Incorporation of bioactive compounds–such as vitamins, probiotics, bioactive peptides, and antioxidants etc.–into food systems provide a simple way to develop novel functional foods that may have physiological benefits or reduce the risks of diseases. As a vital macronutrient in food, proteins possess unique functional properties including their ability to form gels and emulsions, which allow them to be an ideal material for the encapsulation of bioactive compounds. Based on the knowledge of protein physical–chemistry properties, this review describes the potential role of food proteins as substrate for the development of nutraceutical delivery systems in the form of hydrogel, micro-, or nano- particles. Applications of these food protein matrices to protect and delivery-sensitive nutraceutical compounds are illustrated, and the impacts of particle size on release properties are emphasized.

Food protein-based materials as nutraceutical delivery systems

A general peptide design is presented that links the pH-dependent intramolecular folding of β-hairpin peptides to their propensity to self-assemble, affording hydrogels rich in β-sheet. Chemical responsiveness has been specifically engineered into the material by linking intramolecular folding to changes in solution pH, and mechanical responsiveness, by linking hydrogelation to self-assembly. Circular dichroic and infrared spectroscopies show that at low pH individual peptides are unstructured, affording a low-viscosity aqueous solution. Under basic conditions, intramolecular folding takes place, affording amphiphilic β-hairpins that intermolecularly self-assemble. Rheology shows that the resulting hydrogel is rigid but is shear-thinning. However, quick mechanical strength recovery after cessation of shear is observed due to the inherent self-assembled nature of the scaffold. Characterization of the gelation process, from the molecular level up through the macroscopic properties of the material, suggests ...

Responsive Hydrogels from the Intramolecular Folding and Self-Assembly of a Designed Peptide

Protein-based hydrogels are used for many applications, ranging from food and cosmetic thickeners to support matrices for drug delivery and tissue replacement. These materials are usually prepared using proteins extracted from natural sources, which can give rise to inconsistent properties unsuitable for medical applications. Recent developments have utilized recombinant DNA methods to prepare artificial protein hydrogels with specific association mechanisms and responsiveness to various stimuli. Here we synthesize diblock copolypeptide amphiphiles containing charged and hydrophobic segments. Dilute solutions of these copolypeptides would be expected to form micelles; instead, they form hydrogels that retain their mechanical strength up to temperatures of about 90 degrees C and recover rapidly after stress. The use of synthetic materials permits adjustment of copolymer chain length and composition, which we varied to study their effect on hydrogel formation and properties. We find that gelation depends not only on the amphiphilic nature of the polypeptides, but also on chain conformations--alpha-helix, beta-strand or random coil. Indeed, shape-specific supramolecular assembly is integral to the gelation process, and provides a new class of peptide-based hydrogels with potential for applications in biotechnology.

Rapidly recovering hydrogel scaffolds from self-assembling diblock copolypeptide amphiphiles

Molecular simulations are performed to study the self-assembly of particles with discrete, attractive interaction sites − “patches” − at prescribed locations on the particle surface. Chains, sheets, rings, icosahedra, square pyramids, tetrahedra, and twisted and staircase structures are obtained through suitable design of the surface pattern of patches. Our simulations predict that the spontaneous formation of two-dimensional sheets and icosahedra occurs via a first-order transition while the formation of chains occurs via a continuous disorder-to-order transition as in equilibrium polymerization. Our results show how precise arrangements of patches combined with patch “recognition” or selectivity may be used to control the relative position of particles and the overall structure of particle assemblies. In this context, patchy particles represent a new class of building block for the fabrication of precise structures.

/pdf/self-assembly-of-patchy-particles-1ayk07rbs2.pdf

Self-Assembly of Patchy Particles.

Over the past century, hydrogels have emerged as effective materials for an immense variety of applications. The unique network structure of hydrogels enables very high levels of hydrophilicity and biocompatibility, while at the same time exhibiting the soft physical properties associated with living tissue, making them ideal biomaterials. Stimulus-responsive hydrogels have been especially impactful, allowing for unprecedented levels of control over material properties in response to external cues. This enhanced control has enabled groundbreaking advances in healthcare, allowing for more effective treatment of a vast array of diseases and improved approaches for tissue engineering and wound healing. In this extensive review, we identify and discuss the multitude of response modalities that have been developed, including temperature, pH, chemical, light, electro, and shear-sensitive hydrogels. We discuss the theoretical analysis of hydrogel properties and the mechanisms used to create these responses, highlighting both the pioneering and most recent work in all of these fields. Finally, we review the many current and proposed applications of these hydrogels in medicine and industry.

/pdf/stimulus-responsive-hydrogels-theory-modern-advances-and-20f2g2ofnl.pdf

Stimulus-responsive hydrogels: Theory, modern advances, and applications

Rheological characterisation of polymer gels

Globular protein gelation - theory and experiment

Heat-induced gelation of globular proteins: part 3. Molecular studies on low pH β-lactoglobulin gels

Particulate gels, especially those formed from heating protein solutions, have been extensively investigated over the years. One focus of this work has been, for commercial reasons, on rather crude mixtures of the main milk protein components (whey isolates), β-lactoglobulin and α-lactalbumin. Moreover, most previous work has concentrated on examining structural and rheological properties of fully cured gels. In the present paper, a less pragmatic approach is adopted, and the gelation behavior of solutions of relatively pure β-Lg (under isothermal heating at 80 °C) are investigated over a range of concentrations and pH values (7, 3, 2.5, and 2). Both gel time and limiting (extrapolated) long-time modulus data were measured and were considered in light of currently available models for the gelation process. Whereas the gel time data was described best by a semiempirical model introduced by one of the authors, the modulus data could be quite adequately understood in terms of branching theory (cascade theory...

Heat-Induced Gelation of Globular Proteins: 4. Gelation Kinetics of Low pH β-Lactoglobulin Gels

Mixed globular protein gels, or gel composites, based on heating solutions of proteins from milk have been investigated for many years, although the great majority of these studies have used rather crude whey isolates containing a fixed ratio of the principal components β-lactoglobulin and α-lactalbumin and some denatured material. Moreover, most of the previous work has concentrated on examining structural and rheological properties of fully cured gels. In the present paper, attention is focused on well-defined mixtures composed of much purer samples of the principal components, these being present in systematically varying proportions. Protein−protein co-gels are formed at pH's 3 and 7, by heating the mixtures at 80 °C. Gelation is monitored by cure curve measurement and both gel times and long-time limiting moduli established. A considerable difference in behavior is observed at the two pH's and modeling based on segregated phase-separated structures gives only a partial explanation of the results. It ...

Gaynor M. Kavanagh

Papers

Rheological characterisation of polymer gels

Globular protein gelation - theory and experiment

Heat-induced gelation of globular proteins: part 3. Molecular studies on low pH β-lactoglobulin gels

Heat-Induced Gelation of Globular Proteins: 4. Gelation Kinetics of Low pH β-Lactoglobulin Gels

Heat-induced gelation of β-lactoglobulin/α-lactalbumin blends at pH 3 and pH 7