Polysaccharide Nanostructures

Polysaccharides are carbohydrate polymers where sugar units are linked together through glycosidic linkages. In living organisms polysaccharides are the structural polymers that provide support (e.g., cellulose in plants or chitin in arthropods) or the sources of energy for plant development (e.g., starch). Polysaccharides are routinely used in the food industry, most frequently as thickeners, stabilizers of dispersions (emulsions, foams) or structuring agents of water and air

Calculation of Relaxation Spectra from Stress Relaxation Measurements

Application of stress on materials increases the energy of the system. After removal of stress, macromolecules comprising the material shift towards equilibrium to minimize the total energy of the system. This process occurs through molecular rearrangements or “relaxation” during which macromolecules attain conformations of a lower energetic state. The time, however, that is required for these rearrangements can be short or long depending on the interactions between the macromolecular species that consist the material. When rearrangements occur faster than the time of observation (experimental timescale) then molecular motion is observed (flow) and the material is regarded as viscou

Polysaccharides at fluid interfaces of food systems

Fabrication of next generation polysaccharides with interfacial properties is driven by the need to create high performance surfactants that operate at extreme environments, as for example in complex food formulations or in the gastrointestinal tract. The present review examines the behaviour of polysaccharides at fluid food interfaces focusing on their performance in the absence of any other intentionally added interfacially active components. Relevant theoretical principles of colloidal stabilisation using concepts that have been developed for synthetic polymers at interfaces are firstly introduced. The role of protein that in most cases is present in polysaccharide preparations either as contaminant or as integral part of the structure is also discussed. Critical assessment of the literature reveals that although protein may contribute to emulsion formation mostly as an anchor for polysaccharides to attach, it is not the determinant factor for the long-term emulsion stability, irrespectively of polysaccharide structure. Interfacial performance of key polysaccharides is also assessed revealing shared characteristics in their modes of adsorption. Conformation of polysaccharides, as affected by the composition of the aqueous solvent needs to be closely controlled, as it seems to be the underlying fundamental cause of stabilisation events and appears to be more important than the constituent polysaccharide sugar-monomers. Finally, polysaccharide adsorption is better understood by regarding them as copolymers, as this approach may assist to better control their properties with the aim to create the next generation biosurfactants

Linear viscoelasticity of gluten: decoupling of relaxation mechanisms

The influence of water content on the relaxation dynamics of mesoporous gluten networks has been explored in a wide range of temperatures. The systems were investigated in the linear viscoelastic region by means of stress relaxation, creep and numerical analysis of data. Time-temperature superposition principle and sticky reptation dynamics have been used to provide molecular interpretation of gluten relaxation. Overall, hydration influences relaxation behaviour of the system, which can be linked to changes in the secondary structure of gluten proteins with increase in water content. Relaxation spectra calculated with Tikhonov regularization revealed the remarkable influence of water on the long times relaxation processes of the material. Creep measurements and extraction of dynamic data with direct conversion of creep data via Laplace transform augmented the experimental timeframe of observations to low frequencies unattainable by standard frequency sweeps. The predominance of loss modulus at long times is attributed to migration of water within the nanopores of the structure. Samples also exhibit self-similar relaxation a characteristic of systems existing at a critical state. Two relaxation mechanisms can be distinguished: one arising from viscoelastic relaxation of protein chains and an additional stemming from poroelastic relaxation owing to migration of water in the system

Modeling and fundamental aspects of structural relaxation in high-solid hydrocolloid systems

The structural relaxation properties of high-solid gelling polysaccharides, gelatin and whey protein with small-molecule co-solutes have been reviewed focusing on the glass transition region and glassy state of the mechanical master curve. Compliance with the principle of thermorheological simplicity is established allowing horizontal superposition of viscoelastic functions in the form of small-deformation stress relaxation or dynamic oscillation modulus. Numerical calculations via the Tikhonov regularization yield smooth stress relaxation spectra over a broad timescale that encompasses the isothermal process of vitrification in these systems. Next, the molecular coupling theory addressed the polymer chain dynamics of the local segmental motions that determine the glass transition temperature (Tg) of condensed matrices. Thus a more complete picture of the physics of intermolecular interactions in the short-time region of the glass dispersion has emerged. It allows estimation of the relaxation time for local segmental motions at Tg, and the extent of cooperativity between adjacent chemical moieties governing kinetics of viscoelastic relaxation in hydrocolloid based systems at the glass transition region

DDASaccident501

At approx. 0855 Hrs on Tuesday 11th September 2001 the deminer [the Victim] was fatally injured while performing manual demining duties for [International demining NGO]. The accident was caused by the accidental detonation of Pt Mi Ba III anti-tank mine. It should be noted that the casualty had been accepted to participate in the next Team Leaders course. At the commencement of the shift he was congratulated by all members of GS8 for being accepted for a demining team leader course. He was extremely happy on the day of the accident. He was married with one child and had no history of depression

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 biopolymer

In situ rheological measurements of the external gelation of alginate

Direct mixing of alginate and divalent cations such as Ca2+ generally produces heterogeneous gels that form almost instantaneously. Therefore, is particularly difficult to measure the rheological properties of this gelation event due to the rapid gelation kinetics. In this study, the gelation of alginate when exposed to a solution of CaCl2 was measured by using a modified rheometer. This modification involved attaching a petri dish to the lower plate of the rheometer into which, filter paper impregnated with CaCl2 solution was added. A semi-permeable membrane was then placed above the filter paper as a barrier to prevent the filter paper imbibing the gel. Samples of 4%w/w alginate were loaded onto the semi-permeable membrane and measurements were taken using 55mm parallel plate geometry. Measurements of G′ and Gʺ were determined as a function of time to monitor gelation. Once gelation was complete the filter paper was removed and replaced with filter paper impregnated with calcium chelators (EDTA, sodium citrate) to assess the degradation of the gel. The results showed that this technique was suitable for analysing the external gelation of alginate with a sharp increase in G′ in the first three minutes which then plateaued over the remainder of the test. It was also shown that gel stiffness reduced to a greater extent on exposure to EDTA compared with sodium citrate. This method is not only suitable for measuring rapid gelation kinetics on exposure to cross-linkers, but has potential applications in modelling the in situ gelation behaviour in simulated physiological environments

Techno-Economic Assessment of Polysaccharide Extraction from Baobab: A Scale Up Analysis

This research studied the commercial exploitation of an indigenous African crop in order to formulate high value products, with a potential significant impact on the local economy. More specifically, the present work investigated the extraction of polysaccharides from baobab in a bench-scale unit, focusing on the overall yield and the techno-economic assessment of the extraction process. Preliminary technoeconomic analysis for two scenarios (with and without ethanol recycling) was performed to determine the economic viability of the process and the development of the baobab market both in Nigeria and the UK. A full economic analysis was undertaken for each of the two scenarios, considering all operating and capital costs, and the production cost of baobab polysaccharides was estimated based on a constant return on investment. Combining the operating cost with the average polysaccharide yield, the minimum profitable selling price in the UK was estimated to be between £23 and £35 per 100 g of polysaccharide, which is comparable to the commercial selling price of high purity polysaccharides. An assessment of a scaled-up plant was also performed under Nigerian conditions and the results showed that such an investment is potentially viable and profitable, with a minimum profitable selling price of £27 per 100 g, a value comparable to the UK-based scenarios

Pectin isolation and characterization from six okra genotypes

Pectin was isolated by aqueous extraction at pH 6.0 from the pods of six different okra genotypes (Abelmoschus esculentus L.). Genetic diversity was determined using fragment length analysis (FLA) of ten simple sequence repeat (SSR) markers. Physical and chemical evaluation of pectin was performed by means of FT-IR and NMR spectroscopy, sugar composition analysis (GC-MS), size exclusion chromatography coupled to multi-angle laser light scattering (SEC-MALLS), dilute solution viscometry and steady shear rheology assisted by principal component analysis (PCA). Each of the SSR markers detected on average 4.1 alleles and revealed unique genotypes for each sample. Extraction yield was between 11 and 14% resulting in pectin with galacturonic acid content between 43 and 63%, low degree of methyl-esterification (17–25%) and high degree of acetylation (20–40%). All samples were of high weight-average molar mass (Mw) (700–1700 × 103 g mol−1) and sugar composition analysis revealed the structural diversity of samples with HG/RG-I ratios ranging between 1.3 and 3.1. The present work shows that individual okra genotypes provide pectin with different structural properties that could potentially provide a new source of functional pectin for the food or pharmaceutical industries