A 2H NMR lineshape study of -CH3 group dynamics in pectin gels (original) (raw)
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Eur Biophys J Biophys Lett, 1998
A protocol for partial thermally-induced depolymerization of differently methoxylated pectin samples is described. The resulting macromolecules have been fully characterized with various complementary techniques, such as size exclusion chromatography (SEC), potentiometry, viscometry and 13 C NMR. Optimum conditions afford samples at 50-80% yield with weight-average molecular weights in the 4 to 20 kDa range. The major fraction of these polysaccharides adopts the random-coil conformation and such samples are suitable for 13 C NMR structural studies at room temperature. The methoxyl distributions of two apple pectin samples with a degree of esterification (DE) between 54 and 74% and a citrus pectin (DE, 72%) were shown to be random in nature, whereas that of a lightly methoxylated apple pectin (DE 39%) was partially blockwise. The carbon relaxation parameters of the depolymerized pectins attain asymptotic values for M W > 4 kDa. The M W values estimated from intrinsic viscosity data with the Mark-Houwink relationship reported for native pectins are in good agreement with those obtained by either endgroup analysis (NMR) or SEC. Thus, all the physicochemical data indicate that the secondary structure of the isolated chains of depolymerized pectin is closely related to that of the parent polymers. Finally, pectinmethylesterase activity towards the depolymerized pectins was similar to that of the untreated samples. Fig. 1 Schematic drawing of pectin (rhamnogalacturonan I) showing the smooth and hairy regions
Compositional heterogeneity in pectic polysaccharides: NMR studies and statistical analysis
Macromolecular Symposia, 1999
Pectins are a class of heterogeneous polysaccharides used in the food industry as a result of their ability to form gels. They are primarily composed of a (1ŕ4)‐α‐D‐galactopyranosyluronic acid backbone where the carboxylic acid group is methyl esterified at a level which depends on the source of the pectin and processing conditions used to isolate the material. Of considerable interest is the distribution of the free acid and methyl ester groups along this polymer chain. NMR spectroscopy, coupled with statistical analysis, is a powerful technique for the study of sequence distribution of monomers. Experimental conditions (temperature, pD) are reported which are appropriate for the analysis of pectic polysaccharides. Results are presented from a study of sequence distribution in native, modified, and fractionated pectins using 1H and 13C solution NMR methods. The triad sequence information was examined using Bernoullian and Markovian probability models in conjunction with continuous ...
Quantification of the degree of blockiness in pectins using 1H NMR spectroscopy and chemometrics
Food Hydrocolloids, 2007
The gelling properties of pectins are known not only to be closely related 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 pectins originating from the same mother pectin and deesterified using combinations of two different enzymatic mechanisms. The DE and distribution patterns of methyl ester groups have been analyzed using high-resolution (HR) 1 H nuclear magnetic resonance (NMR) spectroscopy on pectin solutions. Quantitative calibration models using partial least squares (PLS) regression were developed with the ability to predict DE as well as the specific enzyme treatment, expressed as amount of ester groups removed with random and block enzyme, respectively. NMR spectroscopy was able to distinguish between enzyme treatments in simple classification by principal component analysis (PCA). This was due to the spatial structure of pectin together with the methyl ester distribution. Nuclear Overhauser effect spectroscopy (NOESY) experiments confirmed all the general assignments with the expected nuclear Overhauser effect (NOE) correlations. Degree of random deesterification (R) was better predicted than the degree of block deesterification (B). The calibration models for prediction of R obtained on extended inverted signal correction (EISC) processed data gave a root mean square error (RMSE) of cross-validation (CV) of 2%p with 4 PLS components (latent variables, LV) and a correlation coefficient (r) of 0.98. Spectral variable selection using interval PLS (iPLS) was shown to be valuable, as all the calibration models were improved. r
Process–Structure–Function Relations of Pectin in Food
Critical Reviews in Food Science and Nutrition, 2015
Pectin, a complex polysaccharide rich in galacturonic acid, has been identified as a critical structural component of plant cell walls. The functionality of this intricate macromolecule in fruit-and vegetable-based derived products and ingredients is strongly determined by the nanostructure of its most abundant polymer, homogalacturonan. During food processing, pectic homogalacturonan is susceptible to various enzymatic as well as non-enzymatic conversion reactions modifying its structural and, hence, its functional properties. Consequently, a profound understanding of the various process-structure-function relations of pectin aids food scientists to tailor the functional properties of plant-based derived products and ingredients. This review describes the current knowledge on process-structure-function relations of pectin in foods with special focus on pectin's functionality with regard to textural attributes of solid plant-based foods and rheological properties of particulated fruit-and vegetable-derived products. In this context, both pectin research performed via traditional, ex situ physicochemical analyses of fractionated walls and isolated polymers and pectin investigation through in situ pectin localisation are considered.
External and internal gelation of pectin solutions: microscopic dynamics versus macroscopic rheology
Journal of physics. Condensed matter : an Institute of Physics journal, 2014
Pectin is a natural biopolymer that forms, in the presence of divalent cations, ionic-bound gels typifying a large class of biological gels stabilized by non-covalent cross-links. We investigate and compare the kinetics of formation and aging of pectin gels obtained either through external gelation via perfusion of free Ca(2+) ions, or by internal gelation due to the supply of the same ions from the dissolution of CaCO3 nanoparticles. The microscopic dynamics obtained with photon correlation imaging, a novel optical technique that allows obtaining the microscopic dynamics of the sample while retaining the spatial resolution of imaging techniques, is contrasted with macroscopic rheological measurements at constant strain. Pectin gelation is found to display peculiar two-stage kinetics, highlighted by non-monotonic growth in time of both microscopic correlations and gel mechanical strength. These results are compared to those found for alginate, another biopolymer extensively used in ...
Carbohydrate Research, 1999
Variable temperature and magnetic field dependent 13 C NMR relaxation measurements (T 1 , T 2 , and NOE) were carried out on a series of linear homopolysaccharides: a-(1 3)-D-glucan, b-(13)-D-glucan in Me 2 SO-d 6 , and a-(1 6)-D-glucan in D 2 O and Me 2 SO-d 6 dilute solutions. The relaxation data of the backbone carbons were analyzed quantitatively by using a variety of theoretical unimodal and bimodal time-correlation functions in an attempt to describe the main carbohydrate chain dynamics as a function of linkage position and stereochemistry. Among these, the time-correlation function developed by Dejean, Laupretre, and Monnerie (DLM) offered the best quantitative description of the segmental motion of the carbohydrate chains. The internal rotation of the hydroxymethyl groups about the exocyclic C-5 -C-6 bonds superimposed on segmental motion has been described as a diffusion process of restricted amplitude. Comparison of the dynamics of polysaccharides has been extended to include amylose and inulin studied previously. On the basis of the calculated correlation times for segmental motion, the flexibility of the carbohydrate chains decreases from inulin and dextran following the order; inulin\ dextran\a-(1 3)-D-glucan\ b-(1 3)-D-glucan amylose, whereas the rate and the amplitude of the internal rotation of the hydroxymethyl groups about the exocyclic C-5 -C-6 bonds showed that the restriction of the hydroxymethyl internal rotation decreases from inulin to amylose following the order; inulin\ a-(1 3)-D-glucan b-(1 3)-D-glucan\ amylose. Solvent effects on segmental dynamics and the temperature-frequency superposition of the relaxation data of the three polysaccharides have been discussed as well.
Magnetic Resonance in Chemistry, 2018
As interaction between proteins and polysaccharides is expected to change the average diffusion coefficient and the distribution width, it is believed that NMR diffusometry can be a useful tool to study and quantify the interaction between whey protein isolate (WPI) and low methoxyl pectin (LMP). For this purpose, the influence of pH, dry‐heat‐treatment duration, and WPI to LMP ratio on WPI and LMP interaction was evaluated using pulsed field gradient NMR. At pH 5.0 and 5.5, approximately 40–50% of the WPI present in the mixture interacted with LMP through electrostatic interaction. Hence, it is important to measure the degree of covalent interaction at a pH where electrostatic interaction between WPI and LMP is limited. The diffusion coefficient of WPI gradually decreased as the mixtures of WPI and LMP were incubated for 1, 2, 8, and 16 days, which was accompanied by an increase in the distribution width. With regard to the LMP concentration, the higher the LMP concentration, the h...
Water mobility in acidified milk drinks studied by low-field 1H NMR
2007
Low-field nuclear magnetic resonance (LF-NMR) transverse relaxation (T 2 ) was used to characterise acidified milk drinks (AMDs) with varying composition. Pectin was added to the AMDs at concentrations of 0.0%, 0.1%, 0.3% or 0.5% and the protein used was either skim milk powder (SMP) or SMP with added whey protein concentrate. Distributed exponential analysis of the T 2 relaxation revealed that the AMDs contained a single water component and that the T 2 relaxation times and distributions differed significantly with respect to pectin concentration and protein type. Temperature profiles (5-25-5 1C) showed that pectin concentrations of 0.3% or 0.5% prevented phase separations in the AMDs as a consequence of heating and cooling, whereas a new free water component emerged in the samples with pectin concentrations of 0.0% or 0.1% pectin. Overall, LF-NMR provides a powerful tool for elucidating industrially relevant texture problems such as whey separation.
Carbohydrate Research, 2009
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 À1 ) spectrum and one significant area (1250-1400 cm À1 ) 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.