A clickable, highly soluble oligopeptide that easily forms organogels

Preparation of Protein Oleogels: Effect on Structure and Functionality

Among available structuring agents that have been used to provide solid properties to liquid oils, protein is a more recent candidate. Due to their nutritional value and high consumer acceptance, proteins are of special interest for the preparation of edible oleogels as an alternative for solid fats. Whereas the field of protein oleogelation is still rather new and just starts unfolding, several preparation methods have been demonstrated to be suitable for protein oleogel preparation. However, there is limited knowledge regarding the link between microstructural properties of the gels and macroscopic rheological properties, and the potential of such protein-based oleogels as a fat replacer in food products. In this review, we therefore provide an overview of various protein oleogel preparation methods and the resulting gel microstructures. Based on the different structures, we discuss how the rheological properties can be modified for the different types of protein oleogels. Finally, we consider the suitability of the different preparation methods regarding potential applications on industrial scale, and provide a short summary of the current state of knowledge regarding the behavior of protein oleogels as a fat replacer in food products.

A Peptide Amphiphile Organogelator of Polar Organic Solvents

A peptide amphiphile is reported, that gelates a range of polar organic solvents including acetonitrile/water, N,N-dimethylformamide and acetone, in a process dictated by β-sheet interactions and facilitated by the presence of an alkyl chain. Similarities with previously reported peptide amphiphile hydrogelators indicate analogous underlying mechanisms of gelation and structure-property relationships, suggesting that peptide amphiphile organogel design may be predictably based on hydrogel precedents.

Protein oleogels from heat-set whey protein aggregates

In this research we use heat-set whey protein aggregates (diameter∼200nm) as novel building blocks for structure formation in liquid oil to form oleogels. To transfer the aggregates to the oil phase, a solvent exchange procedure to sunflower oil was applied using acetone as an intermediate solvent. We found that agglomeration of the aggregates was prevented and the particle size in oil did not change from that in the initial aqueous phase. The small protein aggregates assemble into a space-spanning network, thereby providing solid-like properties to liquid oil. From oscillatory rheology we conclude that the aggregates are highly effective in forming a network. Already at ∼3% we found that G'>G″ and G' scales with protein concentration as G'∼c_p^5.3. Applying a fractal gel network theory to the rheological data we deduce that the gels are in the strong link regime with a fractal dimension of 2.2. The results show that protein aggregates, besides their well-known functionality in aqueous solvents, are capable of forming a network in liquid oil. This provides a novel and promising way to design oleogels with tuneable rheological properties, applicable to e.g. foods, pharmaceuticals and/or cosmetics.

Protein Oleogels from Protein Hydrogels via a Stepwise Solvent Exchange Route

We investigated the use of whey protein isolate (WPI) as oleogelator in liquid oil. First, heat-set WPI hydrogels were prepared varying in microstructure and network density. Then, by applying a stepwise solvent exchange procedure via an intermediate solvent, full replacement of the internal aqueous phase within the protein matrix by sunflower oil was achieved. The solvent exchange procedure was performed by using either acetone or tetrahydrofuran (THF) as intermediate solvent. The oil inside the protein matrix was homogeneously distributed without any noticeable damage to the structure. Analyzing the weight change of the protein gel as a result of the solvent exchange shows that the oil holding capacity depends on the microstructure, the polarity of the intermediate solvent, and the kinetics of the solvent exchange. Depending on the gel microstructure and protein concentration of the preceding hydrogel, the oil content in the oleogels was found to be as high as 91 wt %. Oil holding capacity correlated well with the water holding capacity of the preceding hydrogel, and its Young's modulus (stiffness). It was found that the oleogels, compared to the hydrogels, were much stiffer, as the Young's modulus increased by 2 orders of magnitude and showed a lower strain at fracture. Our novel route of structuring oil by immobilizing liquid oil inside a biodegradable protein gel matrix with tunable mechanical properties could be relevant for developing novel materials, e.g., in pharmaceutical, nutraceutical, and food applications.

Inclusion of Cu nano-cluster 1D arrays inside a C3-symmetric artificial oligopeptide via co-assembly

A peptide sequence N(3)-GVGV-OMe (G: glycine; V: valine) was attached to a benzene 1,3,5-tricarboxamide (BTA) derivative via"click chemistry" to afford a C(3)-symmetric artificial oligopeptide. The key feature of this oligopeptide is that the binding sites (triazole groups formed by click reaction) are located at the center, while the three oligopeptide arms with a strong tendency to assemble are located around it, which provides inner space to accommodate nanoparticles via self-assembly. The inclusion of Cu nanoclusters and the formation of one-dimensional (1D) arrays inside the nanofibers of the C(3)-symmetric artificial oligopeptide assembly were observed, which is quite different from the commonly observed nanoparticle growth on the surface of the pre-assembled oligopeptide nanofibers via the coordination sites located outside. Our finding provides an instructive concept for the design of other stable organic-inorganic hybrid 1D arrays with the inorganic nanoparticles inside.

Tetrapeptide-coumarin conjugate 3D networks based on hydrogen-bonded charge transfer complexes: gel formation and dye release

Oligopeptide-based derivatives are important synthons for bio-based functional materials. In this article, a Gly-(L-Val)-Gly-(L-Val)-coumarin (GVGV-Cou) conjugate was synthesized, which forms 3D networks in ethanol. The gel nanostructures were characterized by UV-vis spectroscopy, FT-IR spectroscopy, X-ray diffraction (XRD), SEM and TEM. It is suggested that the formation of charge transfer (CT) complexes between the coumarin moieties is the main driving force for the gel formation. The capability of the gel to encapsulate and release dyes was explored. Both Congo Red (CR) and Methylene Blue (MB) can be trapped in the CT gel matrix and released over time. The present gel might be used as a functional soft material for guest encapsulation and release.

Polymer organogelation with chitin and chitin nanocrystals

In this paper, we show that biodegradable and biocompatible organogels can be formed with chitin as the filler material and triglycerides as the continuous hydrophobic phase.

Tunable Organogelator from Alkyl-Polypeptide Diblock Prepared by Ring-Opening Polymerization

Three alkyl-polypeptide hybrid amphiphiles were synthesized by the ring-opening polymerization (ROP) of γ-(2-methoxyethoxy)esteryl-l-glutamate N-carboxyanhydride (l-EG1Glu NCA) using alkylamine, i.e. C6H13NH2, C14H29NH2, and C16H33NH2, as initiators. As-prepared alkyl-poly-l-EG1Glu hybrids were found to form clear organogels in several organic solvents at low concentration. FTIR and circular dichroism characterizations suggested that poly-l-EG1Glu formed a predominantly β-sheet conformation, which accounted for the gelation. Transmission electron and atomic force microscopy characterizations revealed that these copolymers formed nanoribbon structures in THF.