Mesoscopic structure of pectin in solution

Abstract

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.

Structure-Function Relationships in Pectin Emulsification

“…It has been shown that RG-I segments impart greater flexibility to the pectin chains [ 23 ]. In particular, persistence length that can used as a measure of chain flexibility has been found to be lower for okra pectin chains with greater content in RG-I regions [ 24 ]. Consequently, the additional flexibility of the chains creates shorter separation distances between droplets resulting in ineffective steric stabilization compared to those with lower amounts of RG-I (Fig.…”

The primary, secondary, and structures of higher levels of pectin polysaccharides

“…The low pH decreases the biopolymer charge due to the protonation of the carboxyl groups of the GalA residues and therefore aggregation is more intensive at very low pH values due to the neutralization of the chains (Gilsenan et al., 2000). It has been demonstrated for pectin extracted from okra that at a low pH, the chain has a compact conformation whereas high pH values result in an extended conformation (Alba, Bingham, & Kontogiorgos, 2017; Alba, Kasapis, & Kontogiorgos, 2015a). For the main pectin sources, that is citrus, apple, and sugar beet, the pectin conformation is semiflexible (Axelos & Thibault, 1991; Cros et al., 1996; Garnier, Axelos, & Thibault, 1993; Morris, Ralet, Bonnin, Thibault, & Harding, 2010), that is the persistence length is of the order of 10 to 17 monomers (Dumitriu, 2004).…”

“…For the main pectin sources, that is citrus, apple, and sugar beet, the pectin conformation is semiflexible (Axelos & Thibault, 1991; Cros et al., 1996; Garnier, Axelos, & Thibault, 1993; Morris, Ralet, Bonnin, Thibault, & Harding, 2010), that is the persistence length is of the order of 10 to 17 monomers (Dumitriu, 2004). The neutral sugars on the side of the RGI backbone are not influenced by pH and serve as the basis for compact conformations over the entire range of pH (Alba et al., 2017; Morris et al., 2008). Therefore, the coil‐type conformation depends on the degree of branching by neutral sugars.…”

“…For instance, apple or sugar beet pectins, due to their more branching structure, are more flexible than citrus even with the same DM (Dumitriu, 2004). For obvious reasons, RG‐I pectins are usually more compact and more flexible with a random coil conformation as opposed to those rich in smooth HG regions (Alba et al., 2017, 2018; Morris & Ralet, 2012; Ralet et al., 2008). The maximum degree of flexibility is obtained at a DM ∼50% and probably occurs as result of the interplay between hydrophobic and hydrophilic interactions which are favored at high and low degrees of methylation, respectively (Dumitru, 2004).…”

Structural and rheological studies of a polysaccharide mucilage from lacebark leaves (Hoheria populnea A. Cunn.)

“…6C). The uronic acid components of the polysaccharides found in mucilages from the Malvaceae have a negative charge at neutral pH, which can cause intra-molecular repulsion resulting in an extended conformation [46,47]. This favours inter-molecular interactions between the chains rather than self-association.…”