Determination of Degree of Esterification of Agave sisalana Pectin by Diffuse Reflectance Fourier Transform Infrared Spectroscopy with Wavelet Transform

A rapid and sensitive method was developed for the determination of the degree of esterification(DE) of Agave sisalana pectin(ASP) by diffuse reflectance Fourier transform infrared spectrotroscopy(DRIFTS).By processing the pectin spectrum obtained by DRIFTS with wavelet transform,the distortion of the original spectral signal caused by light scattering was effectively eliminated,for example,the signal-to-noise ratio(SNR) increased from 84 to 96,while the signal-to-baseline ratio(SBR) increased from 7.7 to 8.3.The precision(expressed as RMSE)of the wavelet transform for ten replicates of ASP-h was 0.011 62.The pectin spectra showed that the intensities of the absorption peak and peak area(KM) of the esterified group at 1 740 cm-1 and the carboxyl group at 1 630 cm-1 were closely related with the DE.A linear relationship existed between DE and KM1740/(KM1740+KM1630) with a correlation coefficient of 0.988.For three pectin samples extracted from Agave sisalana with different technologies,the DE obtained for ASP-w,ASP-h and ASP-u by DRIFTS were 72.09%,62.98% and 35.31%,respectively.The results of Student t-test indicated that no significant difference existed between the results obtained by acid-base titration and DRIFTS methods.