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Protein-based microfibers have potential applications in bioengineering and food but preserving and utilizing the unique nanomechanical properties of their protein building blocks at the micrometer scale remains a challenge. This study investigates the bottom-up fabrication of core-shell fibers by coaxial microfluidic spinning of pectin and β-lactoglobulin in different conformational states (monomeric, amyloid fibrils, shortened amyloid fibrils in their isotropic/nematic phases), gelled in CaCl2 solution. Fiber diameters ranged between 478 and 855 μm (wet state) and 107–135 μm (dry state). They showed clear core-shell cross-sections, except pectin-β-lactoglobulin monomer fibers where the compact protein is presumably understood to diffuse through the pectin matrix. The molecular orientation of the fiber building blocks was expressed as order parameters representing the alignment of pectin chains and amyloid fibrils parallel to the fiber axis calculated from synchrotron wide-angle X-ray scattering (WAXS) with a spatial resolution of 20 μm. Introduction of amyloid fibrils as the protein core increased the Young's modulus from 3.3 to 6.4 GPa and tensile strength from 117 to 182 MPa compared to pure pectin fibers. Increasing the protein core flow rate from 1 to 2 mL/h, however, caused helical bending of the core jet, a decrease in order, and ultimately worsened mechanical performance. Overall, full length amyloid fibrils proved to be more beneficial to the mechanical properties than shortened amyloid fibrils. By providing insight into the relationship between protein conformation, spinning flow rate, and resulting mechanical properties of core-shell microfibers, these results may contribute to the field of novel fibrous protein-based materials., Food Hydrocolloids, 143, ISSN:0268-005X, ISSN:1873-7137

Amyloid fibrils from plant-based food protein sources bear a large unexploited potential for applications in food and other biomaterials due to their techno-functional features. However, their low solubility and highly complex, inhomogeneous protein composition often hamper fibrillization. The objective of this study was to evaluate the feasibility of amyloid fibril production from hemp seed protein, known as a sustainable and low-allergenic protein source. Hemp protein concentrate (HPC), primarily constituted of the 11 S globulin edestin, with 89.0% protein solubility (0.25% w/w HPC, pH 2) was extracted using gentle micellization. Fibrillization of HPC (2% w/w, pH 2, 90 °C, 300 rpm) was monitored over 5 h by ThT fluorescence, exhibiting a steep increase in fluorescence signal after a lag phase of 180 min. SDS-PAGE analysis indicated progressive polypeptide hydrolysis upon heating and the formation of large proteinaceous aggregates after 160 min. Conformational changes towards increased β-sheet content were demonstrated by CD and FTIR. The morphology of the formed fibrillar aggregates was characterized by TEM and AFM. While essentially linear, branching effects of the fibrils became visible and kept increasing with incubation time. After a relatively short incubation time of 4 h, fibrils had an average height of 7.8 nm, a contour length of 1.8 μm, and a persistence length of ∼2.7 μm. These results suggest, that under the chosen conditions for protein extraction and incubation, HPC forms relatively flexible amyloid fibrils with a high aspect ratio and tendency to form branches. By revealing the potential of hemp seed proteins for amyloid fibril formation, these results contribute to expand the understanding of plant protein fibrillization., Food Hydrocolloids, 137, ISSN:0268-005X, ISSN:1873-7137

Artificial functional materials based on amyloid fibrils are proven to be a promising strategy toward functional materials. However, scaling-up applications present sustainability concerns, as animal proteins are the main sources for fabricating amyloid fibrils. Plant-protein-based amyloid fibrils, a more sustainable alternative to animal proteins, are attracting increasing interests as building blocks in functional materials. Herein, 11 different sources from a wide range of plants are evaluated, and a comprehensive analysis of seven species of plant proteins, including kidney bean, black bean, cowpea, mung bean, chickpea, lentil, and pumpkin seed, with an excellent ability to form fibrils, is presented. A universal strategy for a diversity of plant protein extraction and fibrillization is applied. Flexible fibrils with a persistence length of approximate to 100 nm and rigid fibrils of several micrometers are discovered in 7S/8S and 11S subunits dominated protein, respectively. Structural evolution toward the beta-sheet content on these proteinaceous assemblies is characterized by thioflavin T (ThT) intensity, circular dichroism (CD) spectra, attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectra, and typical wide angle X-ray scattering (WAXS) spectra. Finally, their multifunctional applications are further explored and proven that these sustainable protein amyloids demonstrate excellent performance in renewable and degradable bioplastics, and in water purification membranes for heavy metal removal., Advanced Sustainable Systems, 7 (4)

If safety concerns could be conclusively disproven, food protein amyloid fibrils would constitute superior ingredients compared to native monomers from a technological, nutritional, sensorial, and physical perspective. Here, we show, by combining SDS-PAGE, ELISA, fluorescence, AFM, TEM, MALDI-MS, CD, microfluidics, and SAXS techniques on β-lactoglobulin and lysozyme amyloid fibrils subjected to in-vitro gastrointestinal digestion, that either no noticeable differences exist between amyloid aggregates and their monomer counterparts after the gastrointestinal digestion process (as in β-lactoglobulin), or that amyloid fibrils are even digested significantly better than monomers (as in lysozyme). Both amyloid protein sources are digested down to unfolded oligopeptides well-below amyloid nuclei size and deprived of the β-sheet amyloids hallmark signature. We further conclude via in-vivo studies on both C. elegans and mice animal models that the digested fibrils present no observable toxicity to the investigated animal models. These results suggest that final peptides digested from food amyloids fibrils are at least equally safe than those obtained from the digested corresponding native monomers and feature no detectable toxicity in-vivo, pointing to food amyloid fibrils as potential ingredients for human nutrition.

Nanofiber mats can be produced by electrospinning from diverse polymers and polymer blends as well as with embedded ceramics, metals, etc. The large surface-to-volume ratio makes such nanofiber mats a well-suited substrate for tissue engineering and other cell growth experiments. Cell growth, however, is not only influenced by the substrate morphology, but also by the sterilization process applied before the experiment as well as by the chemical composition of the fibers. A former study showed that cell growth and adhesion are supported by polyacrylonitrile/gelatin nanofiber mats, while both factors are strongly reduced on pure polyacrylonitrile (PAN) nanofibers. Here we report on the influence of different PAN blends on cell growth and adhesion. Our study shows that adding ZnO to the PAN spinning solution impedes cell growth, while addition of maltodextrin/pea protein or casein/gelatin supports cell growth and adhesion.

Compared to commonly applied wet and dry heating procedures, a combination of electrospinning and heat treatment can facilitate glycation of proteins with reducing polysaccharides. This study investigates how the amount of reducing carbonyl groups (i.e. dextrose equivalent, DE) of different maltodextrins influences electrospinnability and subsequent glycation in blends with pea protein isolate (PPI). In the first step of the study, maltodextrin-PPI dispersions were electrospun. The concentrations of PPI and maltodextrin DE 2 were kept constant in the aqueous spinning dispersion. The addition of 0.05 or 0.1 g/mL maltodextrin DE 12 or 21 slightly affected the electrical conductivity and dynamic viscosity of the spinning dispersions, however, fiber production rate and morphology were dominated by the presence of maltodextrin DE 2 (0.8 g/mL). In the second step of the study, fibers were heated (60 °C, 75% rel. Humidity, 0–24 h). SDS-PAGE analysis and the measurement of free amino groups confirmed the covalent attachment of maltodextrin carbonyl groups to free amino groups of PPI. The fastest glycation and the lowest relative amount of free amino groups (49.70 ± 6.54%) after 24 h heating was measured for the fibers with the highest amount of reducing carbonyl groups. The fibers with the lowest amount of reducing carbonyl groups showed no significant (p

The production of food-grade fibers from maltodextrin with either whey protein isolate or soy protein isolate was evaluated in a needleless electrospinning setup. The ratio of maltodextrin to protein was varied. Higher protein content generally led to a higher electrical conductivity and viscosity. Compared to WPI samples, the use of SPI decreased the surface tension of the spinning dispersions while at the same time increasing the electrical conductivity from 0.39 ± 0.00 mS/cm (WPI 80:5) to 0.64 ± 0.01 mS/cm (SPI 80:5) and the apparent viscosity ( γ ˙ = 100 s−1) from 4.58 ± 0.14 Pa⋅s (WPI 80:5) to 5.14 ± 0.09 Pa⋅s (SPI 80:5). The high viscosity was identified to hinder electrospinning and the maltodextrin-SPI fibers had lower production rates of 0.50 ± 0.25 g/h (SPI 80:5) and higher diameters 4.74 ± 2.33 μm (SPI 80:5) compared to maltodextrin-WPI fibers (0.98 ± 0.13 g/h and 2.85 ± 0.95 μm for WPI 80:5). Removing the insoluble fraction of the SPI and only using the soluble soy protein (SSPI) with maltodextrin for electrospinning resulted in a lower viscosity (4.63 ± 0.05 Pa⋅s for SSPI 80:5) and better spinning results (0.5 g/h ± 0.06). FTIR analysis and protein measurement showed that the resulting fibers consisted of both the maltodextrin and the proteins. The protein content in the fibers was thereby linked to the spinnability and fiber appearance.

A high foam stability (FS) is important for manufacturers and is mainly achieved through high protein concentrations. Consequently, the increase of FS at lower protein concentrations is desirable f...

Plant proteins are being considered to become the most important protein source of the future, and to do so, they must be able to replace the animal-derived proteins currently in use as techno-functional food ingredients. This poses challenges because plant proteins are oftentimes storage proteins with a high molecular weight and low water solubility. One promising approach to overcome these limitations is the glycation of plant proteins. The covalent bonding between the proteins and different carbohydrates created via the initial stage of the Maillard reaction can improve the techno-functional characteristics of these proteins without the involvement of potentially toxic chemicals. However, compared to studies with animal-derived proteins, glycation studies on plant proteins are currently still underrepresented in literature. This review provides an overview of the existing studies on the glycation of the major groups of plant proteins with different carbohydrates using different preparation methods. Emphasis is put on the reaction conditions used for glycation as well as the modifications to physicochemical properties and techno-functionality. Different applications of these glycated plant proteins in emulsions, foams, films, and encapsulation systems are introduced. Another focus lies on the reaction chemistry of the Maillard reaction and ways to harness it for controlled glycation and to limit the formation of undesired advanced glycation products. Finally, challenges related to the controlled glycation of plant proteins to improve their properties are discussed., Foods, 10 (2), ISSN:2304-8158

Heat-treated electrospun pea protein isolate (PPI)–maltodextrin fibers containing glycated PPI were analyzed for their interfacial tension and emulsifying properties compared to unheated electrospun PPI–maltodextrin fibers. Interfacial tension at the oil–water-interface of the heated fibers was higher (19.2 ± 0.1 mN m−1) compared to the unheated fibers (16.3 ± 1.4 mN m−1) due to the covalently bound hydrophilic maltodextrin in the glycoconjugates. Applied in oil-in-water emulsions (10% w/w oil, 0.7% protein, 103.4 MPa, 3 passes), unheated PPI–maltodextrin fibers produced large droplets (72–259 μm) with multimodal distributions in the pH range of 2–7. The largest droplet size was at pH 4, which was around the pI of PPI. Emulsions were also prone to flocculation, which was most probably caused by a depletion flocculation mechanism due to an excess of maltodextrin in the aqueous phase. In contrast, emulsions made with heated PPI–maltodextrin fibers were monomodal (36–55 μm) at pH 2–7 and only showed a minor increase in droplet size close to the pI of PPI. The improved properties of heated PPI–maltodextrin fibers were ascribed to the enhanced steric repulsion caused by the covalently bound maltodextrin. The results indicate that Maillard-induced glycation of PPI with maltodextrin in electrospun fibers can be used as a novel method to improve the properties of PPI as a plant-based emulsifier.

Glycation of proteins via the first stage of the Maillard reaction is capable of improving their stability but not economically feasible yet. This work reports the glycation of whey protein isolate (WPI) with maltodextrin at a high yield after heating electrospun fibers made from the reactants. Glycoconjugates were characterized by Fourier transform infrared spectroscopy (FTIR) and SDS-PAGE. The binding ratio between WPI and maltodextrin was assessed via the free amino groups. The molecular weight of the conjugates and the reaction yield were studied by size exclusion chromatography. The impact of different mass ratios between WPI and maltodextrin in the fibers (5:95, 10:90, 20:80, and 25:75 w/w) was investigated. With increasing WPI content, the binding ratio of maltodextrin decreased from ∼2.1 to ∼1.2. Preferably small polysaccharides (2-13 kDa) from the maltodextrin reacted. Protein specific reaction yields of up to 44.52 ± 7.46% w/w were demonstrated in all WPI-maltodextrin fibers after heating.

A secreted peptidase from Pseudomonas panacis was identified and purified. Genome sequencing of the producer strain allowed identification of the peptidase as AprA based on a comparison to peptide sequences of mass spectra obtained from the purified enzyme. The amino acid sequence of the 49.4 kDa peptidase was 98% similar to the metallopeptidase AprX from a Pseudomonas fluorescens strain. The peptidase showed maximum activity at pH 8 and 40 °C and withstood general ultra-high temperature (UHT) processing (138 °C for 18 s) in skim milk, with 88.0 ± 7.7% of the initial enzyme activity remaining after heating. The peptidase showed considerable enzyme activity under storage conditions of UHT milk. The potential for spoilage of milk might during storage was verified by adding very low enzyme activities to UHT-treated milk. The addition of 1 pkat mL −1 peptidase activity resulted in a destabilisation of the milk during four weeks storage.