 77.25 68.49 8.75 
11 0.55 −0.20 39.42 45.63 −6.21 
12 0.55 1.31 69.31 64.55 4.75 
13 0.55 0.55 3.64 0.43 21.33 −20.90 
14 0.55 0.55 10.36 69.74 50.28 19.45 
15 0.55 0.55 74.81 72.59 2.21 
16 0.55 0.55 77.49 72.59 4.89 
17 0.55 0.55 71.3 72.59 −1.29 
18 0.55 0.55 70.99 72.59 −1.60 
19 0.55 0.55 70.5 72.59 −2.09 
20 0.55 0.55 70.71 72.59 −1.88 
Percentage decolourisation
TrialLactose (X1)Yeast extract (X2)pH (X3)ExperimentalPredictedResidual
0.1 0.1 22.09 6.12 15.96 
0.1 56.68 50.03 6.64 
0.1 31.55 21.54 10.00 
60.2 56.82 3.37 
0.1 0.1 27.76 30.10 −2.34 
0.1 51.21 60.18 −8.97 
0.1 40.2 45.81 −5.61 
52.33 67.26 −14.93 
−0.20 0.55 3.32 13.53 −10.21 
10 1.31 0.55 77.25 68.49 8.75 
11 0.55 −0.20 39.42 45.63 −6.21 
12 0.55 1.31 69.31 64.55 4.75 
13 0.55 0.55 3.64 0.43 21.33 −20.90 
14 0.55 0.55 10.36 69.74 50.28 19.45 
15 0.55 0.55 74.81 72.59 2.21 
16 0.55 0.55 77.49 72.59 4.89 
17 0.55 0.55 71.3 72.59 −1.29 
18 0.55 0.55 70.99 72.59 −1.60 
19 0.55 0.55 70.5 72.59 −2.09 
20 0.55 0.55 70.71 72.59 −1.88 
Table 9

Estimated regression coefficients for CCD

S. no.VariableCoef.SE coef.TP
Constant 72.5917 5.548 13.085 0.000* 
Lactose 16.3401 3.681 4.439 0.001* 
Yeast extract 5.6242 3.681 1.528 0.158 
pH 8.6070 3.681 2.338 0.041* 
Lactose*Lactose −11.1646 3.583 −3.116 0.011* 
Yeast extract*Yeast extract −6.1866 3.583 −1.727 0.115 
pH*pH −13.0031 3.583 −3.629 0.005* 
Lactose*Yeast extract −2.1575 4.809 −0.449 0.663 
Lactose*pH −3.4575 4.809 −0.719 0.489 
10 Yeast extract*pH 0.0725 4.809 0.015 0.988 
S. no.VariableCoef.SE coef.TP
Constant 72.5917 5.548 13.085 0.000* 
Lactose 16.3401 3.681 4.439 0.001* 
Yeast extract 5.6242 3.681 1.528 0.158 
pH 8.6070 3.681 2.338 0.041* 
Lactose*Lactose −11.1646 3.583 −3.116 0.011* 
Yeast extract*Yeast extract −6.1866 3.583 −1.727 0.115 
pH*pH −13.0031 3.583 −3.629 0.005* 
Lactose*Yeast extract −2.1575 4.809 −0.449 0.663 
Lactose*pH −3.4575 4.809 −0.719 0.489 
10 Yeast extract*pH 0.0725 4.809 0.015 0.988 

*Significant.

R2 = 83.43% R2(adj) = 68.51%.

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