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Table 2 Regression analysis on the regression coefficient of polynomial models that explaine the influences of substrate concentration (X1) and treatment time (X2) on the yield and recovery of ferulic acid and NFPC from (a) pineapple peel (PP) and (b) pineapple crown leaves (PCL)

From: Bioconversion of ferulic acid attained from pineapple peels and pineapple crown leaves into vanillic acid and vanillin by Aspergillus niger I-1472

(a) Pineapple peel (PP)
CoefficientFerulic acidNFPC
YieldRecoveryYieldRecovery
Coefficientap-valuebCoefficientap-valuebCoefficientap-valuebCoefficientap-valueb
Linear
 β1+ 184.170.01+ 0.720.27+ 0.86< 0.00− 7.99< 0.00
 β2− 115.910.06+ 0.370.55+ 0.130.13+ 1.650.02
Quadratic
 β11− 64.000.01− 0.350.13− 0.32< 0.00+ 1.160.09
 β22− 79.11< 0.00− 0.730.01+ 0.170.06+ 1.390.05
Cubic
 β111− 12.690.69− 0.640.14
 β222+ 126.470.01+ 0.380.34
Interaction
 β12− 127.35< 0.00− 1.42< 0.00− 0.210.08− 2.500.01
(b) Pineapple crown leaves (PCL)
CoefficientFerulic acidNFPC
YieldRecoveryYieldRecovery
Coefficientap-valuebCoefficientap-valuebCoefficientap-valuebCoefficientap-valueb
Linear 
 β1+ 65.28< 0.00− 0.700.07+ 0.98< 0.00− 6.23< 0.00
 β2+ 62.39< 0.00+ 1.92< 0.00+ 0.020.76+ 0.590.49
Quadratic 
 β11− 5.840.13− 0.440.01− 0.28< 0.00− 1.460.14
 β22+ 5.510.14+ 0.190.13− 0.070.23− 1.440.14
Cubic 
 β111+ 20.780.02+ 0.820.01
 β222− 37.55< 0.00− 1.07< 0.00
Interaction 
 β12− 31.82< 0.00− 0.93< 0.00− 0.040.57− 1.350.28
  1. Note: aCoefficient indicates the regression constant of the linear, quadratic, cubic and interaction terms in the polynomial equation that explain the relationship between substrate concentration (X1) and treatment time (X2) with the yield and recovery of ferulic acid (Y1, Y2) and NFPC (Y3, Y4)
  2. bp-value lower than 0.05 indicate that the effect of the term on the yield and recovery of ferulic acid and NFPC are significant at 95% confidence interval. p-value lower than 0.01 indicate that the effect of the term on the yield and recovery of ferulic acid and NFPC are significant at 99% confidence interval