Heat- and shear-reversible networks in food: A review.

While nature behaves like an irreversible network with respect to entropy and time, certain systems in nature exist that are, to some extent, reversible. The property of reversibility imparts unique benefits to systems that possess them, making them suitable for designing self-healing, stimuli-responsive, and smart materials that can be used in widely divergent fields. Reversible networks are currently being exploited for applications in tissue engineering, drug delivery, and soft robotics. They are also being utilized as low-calorie fat mimetics with melt-in-your-mouth textures, as well as being explored as potential scaffolds for three-dimensional (3D) printable food, among other applications. This review aims to gather representative examples of heat- and shear-reversible networks in the food science literature from the last 30 or so years, in other words, reversible food gels made either from linear biopolymers or from colloidal, particulate dispersions, including those that have been modified specifically to induce reversibility. An overview of the network mechanisms involved that impart reversibility, including a discussion of the strength and range of forces involved, will be highlighted. A model that explains why certain networks are thermoreversible while others are shear-reversible, and why others are both, will also be proposed. A fundamental understanding of these mechanisms will prove invaluable when designing reversible networks in the future, making possible the precise control of their properties, thus fostering innovative applications within the food industry and beyond.

Food LEGO: Building hollow cage and sheet superstructures from starch.

The idea of building large structures from small building blocks has had a long history in the human imagination, from the beautifully intricate shells assembled from silica by unicellular algae to the Egyptian pyramids built from stone. Carrying this idea into the food industry has important implications. Here, we introduce a Pickering emulsion platform for building superstructures like hollow cages and sheets using starch granules as building blocks. In food, these superstructures occupy up to six times more space than their constituent parts, thereby delivering a viscosity greater by an order of magnitude than unstructured starch. To achieve this higher viscosity, they use an alternative superstructure mechanism as opposed to the classic swelling mechanism of individual particles. These super-thickeners may reduce calories, cut production costs, and stretch the global food supply, demonstrating how we can design the future by playing with our food.

Modulating Functionality of Starch-Based Patchy Particles by Manipulating Architecture and Environmental Factors.

Starch as a food-grade thickener has been commonly used in food products to modulate textural properties. Improving viscosity-enhancing ability, so as to be able to use less starch for the same texture, has been considered as an approach to reduce the dietary consumption of carbohydrates. We have positively charged amaranth starch (∼1 µm) and negatively charged corn starch (>10 µm) and physically fused the particles together to create a starch with a heterogeneous pattern. This starch has a negatively charged main body, due to the larger corn particles, and positively charged patches from the amaranth starch. These patchy particles self-assembled through electrostatic interactions into a shear-reversible thickener. The impact of patchiness and charge density on material functionality was investigated. The degree of patchiness was controlled by manipulating the ratio between the two starches, and results showed that viscosity was reduced when the patchiness was higher. With the same patchy area, a higher charge density did not contribute to higher water-holding capacity. The more charged particles were able to enhance the viscosity, however, due to the stronger interparticle electrostatic interaction. The effects of environmental factors including pH level and ionic strength were also investigated, and the results showed that at extreme pH levels, or in the presence of Na+ or Ca2+, the charges on the starch particles were screened, and this inhibited interaction and reduced viscosity. The present work demonstrates that the texture of starch slurries can be fine-tuned by manipulating the degree of patchiness and the charge density of patchy particles. It also evaluates the application potential in food products with different pH levels and ionic strengths.

Starch Janus Particles: Bulk Synthesis, Self-Assembly, Rheology, and Potential Food Applications.

Although incredible progress in the field of Janus particles over the last three decades has delivered many promising smart-material prototypes, from cancer-targeting drug delivery vehicles to self-motile nanobots, their real-world applications have been somewhat tempered by concerns over scalability and sustainability. In this study, we adapt a simple, scalable 3D mask method to synthesize Janus particles in bulk using starch as the base material: a natural biopolymer that is safe, biocompatible, biodegradable, cheap, widely available, and versatile. Using this method, starch granules are first embedded on a wax droplet such that half of the starch is covered; then, the uncovered half is treated with octenyl succinic anhydride, after which the wax coating is removed. Janus particles with 49% Janus balance can be produced in this way and were observed to self-assemble into wormlike strings in water due to their hydrophobic/hydrophilic nature. Our Janus starch granules outperform the non-Janus controls as thickening and gelling agents: they exhibit a fourfold increase in water-holding capacity, a 30% lower critical caking concentration, and a viscosity greater by orders of magnitude. They also form gels that are much firmer and more stable. Starch Janus particles with these functional properties can be used as novel, lower-calorie, highly efficient, plant-based super-thickeners in the food industry, potentially reducing starch use in food by 55%.

Fabrication of Charged Self-Assembling Patchy Particles Templated with Partially Gelatinized Starch.

Starch, as a staple carbohydrate, is frequently used as a thickener to enhance food texture. As such, there is an increasing interest in studying starch modification to improve its thickening ability. Instead of the conventional mechanism of swelling-based thickening, the present work presents an alternative using starch-based patchy particles as a texturizer prepared through a bottom-up method by physically grafting small amaranth starch granules (∼1 µm) onto corn starch granules (>10 µm). After thermal treatment in aqueous ethanol, starches were partially gelatinized, and the particle stiffness was reduced. The corn starch and amaranth starch were modified to carry a negative charge and a positive charge, respectively. The hydrated swollen starch granules were centrifuged and dehydrated, which stitched particles together, forming a corona-shaped patchy structure with a negatively charged core and positively charged patches. The electrostatic interaction allowed particles to associate, and the pockets created in the flocs were able to trap more water. The enhanced water-holding capacity consequently contributed to a significantly higher storage modulus, loss modulus, and viscosity compared to the native starch and the mixed charged starch with the same blending ratio between amaranth and corn starch. The enhanced viscoelasticity was not affected by cooking and mechanical stress, which could be used as a shear-reversible thickener to modify texture with less raw ingredients, thus helping to reduce the amount of energy-dense starch in diets. This is the first time that the concept of patchy particles has been extended to food-grade ingredients with a facile and scalable method.

Protein content of amaranth and quinoa starch plays a key role in their ability as Pickering emulsifiers.

Growing concerns about the safety of using synthetic surfactants to stabilize food emulsions have inspired a trend towards the use of natural ingredients like starch as alternative food stabilizers in what are called Pickering emulsions. The hydrophilicity of commercially available starches, however, necessitates further chemical treatment to increase their hydrophobicity and emulsifying ability. Here we demonstrate an alkaline isolation method to extract amaranth and quinoa starch from flour while retaining a high protein content, which gives these materials an emulsifying ability comparable to octenyl succinylated starches in the literature. We highlight the key role played by protein by showing that a serial reduction of the protein content leads to a parallel reduction in emulsifying ability, and that pH affects this ability. Our method of retaining proteins naturally present in amaranth and quinoa not only bolsters their nutritional profile but also takes advantage of these proteins' native hydrophobicity for improved emulsification.

Improvement of physicochemical properties of encapsulated echium oil using nanostructured lipid carriers.

Implementing ω-3 polyunsaturated fatty acids (ω-3 PUFA), naturally found in echium oil (EO), can highly improve the nutritional value of fortified foods. However, PUFA is prone to oxidation. In this study, the role of nanostructured lipid carriers incorporated into whey protein isolate (WPI)-stabilized EO droplets in oil-in-water emulsions was analyzed. Lipid carriers such as lauric (LA), palmitic (PA), and stearic (SA) acids were used. The results reveal that lipid carriers, especially LA, improve the physical stability of these droplets by decreasing their particle size by decreasing the number of surface pores; shown by SEM images and XRD data. Rheological data further show that the emulsions incorporated with LA had higher viscosity and there was also a crossover shift to lower strains in the G'-G″ curve of the emulsions incorporating LA. TBARS assay indicated that LA was more effective in protecting EO against oxidation than both palmitic and stearic acids.

Modulation of whey protein-kappa carrageenan hydrogel properties via enzymatic protein modification.

Treatment of whey protein isolate (WPI; 1 to 25% w/w) in heated κ-carrageenan (KC; 2% w/w) slurries with protease and/or transglutaminase modulated the properties of the hydrogels formed after cooling. Observation of peak compression stress and strain at gel rupture showed WPI incorporation at 1, 5 and 10% (w/w) significantly reduced the strength and deformability of 2% (w/w) KC gels. Treatment of WPI solutions in KC slurries with Alcalase 2.4L was shown by both SDS-Page and size exclusion HPLC to reduce protein/peptide molecular weight distributions below 10 kDa, with large portions below 1 kDa. This peptide size reduction within the KC matrix produced more translucent gels with a more organized wall and cell structure as observed by SEM, which resulted in gels with observed rupture stress/strain levels similar to 2% KC alone. Transglutaminase treatment of WPI-KC slurries showed the reverse behavior, reducing gel translucency, strength and deformability. At these loadings, WPI-KC gel strength/deformability appears to relate decreasing peptide size to gel behavior trending towards KC-only gels; suggesting peptide size modulation in protein-carbohydrate complexes will allow significant tailoring of texture for the delivery of protein/peptide rich gelled products.

Light-harvesting synthetic nano- and micromotors: a review.

Nano- and micromotors are machines that can be made to perform specialized tasks as they propel themselves in response to certain stimuli. While the design of these self-propelling nano- and micromotors remains challenging, they have nevertheless attracted considerable research due to their many promising applications. Most self-propelled nano- and micromotors are based on the conversion of chemical energy into mechanical movement. Recently, however, the development of motors that can be propelled by light as an external stimulus has received much attention. The reason being that light is a renewable energy source that does not require any physical connection to the motor, does not usually lead to any waste products, and is easy to control. This review highlights recent progress in the development of light-harvesting synthetic motors that can be efficiently propelled and accurately controlled by exposure to light, and gives an overview of their fabrication methods, propulsion mechanisms, and practical applications.

Nano- and micromotors for cleaning polluted waters: focused review on pollutant removal mechanisms.

Nano- and micromotors are machines designed to self-propel and-in the process of propelling themselves-perform specialized tasks like cleaning polluted waters. These motors offer distinct advantages over conventionally static decontamination methods, owing to their ability to move around and self-mix-which heightens the interaction between their active sites and target pollutants-thus improving their speed and efficiency, which could potentially decrease treatment times and costs. In the last decade, considerable research efforts have been expended on exploring various mechanisms by which these motors can self-propel and remove pollutants, proving that the removal of oil droplets, heavy metals, and organic compounds using these synthetic motors is possible. This review highlights recent progress in the design of these nano- and micromotors for cleaning polluted waters, and gives an overview of their structure, fabrication, and propulsion methods, with a special focus on the mechanisms by which they remove pollutants-namely, either by adsorption or by degradation. A fundamental understanding of these removal mechanisms, with their attendant advantages and disadvantages, can help researchers fine-tune motor design in the future so that technical issues can be resolved before they are scaled-up for a wide variety of environmental applications.