We here explore confinement-induced assembly of whey protein nanofibrils (PNFs) into microscale fibers using micro-focused synchrotron X-ray scattering. Solvent evaporation aligns the PNFs into anisotropic fibers and the process is followed in situ by scattering experiments in a droplet of PNF dispersion. We find an optimal temperature at which the order of the protein fiber has a maximum, suggesting that the degree of order results from a balance between the time scales of the forced alignment and the rotational diffusion of the fibrils. Moreover, we observe that the assembly process depends on the nano-scale morphology of the PNFs. Stiff PNFs with a persistence length in the micrometer scale are aligned at the air-water interface and the anisotropy gradually decrease towards the center of the droplet. Marangoni flows often increase entanglements toward the center, leading to complex patterns in the droplet. Flexible fibrils with a short persistence length (< 100 nm) tends to align uniformly throughout the droplet, possibly due to stronger local entanglements. Straight PNFs form smaller clusters with shorter inter-cluster distances due to their tight packing and consistent linear structure. In contrast, curved PNFs form intricate networks with larger characteristic distances and more varied structures because of their flexibility and adaptability.

Protein nanofibrils (PNFs), especially those from the whey protein β-lactoglobulin, hold the promise for applications in food technology, medicine, and sustainable materials. In this work, we explore the mechanisms underlying the sol-gel transition of whey protein isolate triggered by pre-fragmented whey fibrils (seeds) at low pH and high temperature. We show that, under these conditions, the formed hydrogels are constructed from PNFs. The presented results suggest that the seeds amplify the fibril growth process by providing active ends that capture peptide monomers produced via acid hydrolysis. This changes the fibrils' length distribution (up to 10-fold increase of their average contour length), and the samples reach the percolation threshold at a much lower mass concentration of fibrils. We also note that seeding has a strong impact on morphology and catalyzes a conversion of short, curved fibrils into long straight ones, which also contribute to the lower percolation limit. Rheological measurements indicate that attractive inter-fibrillar forces stabilize the PNF network. This is further evidenced by the gels’ resistance to disassembly across a wide pH range, implying that other forces than electrostatics are important for stabilizing the fibrillar network. Finally, we discuss the nature of the sol-gel transition based on continuum percolation theory, which corroborates the observed relationship between PNF length distribution and the sol-gel transition.

Access to efficient and affordable materials for water purification is of fundamental importance for the sustainable development of our society. Materials based on protein nanofibrils (PNFs) from agricultural waste- or side streams have recently been shown to have excellent adsorption properties for organic as well as inorganic pollutants. We here investigate the role of the nanostructure in aerogels made from whey protein isolate for the removal of a model pollutant (ibuprofen) from water. Water stable aerogels were produced using a recently developed approach for intrinsic crosslinking of protein materials without requiring additives. By comparing materials made from PNFs and from non-fibrillar whey protein we find that the fibrils have dual roles in enhancing the ibuprofen binding capacity. The PNFs do have a higher direct binding affinity but they also remodel the cell wall structures of the aerogels, resulting in a mesoporous network with enhanced ability of pollutant adsorption.

The major ampullate Spidroin 1 (MaSp1) is the main protein of the dragline spider silk. The C-terminal (CT) domain of MaSp1 is crucial for the self-assembly into fibers but the details of how it contributes to the fiber formation remain unsolved. Here we exploit the fact that the CT domain can form silk-like fibers by itself to gain knowledge about this transition. Structural investigations of fibers from recombinantly produced CT domain from E. australis MaSp1 reveal an α-helix to β-sheet transition upon fiber formation and highlight the helix No4 segment as most likely to initiate the structural conversion. This prediction is corroborated by the finding that a peptide corresponding to helix No4 has the ability of pH-induced conversion into β-sheets and self-assembly into nanofibrils. Our results provide structural information about the CT domain in fiber form and clues about its role in triggering the structural conversion of spidroins during fiber assembly.

Chiral and enantiopure perfluorinated sulfonimidamides act as low-molecular weight gelators at low critical gelation concentration (<1 mg mL-1) via supramolecular polymerization in nonpolar organic solvents and more heterogenic mixtures, such as biodiesel and oil. Freeze-drying of the organogel leads to ultralight aerogel with extremely low density (1 mg mL-1). The gelation is driven by hydrogen bonding resulting in a helical molecular ordering and unique fibre assemblies as confirmed by scanning electron microscopy, CD spectroscopy, and computational modeling of the supramolecular structure.

The deposition of proteins in the form of amyloid fibrils is closely associated with several serious diseases. The events that trigger the conversion from soluble functional proteins into insoluble amyloid are not fully understood. Many proteins that are not associated with disease can form amyloid with similar structural characteristics as the disease-associated fibrils, which highlights the potential risk of cross-seeding of disease amyloid by amyloid-like structures encountered in our surrounding. Of particular interest are common food proteins that can be transformed into amyloid under conditions similar to cooking. We here investigate cross-seeding of amyloid-beta (A beta), a peptide known to form amyloid during the development of Alzheimer's disease, by 16 types of amyloid fibrils derived from food proteins or peptides. Kinetic studies using thioflavin T fluorescence as output show that none of the investigated protein fibrils accelerates the aggregation of A beta. In at least two cases (hen egg lysozyme and oat protein isolate) we observe retardation of the aggregation, which appears to originate from interactions between the food protein seeds and A beta in aggregated form. The results support the view that food-derived amyloid is not a risk factor for development of A beta pathology and Alzheimer's disease.

Protein nanofibrils (PNFs) have potential for use in food applications as texture inducers. This study investigated the formation of PNFs from protein extracted from whole fava bean and from its two major storage proteins, globulin fractions 11S and 7S. PNFs were formed by heating (85 degrees C) the proteins under acidic conditions (pH 2) for 24 h. Thioflavin T fluorescence and atomic force microscopy techniques were used to investigate PNF formation. The foaming properties (capacity, stability, and half-life) were explored for non-fibrillated and fibrillated protein from fava bean, 11S, and 7S to investigate the texturing ability of PNFs at concentrations of 1 and 10 mg/mL and pH 7. The results showed that all three heat-incubated proteins (fava bean, 11S, and 7S) formed straight semi-flexible PNFs. Some differences in the capacity to form PNFs were observed between the two globulin fractions, with the smaller 7S protein being superior to 11S. The fibrillated protein from fava bean, 11S, and 7S generated more voluminous and more stable foams at 10 mg/mL than the corresponding non-fibrillated protein. However, this ability for fibrillated proteins to improve the foam properties seemed to be concentration-dependent, as at 1 mg/mL, the foams were less stable than those made from the non-fibrillated protein.

Protein nanofibrils (PNFs) have potential food uses due to their favorable mechanical and rheological properties. In order to use plant-based protein nanofibrils (PNFs) in new sustainable food applications, a better under-standing is needed of the impact of pH on PNFs and their functional properties. In this study, we developed an improved method for generating PNFs from mung bean protein isolate and its globular 8S fraction. We then investigated how these PNFs are affected by increased pH and how pH affects their ability to form stable foams. PNFs were generated in acidic conditions (pH 2) by heating at 85 degrees C for 2-48 h. Formation of PNFs and the effect of increased pH on their stability were evaluated using thioflavin T fluorescence, electrophoretic gel separation, circular dichroism spectroscopy, atomic force microscopy and viscosity profiling. Foams were made by intense mixing with a homogeniser and evaluated for foam capacity, foam stability and bubble size distribution, using confocal imaging. The results showed that it is possible to optimise the fibrillation conditions for mung bean by generating a more pure initial protein isolate by salt extraction. The results also showed that pH alters the structure of PNFs by degradation and aggregation around the isoelectric point of the protein isolate. At neutral pH, the PNFs were slightly shorter than at the starting pH, but no longer formed aggregates. Fibrillated mung bean protein at pH 4-8 was found to have good foaming properties compared with non-fibrillated protein at the same conditions. The new knowledge generated in this study about how pH alters the structure and foaming properties of PNFs can pave the way for use of PNFs in new innovative food applications.