Quantification of blockiness in pectins—A comparative study using vibrational spectroscopy and chemometrics |
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Authors: | Hanne Winning Nanna Viereck Jan Larsen |
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Affiliation: | a Quality and Technology, Department of Food Science, Faculty of Life Sciences, University of Copenhagen, Rolighedsvej 30, 1958 Frederiksberg C, Denmark b CP Kelco, Ved Banen 16, 4623 Lille Skensved, Denmark |
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Abstract: | The gelling properties of pectins are related not only to the degree of esterification (DE), but also to the distribution of the ester groups. In this study, we have examined an experimentally designed series of 31 pectins originating from the same mother pectin and de-esterified using combinations of two different enzymatic mechanisms. The potential of using infrared (IR), Raman, and near infrared (NIR) spectroscopies combined with chemometrics for reliable and rapid determination of the DE and distribution patterns of methyl ester groups in a designed set of pectin powders was investigated. Quantitative calibration models using partial least squares (PLS) regression were developed and compared. The calibration models for prediction of DE obtained on extended inverse signal correction (EISC)-treated spectra of all three spectroscopic methods yielded models with cross-validated prediction errors (RMSECV) between 1.1%p and 1.6%p DE and correlation coefficients of 0.99. A calibration model predicting degree of random de-esterification (R) and block de-esterification (B) was developed for each spectroscopic method, yielding RMSECV values between 4.4 and 6.7 and correlation coefficients (r) between 0.79 and 0.92. Variable selection using interval PLS (iPLS) significantly improved the prediction of R for IR spectroscopy, yielding RMSECV of 3.5 and correlation coefficients of 0.95. All three spectroscopic methods were able to distinguish the spectral patterns of pectins with different enzyme treatments in simple classification models by principal component analysis (PCA). Extended canonical variate analysis revealed one specific signal in the Raman (1045 cm−1) spectrum and one significant area (1250-1400 cm−1) in the IR spectrum which are able to classify the pectin samples according to the four different enzyme treatments. In both Raman and IR spectra, the signal intensity decreased in the sequence R-B > B > B-R > R > re-methylated pectin. |
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Keywords: | GalA, galacturonic acid HGA, homogalacturonan DE, degree of esterification DP, degree of polymerization RG-I, rhamnogalacturonan-I Rhap, ramnopyranosyl unit PME, pectin methyl esterase B, block de-esterification R, random de-esterification IR, infrared NIR, near infrared FT, Fourier transformed PC, principal component LV, latent variables PCA, principal component analysis CV, cross-validation RMSECV, root mean square of cross-validation PLS, partial least square iPLS, interval partial least square ECVA, extended canonical variates analysis EISC, extended inverted signal correction r, correlation coefficient %p, percent points |
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