Soft Matter Approaches Research Articles

Soft matter approach for creating novel protein hydrogels using fractal whey protein assemblies as building blocks

In this study, mesoscopic sized fractal assembly (FA) particles were prepared using whey protein isolate; the cold-set gelation properties of FA particles were investigated in-depth. Two types of FA particles (FA-62 and FA-90) with different mean sizes were synthesized through controlled thermal treatment of whey protein solutions at two concentrations (62 g/L and 90 g/L). Particle characteristics e.g. hydrodynamic radius, ζ-potential and surface hydrophobicity were dependent on pH and structure of FA. Transmission electron microscopy (TEM) observation confirmed the fractal morphology and small-angle X-ray scattering (SAXS) analysis suggested an internal fractal structure for the obtained FA particles. Eight cold-set FA protein gels (2 % w/v) were manufactured by controlling two gelling factors at two levels: pH (5.8 and 7.0) and Ca2+ content (5 mM and 10 mM). Rheological characteristics in the large amplitude oscillatory shear regime revealed that pH 7.0 gels were softer and elastic while pH 5.8 gels were harder and brittle. Rheology Pipkin diagrams demonstrated that the strain softening/stiffening and the shear-thinning/thickening behaviors may be fine-tuned by manipulating the key gelation factors: e.g. FA structure, pH, and Ca2+. The entrainment speed-dependent friction coefficient curves showed that at an intermediate velocity regime (6–250 mm s−1), FA-90 particles induced hydrogels had superior lubrication effect compared to FA-62 gels. This work demonstrated a food structure design approach regarding tuning texture and lubrication properties of protein gels without changing protein content and protein composition. The optimized protein hydrogels may be used as texturizer for “cleaner label” food formulas and/or as delivery system for carrying micronutrients.

Active forces shape the metaphase spindle through a mechanical instability

The metaphase spindle is a dynamic structure orchestrating chromosome segregation during cell division. Recently, soft matter approaches have shown that the spindle behaves as an active liquid crystal. Still, it remains unclear how active force generation contributes to its characteristic spindle-like shape. Here we combine theory and experiments to show that molecular motor-driven forces shape the structure through a barreling-type instability. We test our physical model by titrating dynein activity in Xenopus egg extract spindles and quantifying the shape and microtubule orientation. We conclude that spindles are shaped by the interplay between surface tension, nematic elasticity, and motor-driven active forces. Our study reveals how motor proteins can mold liquid crystalline droplets and has implications for the design of active soft materials.

Soft condensed matter physics of foods and macronutrients

Understanding food properties is paramount for enhancing features such as appearance, taste and texture, for improving health-related factors such as minimizing the onset of allergies or improving the digestibility of nutrients, and for preserving food and extending its shelf-life. This Review discusses the challenges and opportunities offered by analysing foods as soft condensed matter systems. Emphasis is placed on the three main macronutrients constituting the main building blocks of foods: polysaccharides, proteins and lipids. Similarities and differences with synthetic polymers, colloids and surfactants are described. This Review also discusses the lessons that can be learned from soft matter approaches and the extent of their applicability to real foods. This Review tackles how soft condensed matter physics can assist in the understanding of complex food systems, by relying on the foundations of established theories on polymers, colloids and surfactants to unravel the properties of food macrocomponents and the challenges associated with this task.

Predictions of the shear modulus of cheese, a soft matter approach

Abstract The rheological and structural properties of cheese govern many physical processes associated with cheese such as slumping, slicing and melting. To date there is no quantitative model that predicts shear modulus, viscosity or any other rheological property across the entire range of cheeses; only empirical fits that interpolate existing data. A lack of a comprehensive model is in part due to the many variables that can affect rheology such as salt, pH, calcium levels, protein to moisture ratio, age and temperature. By modelling the casein matrix as a series core-shell nano particles assembled from calcium and protein these variables can be reduced onto a simpler two-dimensional format consisting of attraction and equivalent hard sphere volume fraction. Approximating the interaction between core-shell nano particles with a Mie potential enables numerical predictions of shear moduli. More qualitatively, this two-dimensional picture can be applied quite broadly and captures the viscoelastic behaviour of soft and hard cheeses as well as their melting phenomena.

Proteins for the future: A soft matter approach to link basic knowledge and innovative applications

• Protein interactions play a key role in determining the final structure and properties of products.

Probing the organization of fulvic acid using a cationic surfactant

Abstract The organization of Suwannee River Fulvic Acid (SRFA) is investigated through the interaction of SRFA with a cationic surfactant molecule (Dodecyl-trimethylammonium chloride (DTAC)). Turbidity measurements, Dynamic light scattering, electrophoretic mobility, surface tension, and cryo-transmission electron microscopy are combined to describe the SRFA/DTAC molecular structures thus obtained. Increasing DTAC concentration, fulvic acid-rich unilamellar vesicles, globules, aggregates of globules, disks, DTAC-rich unilamellar vesicles, and loosely aggregated spheroidal structures, are successively observed. Such sequence of molecular structures is typically found in phase diagrams of catanionic systems (mixture of oppositely charged surfactants). The strong surface activity of fulvic acid/DTAC complexes and the geometrical constraints associated with the formation of vesicles imply that a major component of SRFA is an individual amphiphile negatively charged of molecular size similar to that of DTAC. This soft matter approach supports a supramolecular organization for SRFA.

Soft Matter Approaches for Enhancing the Catalytic Capabilities of Polyoxometalate Clusters

In this minireview, we discuss the recent efforts on expanding the catalytic capabilities of polyoxometalates (POM) through emulsion catalysis approaches with novel catalytic-active POM–organic hybrid clusters as emulsifiers. The hybrid emulsifiers include surfactant encapsulated POM complexes, molecular POMs–organic hybrids, and POM-based solid nanoparticles. With such novel approaches the catalytic efficiency of the POMs can be significantly improved by enhancing the compatibility of the POMs with organic media, providing catalytic interface for biphasic reactions, as well as easier preparation, and better recyclability. Particularly, a simple, green chemistry method to prepare metal nanoparticle materials with POMs as both reducing and capping agents in aqueous is reviewed.

Soft matter approaches as enablers for food macroscale simulation

Macroscopic deformable multiphase porous media models have been successful in describing many complex food processes. However, the properties needed for such detailed physics-based models are scarce and consist of primarily empirical models obtained from experiment. Likewise, driving forces such as swelling pressure have also been approached empirically, without physics-based explanations or prediction capabilities. Soft matter based prediction of properties will provide an additional avenue to obtaining properties and also provide a deeper and critical understanding of how these properties change with composition, temperature and other process variables.

Soft matter approaches to structured foods: from “cook-and-look” to rational food design?

Developments in soft matter physics are discussed within the context of food structuring. An overview is given of soft matter-based approaches used in food, and a relation is established between soft matter approaches and food technology, food creation, product development and nutrition. Advances in food complexity and food sustainability are discussed from a physical perspective, and the potential for future developments is highlighted.