Amidated pectins—characterization and enzymatic degradation

Blue-light emitting aminated pectin for detecting Cu2+ ion

This research studied the chemo-sensing of low-cost aminated pectin (PE) obtained by a facile calcination under ammonia gas at temperature no higher than 175 °C without excessive use of alkaline, acid or solvents. The ammonia gas was found to replace the hydroxyl and methoxyl group, enhancing the crystallinity and solubility of the resultant pectin than those calcined in air or in 5% H₂. Though the increase of light absorption could be attributed mainly to the dehydration during calcination which caused the formation of CC double bond or aromatic ring, the N incorporation could be important to the photoluminescence (PL) emission. The PL quenching of the blue fluorescent aminated pectin showed a good linearity with the concentration of Cu²⁺, Fe³⁺ and the highest sensitivity toward Cu²⁺ among the investigated metal ions. In order to further increase the PL quenching toward Cu²⁺ and decrease the interference of Fe³⁺, a method involving H₂O₂ and ultraviolet illumination was developed to catalyze the oxidation of fluorophores on the polymer. This work provides new horizon on the modification and application of pectin in chemosensing.

Pectin as a rheology modifier: Origin, structure, commercial production and rheology

Pectins are a diverse family of biopolymers with an anionic polysaccharide backbone of α-1,4-linked d-galacturonic acids in common. They have been widely used as emulsifiers, gelling agents, glazing agents, stabilizers, and/or thickeners in food, pharmaceutical, personal care and polymer products. Commercial pectin is classified as high methoxy pectin (HMP) with a degree of methylation (DM) >50% and low methoxy pectin (LMP) with a DM <50%. Amidated low methoxy pectins (ALMP) can be obtained through aminolysis of HMP. Gelation of HMP occurs by cross-linking through hydrogen bonds and hydrophobic forces between the methyl groups, assisted by a high co-solute concentration and low pH. In contrast, gelation of LMP occurs by the formation of ionic linkages via calcium bridges between two carboxyl groups from two different chains in close proximity, known as the 'egg-box' model. Pectin gels exhibit Newtonian behaviour at low shear rates and shear-thinning behaviour when the shear rate is increased. An overview of pectin from its origin to its physicochemical properties is presented in this review.

Complexation of amidated pectin with poly(itaconic acid) as a polycarboxylic polymer model compound

Complexes based on amidated pectin (AP) and poly(itaconic acid) (PIA) were prepared by casting films from solutions of AP and PIA in different ratios with the pectin amount ranging from 10% to 90% by mass. The complexes were investigated by elemental analysis, Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and thermogravimetry (TG). In all investigated ratios of AP/PIA glassy transparent films with a uniform structure were obtained. The results of elemental analysis confirmed the composition of the complexes, and FTIR spectroscopy has shown carboxylic and amide peak shifting, indicating complex formation between AP and PIA. Comparison of thermograms of AP/PIA films with different ratios of AP indicated that the increase of the amount of AP increases the thermal stability of the films by retarding the onset of the main degradation processes.

Chromatographic and Enzymatic Strategies To Reveal Differences between Amidated Pectins on a Molecular Level

The intermolecular distributions of amide groups within two commercial LMA pectins was studied after removal of the methyl esters followed by fractionation of the different populations by anion exchange chromatography. The populations obtained had almost equal degrees of amidation while the values of the degree of blockiness were not the same, indicating also a different intramolecular distribution of the substituents considered as semirandom. Populations from the methyl-esterified amidated pectins showed a rather random distribution for almost all populations. A striking difference between these different populations was that, despite the same level of substitution, the ratio between amide groups and methyl esters varied significantly, indicating a heterogeneous amidation process.

Degree of blockiness of amide groups as indicator for difference in physical behavior of amidated pectins

Thickening and gelling properties of commercial amidated pectins depend on the degree of amidation and methyl-esterification, but also the distribution of these groups is of great importance. Methods have been developed during the last few years to determine the distribution of methyl esters over the pectic backbone. We applied the strategies developed for the analysis of high methyl-esterified pectins for studying the distribution of amide groups in amidated pectins. Low methyl-esterified amidated (LMA) pectins were digested before and after removal of methyl esters by an endo-polygalacturonase to determine the degree of blockiness of the substituents. The nature of the substituents (amide groups compared to methyl esters) did not modify the behavior of the enzyme. Oligomers released were separated by using high-performance anion exchange chromatography and pulsed amperometric detection (HPAEC-PAD) at pH 5. Fractions collected after on-line desalting were identified by using MALDI-TOF mass spectrometry. Oligomers were found to elute from the column as a function of their total charge. For the same overall charge and size, oligomers with methyl esters eluted before oligomers with amide groups. Both amide groups and methyl esters of the LMA pectins studied were found to be semirandomly distributed over the pectic backbone, but this may vary according to the amidation process used.