Rapeseed hull pectin

A pectin isolated from rapeseed, hulls by extraction with aqueous ammonium oxalate, had a degree of esterification of 83% and contained residues of hexuronic (mainly D-galacturonic) acid (76%), D-galactose (2–3%), L-arabinose (8–9%), D-xylose (2%), L-rhamnose (2–3%), and L-fucose (1%). Partial acid hydrolysis of the derived pectic acid furnished 2-O-(α-D-galactopyranosyluronic acid)-L-rhamnose, 4-O-(α-D-galactopyranosyluronic acid)-D-galacturonic acid and the polymer-homologous tri- and tetrasaccharides, and 4-O-(glucopyranosyluronic acid)-L-fucose. The cleavage products from the methylated pectin were examined by g.l.c. and the partially methylated alditol acetates from the methylated carboxyl-reduced polysaccharide by g.l.c.-mass spectrometry. Parallel methylation studies on lemon-peel pectin have established a close similarity between the two pectins.     

Gelation of high methoxy pectin in the presence of pectin methylesterases and calcium

High methoxy pectin was submitted to various amounts of a fungal pectin methylesterase (PME) from Aspergillus aculeatus and of a plant PME from orange in the presence of calcium. The systems were characterized by rheological means during the gelation process. By the way of in situ demethoxylation with low amount of orange PME, it was possible to gel pectin from the beginning of the reaction although its high degree of methylation around 70. To understand this unusual properties, the behaviour of the two enzymes was investigated in pectic gels and in solution through the analysis of content and distribution of the remaining methyl esters. In the gel, the degree of methylation decreased slowly with orange PME and rapidly with Aspergillus PME. The degree of methylation and degree of blockiness after treatment with each PME in solution or in gels were slightly different. Possible explanations for this are evolving visco-elastic properties, including gel formation or influence of calcium on the enzyme–substrate complex.     

Kinetics of the pectin methylesterase catalyzed de-esterification of pectin in frozen food model systems

The pectin methylesterase (PME) catalyzed de-esterification of pectin was studied in four frozen food model systems based on sucrose, fructose, maltodextrin, and carboxymethylcellulose (CMC) in a temperature range from -24 to 20 degrees C, with the aim of elucidating the applicability of the theory of "food polymer science" on the kinetics. The rate substantially decreased around the glass transition temperature in the case of CMC, while very low rates were observed far above the glass transition temperature in the case of maltodextrin, fructose, and sucrose model systems. In general, the kinetics of this reaction was found to be influenced more by factors such as the characteristics of the component solutes, freeze concentration, the possible viscosity enhancement due to a particular combination of solutes, and the molecular size of the substrate molecule rather than the glass transition process. The Arrhenius equation described the temperature dependence of kinetics both in the liquid state of all the systems studied (r(2) > or = 0.97) and the glassy state of CMC (r(2) = 0.95). A clear break in the Arrhenius plot was observed as the temperature decreased to subfreezing temperatures. The Arrhenius equation could describe the kinetics reasonably well in the rubbery state for fructose and sucrose model systems (r(2) > 0.992). In the case of maltodextrin and CMC, the Arrhenius plots showed a slight curvature followed by a break at the glass transition temperature for CMC. The WLF equation with system-dependent coefficients better described the kinetics in the rubbery state of the CMC and part of the maltodextrin system. A linear relationship between the logarithm of the rate and T - Tg' described the kinetics in the sucrose as well as fructose model systems (r(2) = 0.9928 and 0.993, respectively).     

Modeling the kinetics of the pectin methylesterase catalyzed de-esterfication of pectin in frozen systems

The applicability of the William, Landel, and Ferry (WLF) equation with a modification to take into account the effect of melt-dilution and an empirical log-logistic equation were evaluated to model the kinetics of diffusion-controlled reactions in frozen systems. Kinetic data for the pectin methylesterase catalyzed hydrolysis of pectin in four model systems with different glass transition temperatures: sucrose, maltodextrin (DE = 16.5-19.5), carboxymethylcellulose (CMC) and fructose in a temperature range of -24 to 0 degrees C were used. The modified WLF equation was evaluated with a concentration-dependent glass transition temperature (T(g)) as well as the glass transition temperature of the maximally freeze-concentrated matrix (T(g)') as reference temperatures. The equation with temperature-dependent T(g) described the reaction kinetics reasonably well in all the model systems studied. However the kinetics was better described by a linear relationship between log(V(0)/V(0ref)) and (T - T(ref)) in all cases except CMC. The log-logistic equation also described the kinetics reasonably well. The effect of melt-dilution on reactant concentration was found to be minimal in all cases.     

Impact of pectin esterification on the antimicrobial activity of nisin‐loaded pectin particles

The relationship between pectin structure and the antimicrobial activity of nisin‐loaded pectin particles was examined. The antimicrobial activity of five different nisin‐loaded pectin particles, i.e., nisin‐loaded high methoxyl pectin, low methoxyl pectin, pectic acid, dodecyl pectin with 5.4 and 25% degree of substitution were tested in the pH range of 4.0–7.0 by agar‐diffusion assay and agar plate count methods. It was found that the degree of esterification of carboxyl group of galacturonic acid in pectin molecule is important for the antimicrobial activity of nisin‐loaded pectin particles. Nisin‐loaded particles prepared using pectic acid or the pectin with low degree of esterification exhibit higher antimicrobial activity than nisin‐loaded high methoxyl pectin particles. Pectins with free carboxyl groups or of low degree of esterification are the most suitable for particles preparation. Moreover, nisin‐loaded pectin particles were active at close to neutral or neutral pH values. Therefore, they could be effectively applied for food preservation. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 33:245–251, 2017     

Solution properties of pectin polysaccharides — III: Molecular size of heterogeneous pectin chains. Calibration and application of SEC to pectin analysis

Flax pectins, with a low anhydrogalacturonic acid content (AGA≤50%), have been studied by viscometry, light scattering and size exclusion chromatography. After removal of interfering superstructures, intrinsic viscosities were correlated with weight average molecular weights to give a Mark-Houwink coefficient a=0·69. The persistence length of these heterogeneous chains (PI: q=20–25 Å), compared with that of homogalacturonan ones previously studied (PII–PIII: q=67 Å), shows a higher segment density (branched conformation). Using a wide range of experimental data ((η), M_i, K_d) obtained on narrow pectic fractions of known composition, specific calibration curves of the Sephacryl 200/0·2 NaCl/Flax pectins (PI or PII–PIII) system were established. Applied to the indirect characterization of flax pectins, this size exclusion chromatography (SEC) system constitutes a very convenient method for analysing the molecular and macromolecular parameters ((η), M_w, M_n, I_p, ^UV) or for controlling the molecular weight distribution of pectins in flax cell walls during the physiological steps of growth and retting.     

Study of pectin esterase and changes in pectin methylation during normal and abnormal peach ripening

Peach fruit ( Prunus persica cv. Hermosa) were allowed to ripen immediately after harvest or after 30 days of 0°C storage. The fruits lost 75–80% of their firmness after 5 days at 20°C. During ripening after harvest there was a loss of both uronic acid and methyl groups from the cell wall. Cell wall labelling with JIM 7, a monoclonal antibody which recognized pectins with a high degree of methylation, was lower in ripe fruits than in freshly harvested fruits. However, ripe fruit cell walls did not cross-react with JIM 5, which recognizes pectins with low methylation. During storage, de-methylation occurred and in fruit ripened after storage there was little further change in pectin methylation or pectin content in the cell walls. The labelling of stored or stored plus ripened cell walls with JIM 7 was similar, but the cell walls of fruit ripened after storage showed some low cross-reactivity with JIM 5. The in vitro activity and mRNA abundance of pectin esterase (EC 3.1.1.11) was not correlated with the amount of de-esterification as measured chemically or by immuno-labelling in the cell walls. Eighty percent of the fruits which ripened after storage developed a woolly texture. It is suggested that woolliness is due to de-esterification of pectins, not accompanied by depolymerization, which leads to the formation of a gel-like structure in the cell wall.     

Capillary electrophoresis of homogeneous pectin fractions

Capillary electrophoresis (CE) has been used to characterize pectin fractions obtained from mother samples of varying degrees (and intramolecular patterns) of methylesterification (DM). These samples have been carefully produced by fractionation, (a) from the original mother samples on the grounds of molar mass, and (b) subsequently from the daughter fractions so obtained, on the grounds of charge. The results confirm theoretical predictions regarding the dependence of electrophoretic mobility on molar mass and DM and give further evidence that CE is able to give realistic information regarding the intermolecular DM of pectins.     

Crystal structure of plant pectin methylesterase

Pectin is a principal component in the primary cell wall of plants. During cell development, pectin is modified by pectin methylesterases to give different properties to the cell wall. This report describes the first crystal structure of a plant pectin methylesterase. The beta-helical structure embodies a central cleft, lined by several aromatic residues, that has been deduced to be suitable for pectin binding. The active site is found at the center of this cleft where Asp157 is suggested to act as the nucleophile, Asp136 as an acid/base and Gln113/Gln135 to form an anion hole to stabilize the transition state.     

An array of possibilities for pectin

Pectins are a major component of plant cell walls and have numerous roles in plant growth and development. Extracted pectins are widely used as functional food ingredients in products including ice creams, jams, jellies and milk drinks. Although all are based on a galacturonan-rich backbone, pectins are an immensely diverse family of polysaccharides, the functional properties of which are dictated by their fine structures. Understanding the biological roles of pectins and optimizing their industrial usage requires a detailed knowledge of their diversity and spatial and temporal distributions, and microarray technology is a promising tool for high throughput pectin analysis. This article discusses the technical aspects of the production of pectin microarrays and explores their current and potential future uses in the context of recent work in the field.     

Gel permeation chromatography of sunflower pectin

Sunflower pectin has been fractionated on Sepharose 2B/Sepharose 4B. Molecular weights were measured within the eluate by light scattering and intrinsic viscosities to establish a universal calibration line, e.g. a plot of the logarithm of the product of the weight-average molecular weight and the intrinsic viscosity against the elution volume. It was found that the universal calibration line of pectin differs, if only modestly, from those of dextran and dextran sulphate. Intrinsic viscosities and molecular weights do not correlate in the region of high molecular weights concerning about 15% of the sample. In most instances with molecular weights below 100 000 a Mark-Houwink relation of $\text{[η] = 0·0851}\text{M}{}_{\mathrm{<mtext>w</mtext>}}{}^{\mathrm{0·68}}$ is valid.     

Mesoscopic structure of pectin in solution

Mesoscopic structure of pectin with different molecular characteristics was investigated by means of small angle X‐ray scattering (SAXS), electrokinetic measurements and data modelling. The influence of a broad range of pH (2–7) on chain conformation in the dilute and semi‐diluted regime was investigated. Scattering data and concomitant analysis revealed two length scales at all environmental conditions studied. pH showed greater influence at acidic values (pH 2.0) enhancing the globular component of the structure due to association of galacturonic acid residues. Double logarithmic scattering intensity plots revealed fractal dimensions of 1.9 ± 0.2 in the low‐q regime and 1.5 ± 0.2 in the high q‐region, irrespectively of the specific environment. Increase in branching of RG‐I regions of the polysaccharide chains enhanced the compact conformation irrespectively of the pH or concentration. The present work shows that radical changes in pectin conformation can be induced only under strongly acidic conditions a finding that has important consequences in tailoring the technological performance of these biopolymers.     

Current views on pectin substances

This review concerns pectin substances, the most complex class of plant polysaccharides. For the most part, the data reported after 1998 are presented; the references to earlier works are made only in the historical aspect. New data on the structure of pectin substances, their physiological activity, their role in plants, and their valuable physical properties are surveyed.     

Material properties of concentrated pectin networks

We have examined the mechanical behaviour of different types of pectin at high concentrations (> 30% w/w), relevant to the behaviour of pectin in the plant cell wall, and as a film-forming agent. Mechanical properties were examined as a function of counterion type (K(+), Ca(2+), Mg(2+)), concentration and extent of hydration. Hydration was controlled in an osmotic stress experiment where pectin films were exposed to concentrated polyethylene glycol [PEG] solutions of known osmotic pressure. We investigated the mechanical behaviour under simple extension. The results show that the swelling and stiffness of the films are strongly dependent on pectin source and ionic environment. At a fixed osmotic stress, both Ca(2+) or Mg(2+) counterions reduce swelling and increase the stiffness of the film.