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

Temperature dependence of relaxation spectra for highly hydrated gluten networks

In the present investigation, the temperature dependence (0e50 �C) of the relaxation spectrum of hydrated gluten was studied using novel numerical algorithms. Tikhonov regularization, in conjunction with the L-curve criterion for optimal calculation of the regularization parameter, was used to generate the relaxation spectrum from stress relaxation measurements on shear. The methodology used revealed six molecular events with baseline resolution that could be grouped into fast- and slow-relaxation regimes. The fast-relaxation regime exhibited strong temperature dependence whereas the slow one is temperature independent indicating on the whole two dominant mechanisms of interactions. The “loop and train” structural model for gluten interactions was found adequate to describe the relaxation events in this system, with the fast regime being assigned to interactions due to hydrogen bonding whereas the slow one to permanent cross-linking of the entire network. Findings of the present investigation provide fundamental understanding and give new insights into the complexity of interactions and relaxation modes of hydrated gluten

Numerical computation of relaxation spectra from mechanical measurements in biopolymers

In the present investigation, a computational methodology to treat relaxation spectra from mechanical data is developed. To calculate the spectral function that represents the relaxation process of the material, three different regularization algorithms were tested using MATLAB. Two algorithms employ Tikhonov’s regularization whereas the third investigative tool is an implementation of the CONTIN algorithm. These efforts improved the ability to look at data hence allowing utilization of the L-curve criterion in order to locate the optimum regularization parameter for accurate data inversion. Algorithms were first evaluated with hypothetical data followed by experimental datasets of hydrated gluten as a model biopolymer system. Essentially, algorithms converge on a specific relaxation spectrum that unveils the molecular features of gluten structure. The methodology described is not limited to mechanical measurements but should be used with any type of exponential decay in studies of relaxation processe

Combined use of the free volume and coupling theories in the glass transition of polysaccharide/co-solute systems

The structural properties of the glass dispersion in agarose, �-carrageenan and deacylated gellan with co-solute (glucose syrup) at 80.0% (w/w) solids were studied. Investigative techniques were smalldeformation stress relaxation and dynamic oscillation on shear. Vitrification was monitored between −2 and −50 ◦C with continuous thermal runs and isothermal frequency or time sweeps obtained at constant temperature intervals. The time–temperature superposition principle was utilized to compose master curves. The Williams, Landel and Ferry equation was able to pinpoint the network Tg for these systems as the turning point from the predictions of the free volume theory in the transition region to those of the reaction rate theory at the glassy state. Further insights into the physics of intermolecular interactions at the vicinity of Tg were obtained using the coupling model of molecular dynamics in the form of the Kohlrausch, Williams and Watts function. The model described well the spectral shape of the local segmental motions in polysaccharide/co-solute samples at the short-time region of the stress–relaxation master curve. Analysis provided the intermolecular interaction constant and apparent relaxation time, which are valuable parameters for the elucidation of structural morphology at Tg

Molecular Functionality of Plant Proteins from Low- to High-Solid Systems with Ligand and Co-Solute

In the food industry, proteins are regarded as multifunctional systems whose bioactive hetero-polymeric properties are affected by physicochemical interactions with the surrounding components in formulations. Due to their nutritional value, plant proteins are increasingly considered by the new product developer to provide three-dimensional assemblies of required structure, texture, solubility and interfacial/bulk stability with physical, chemical or enzymatic treatment. This molecular flexibility allows them to form systems for the preservation of fresh food, retention of good nutrition and interaction with a range of microconstituents. While, animal- and milk-based proteins have been widely discussed in the literature, the role of plant proteins in the development of functional foods with enhanced nutritional profile and targeted physiological effects can be further explored. This review aims to look into the molecular functionality of plant proteins in relation to the transport of bioactive ingredients and interaction with other ligands and proteins. In doing so, it will consider preparations from low- to high-solids and the effect of structural transformation via gelation, phase separation and vitrification on protein functionality as a delivery vehicle or heterologous complex. Applications for the design of novel functional foods and nutraceuticals will also be discussed

Effect of aging and ice-structuring proteins on the physical properties of frozen flour–water mixtures

The present work investigates the effect of aging and ice-structuring proteins at low levels of solids (0.1% w/w) on the physical properties of frozen flour–water mixtures (37.5% w/w moisture). Differential scanning calorimetry, nuclear magnetic resonance, dynamic oscillation on shear, creep testing and electron microscopy were employed to explore the underlying molecular aspects of dough deterioration. Starch granules are embedded in a continuous rather than a fibrous gluten network and it was found that in such a system ice recrystallization as opposed to cryo-dehydration is the mechanism responsible for alteration of the structural characteristics of the material on storage. Deterioration of the mechanical properties continued unabated for 30 days of aging with the ice-structuring proteins being unable to offer protection against recrystallization at the concentration level studied (0.1% w/w). Furthermore, storage near the melting point of ice of the flour–water sample was found to accelerate the structural losses owing to increasing water mobility at this regime