Food transition requires the replacement in human diet of animal-based proteins by alternative sources of proteins including plant-based proteins. This calls for a detailed knowledge of the functional properties of plant-based proteins, including their surface activity. In this framework, we provide here a comparative study of the interfacial properties of two plant proteins, extracted respectively from wheat and sunflower. We combine time- and concentration-dependent measurements of the surface tension and the surface rheology, as measured with a pendant-drop set-up, and of the surface excess concentration, as measured by ellipsometry, of plant protein interfacial films. We demonstrate a time-concentration superposition principle for the surface pressure and surface excess concentration, showing that the kinetics for the building of the interfacial films is essentially governed by the diffusion of the proteins from the bulk to the interface. We find that the rheological and structural properties of the interfacial protein films show markedly different behaviors for the two classes of protein, which is encoded in the structural features of the individual proteins: wheat proteins are more surface active than sunflower proteins, are keen to compress and re-arrange at an air-water interface, whereas sunflower proteins do not. This work provides qualitative and quantitative analysis of the comparative interfacial behavior of flexible and rigid plant proteins extracted respectively from wheat and sunflower, and demonstrates that a combination of several experimental techniques is necessary to obtain insightful information on the interfacial properties of any species.

The adsorption of a sunflower protein extract at two air− water and oil−water interfaces is investigated using tensiometry, dilational viscoelasticity, and ellipsometry. For both interfaces, a three step mechanism was evidenced thanks to master curve representations of the data taken at different aging times and protein concentrations. At short times, a diffusion limited adsorption of proteins at interfaces is demonstrated. First, a two-dimensional protein film is formed with a partition of the polypeptide chains in the two phases that depends strongly on the nature of the hydrophobic phase: most of the film is in the aqueous phase at the air−water interface, while it is mostly in the organic phase at the oil−water interface. Then a three-dimensional saturated monolayer of proteins is formed. At short times, adsorption mechanisms are analogous to those found with typical globular proteins, while strong divergences are observed at longer adsorption times. Following the saturation step, a thick layer expands in the aqueous phase and appears associated with the release of large objects in the bulk. The kinetic evolution of this second layer is compatible with a diffusion limited adsorption of the minor population of polymeric complexes with hydrodynamic radius R H ∼ 80 nm, evidenced in equilibrium with hexameric globulins (R H ∼ 6 nm) in solution. These complexes could result from the presence of residual polyphenols in the extract and raise the question of the role of these compounds in the interfacial properties of plant protein extracts.

Cinnamic acid and acetosyringone recrystallize in vegetable oil as platelets and rods respectively. After dissolution at high temperature(100°C) and upon cooling down to room temperature, their crystallites aggregate into a tenuous network which spans the entire volume of the system even at low mass fraction such as 1%. The whole system behaves as a soft solid characterized by an elastic modulus reaching 1MPa for mass fraction below 10% in the linear regime. The elastic modulus of cinnamic acid based oleogels varies with mass fraction as (-0) 2. For acetosyringone based oleogels, the elastic modulus varies non monotonically with concentration. This has been correlated to a morphological crossover from jammed spherulites at low mass fraction to entangled rods at higher mass fraction. Spherulite formation is related to the presence of branching points along the rods that result from secondary nucleation events. A new empirical parameter is defined from rheological data which reflects how far from equilibrium the solidification proceeds in nonisothermal conditions. This parameter accounts for the different concentration regimes of morphology and rheological properties that have been observed experimentally for acetosyringone.

Self-assembling peptides (SAPs) have been extensively studied for their ability to form nanoscale ordered structures driven by noncovalent molecular interactions. Meanwhile, polymerization-induced self-assembly (PISA) has been exploited as a facile and efficient way to produce various amphiphilic block copolymer nano-objects, whose self-assembly was governed predominantly by the interactions of the different blocks with the polymerization medium. In this work, we combined PISA with SAPs to prepare novel peptide–polymer hybrid nano-objects, thus harnessing the advantages of PISA and the self-assembling driving force of SAPs. A tripeptide methacrylamide derivative (MAm-Gly-Phe-Phe-NH2, denoted as MAm-GFF, where MAm means methacrylamide) was copolymerized with glycerol monomethacrylate (GMA) to produce a P(GMA65-stat-(MAm-GFF)7) macro-chain transfer agent (macro-CTA) by reversible addition–fragmentation chain transfer polymerization in dimethylformamide. This peptide-based macro-CTA was then successfully chain-extended with poly(2-hydroxypropyl methacrylate) (PHPMA) by aqueous dispersion PISA, forming P(GMA65-stat-(MAm-GFF)7)-b-PHPMA28 self-assembled objects. Fibrous structures were observed by transmission electron microscopy (TEM) and Cryo-TEM, in agreement with depolarized dynamic light scattering, static light scattering, and small-angle X-ray scattering experiments that also revealed long anisotropic morphologies. Such structures have not been reported previously for PISA-prepared nano-objects. This confirms the decisive influence of the GFF SAP on the self-assembly. In addition, annealing the PISA suspension at different temperatures led to a significant size decrease in the self-assembled objects and to a morphological transition caused by the thermosensitivity of both the core-forming PHPMA block and the stabilizing P(GMA-stat-(MAm-GFF)) block.

Well-defined double hydrophilic block copolymers (DHBCs) of poly(ethylene glycol)-block-poly(N,N-diethyla-crylamide) (PEG-b-PDEAm) were synthesized via a reversible addition-fragmentation chain-transfer (RAFT) polymerization of N,N-diethylacrylamide (DEAm) using dithioester terminated PEG of different chain lengths as macro-chain transfer agents. Controlled molecular weight and narrow molecular weight distribution were achieved as proven by size exclusion chromatography (SEC). Cloud points (CP) were determined via turbidity measurements with ultraviolet-visible spectroscopy (UV-vis) and LCST by differential scanning micro-calori-metry (micro-DSC). They range from 32 to 40°C depending on the PDEAm length block and its concentration. Above the LCST, fluorescence spectroscopy and dynamic light scattering (DLS) demonstrated that the PEG-b-PDEAm copolymers self-organized into large aggregates. More interestingly, copolymers pre-aggregated at relatively high concentrations below the LCST.

Free solution capillary-electrophoresis (CE) is a powerful separation technique for the characterization of diblock copolymers. In this work, four series of double-hydrophilic anionic and cationic block copolymers, namely, poly(acrylamide)-block-poly(acrylic acid) (PAM-b-PAA), poly(acrylamide)-block-poly((3-acrylamidopropyl)trimethylammonium chloride) (PAM-b-PAPTAC), poly(ethylene oxide)-block-poly(acrylic acid) (PEO-b-PAA) and poly(poly(ethylene glycol) methyl ether acrylate)-block-poly(acrylic acid) (P(PEGA)-b-PAA), were synthesized by reversible additionfragmentation chain transfer (RAFT) polymerization and characterized by CE. The electrophoretic mobility distributions of the copolymers were transformed into distributions of composition ratio by introducing a retardation parameter, Xexp,, that represents the hydrodynamic drag retardation due to the neutral block of the copolymer. A linear correlation between Xexp and the ratio of the degrees of polymerization of each blocks was experimentally established and was consistent with the model of electrophoretic mobility of composite macromolecules with hydrodynamic coupling. Finally, the comparison of the distributions between the different copolymer families was significantly improved by considering the distributions in composition ratio compared to the electrophoretic mobility distributions, since it takes into account the differences in solvation, expansion and drag force according to the chemical nature of the blocks.