Using SAXS to reveal the degree of bundling in the polysaccharide junction zones of microrheologically distinct pectin gels.

The results of microrheological studies carried out on ionotropic pectin gels, particularly the manifest power law behavior observed at high frequencies, indicate that by using different assembly conditions gels can be formed in which the elementary network strands have different stiffnesses. It has been hypothesized that these differences reflect different network architectures, the extreme cases of which might be described as (i) dimeric calcium-chelating junction-zones of limited extent, linked by considerably longer, flexible, single-chain sections, or (ii) semiflexible bundles consisting of extensively aggregated dimeric junction zones that latterly become entangled and cross-linked. To test this hypothesis directly, microrheologically distinct pectin gels have been generated using different assembly modalities, in particular by using different concentrations of polymer and cross-linking ions and by contrasting the controlled-release of ions or ion-binding groups, and the resulting systems have been studied by small-angle X-ray scattering.

Extracting intramolecular sequence information from intermolecular distributions: highly nonrandom methylester substitution patterns in homogalacturonans generated by pectinmethylesterase.

The ratio of the two component sugar residues comprising the anionic polysaccharide homogalacturonan (HG; namely, methylesterified or unmethylesterifed galacturonic acid (GalA)) has been controlled chemically or enzymatically in order to produce samples comprised of varying degrees and distributions of methylesterification (DM). Capillary electrophoresis (CE) has been used to characterize the samples produced and, by mapping the measured electrophoretic mobilities to biopolymer charge density, intermolecular distributions of the DM have been extracted. For chemically modified samples with random intramolecular patterns of methylesterification, the experimentally extracted intermolecular DM distributions agree well with the predictions of calculations based on the binomial theorem, demonstrating that the random nature of the demethylesterification process and, hence, the intramolecular DM patterns themselves, are directly reflected in the intermolecular distribution.

Probing the interaction between recombinant human myelin basic protein and caseins using surface plasmon resonance and diffusing wave spectroscopy.

An intrinsically unstructured human myelin basic protein (hMBP) was expressed in the milk of transgenic cows (TGmilk) and found exclusively associated with the casein micellar phase. The interaction between the recombinant protein and milk caseins was investigated using surface plasmon resonance (SPR). An anti-human myelin basic protein antibody was covalently immobilized to the surface of the sensor chip.

Multiple particle tracking investigations of acid milk gels using tracer particles with designed surface chemistries and comparison with diffusing wave spectroscopy studies.

Multiple particle tracking (MPT) has been used in an attempt to probe the heterogeneity of acid milk gels, made with and without added pectin, by following the distribution of the displacements of added tracer beads during and after gelation using the Van Hove distribution. Furthermore, the surface chemistry of the latex probe particles was modified in an attempt to control their location in the system and probe the microrheological properties of the protein network and aqueous-phase voids independently. In addition, the mean square displacement (MSD) of the casein micelles/casein aggregates themselves, obtained by diffusing wave spectroscopy (DWS), has been compared to the ensemble-averaged MSD calculated from the data obtained by tracking the movement of the added tracers, with and without a kappa-casein coating.

Electrophoretic behavior of copolymeric galacturonans including comments on the information content of the intermolecular charge distribution.

Capillary electrophoresis has been used to characterize samples of the copolymeric anionic polysaccharides homo- and rhamno-galacturonan (HG and RGI, respectively). In the case of HG, the ratios of the two component sugar residues, galacturonic acid and its methylesterified analogue, have been controlled chemically to produce samples comprised of varying degrees of methylesterification (DM). The mapping of the measured electrophoretic mobilities to the biopolymer charge density has been considered in some detail and for HG substrates with random intramolecular patterns of methylesterification it is shown that the experimentally extracted intermolecular DM distribution agrees well with the predictions of calculations based on the binomial theorem.