Heat-induced fibril assembly of vicilin at pH2.0: Reaction kinetics, influence of ionic strength and protein concentration, and molecular mechanism

Fibrillization of lentil proteins is impacted by the protein extraction conditions and co-extracted phenolics

Legume proteins can be induced to form amyloid-like fibrils upon heating at low pH, with the exact conditions greatly impacting the fibril characteristics. The protein extraction method may also impact the resulting fibrils, although this effect has not been carefully examined. Here, the fibrillization of lentil protein prepared using various extraction methods and the corresponding fibril morphology were characterized. It was found that an acidic, rather than alkaline, protein extraction method was better suited for producing homogeneous, long, and straight fibrils from lentil proteins. During alkaline extraction, co-extracted phenolic compounds bound proteins through covalent and non-covalent interactions, contributing to the formation of heterogeneous, curly, and tangled fibrils. Recombination of isolated phenolics and proteins (from acidic extracts) at alkaline pH resulted in a distinct morphology, implicating a role for polyphenol oxidase also in modifying proteins during alkaline extraction. These results help disentangle the complex factors affecting legume protein fibrillization.

Upcycling of Defatted Sesame Seed Meal via Protein Amyloid-Based Nanostructures: Preparation, Characterization, and Functional and Antioxidant Attributes

Herein, the possibility of valorizing defatted sesame seed meal (DSSM) as a viable source for valuable plant proteins and amyloid-based nanostructure was investigated. Sesame seed protein isolate (SSPI) and the major storage protein globulin (SSG) were prepared by alkaline extraction-isoelectric point precipitation as well as fractionation in the case of SSG. The protein samples were characterized for their physicochemical attributes. SSPI and SSG were also evaluated for their ability to form amyloid structures under heating (90 °C) at low pH (2.0). Additionally, the functional attributes, antioxidant activity, and biocompatibility of the proteins and amyloid nanostructures were also examined. SSPI and SSG were both successfully prepared from DSSM. The data showed that the physicochemical attributes of both protein samples were quite similar, except for the fact that SSG was mostly composed of 11S globulin, as evinced by Tricine-SDS-PAGE analysis. TEM micrographs revealed that SSG was able to form curly-shaped fibrillar amyloid structures, whereas those derived from SSPI were mostly amorphous. Thioflavin-T assay and Tricine-SDS-PAGE analysis indicated that acidic heating promoted protein hydrolysis and self-aggregation of the hydrolyzed peptides into a β-sheet rich amyloid structure. Importantly, the amyloid preparations displayed commendable solubility, superior water and oil holding capacities, and antioxidant activity against DPPH and ABTS. The protein amyloid nanostructures were found to be non-toxic against RAW264.7 cells, HaCaT cells, and red blood cells. These findings indicate that DSSM could be upcycled into valuable protein amyloid structures with good potentialities as novel food ingredients.

Fabrication of bovine serum albumin nanofibrils: Physicochemical characteristics, emulsifying and foaming activities

Bovine serum albumin nanofibrils (BSNs) were fabricated under thermal treatment (85 °C) at acidic condition (pH 2.0) and the incubation time on the structural, and physicochemical characteristics were probed. The formation and development of BSNs have been detected and confirmed by Thioflavin T (ThT) fluorescence and circular dichroism (CD) measurements. The structural alterations of bovine serum albumin (BSA) have also been investigated using intrinsic fluorescence and Congo red (CGR) UV-vis spectroscopy. Atomic force microscopy (AFM) outcomes displayed the morphologies of BSNs at varied time, with a diameter of about 3 nm and a contour length of about 200 nm at 24 h. The apparent viscosities of BSNs at three different pH were in the following order: pH 3.0 > pH 5.0 > pH 7.0. Emulsifying and foaming properties of BSA were pronouncedly enhanced through fibrillation, which was highly correlated with the interfacial properties and structural characteristics. Highest EAI 54.2 m2/g was attained at 48 h and no pronounced alterations were observed for EAI at 24 h and 48 h. Maximum value of FC was obtained at 48 h for BSA. This study will provide some useful information in understanding the formation of BSNs and broaden their application in food systems as functional food ingredients.

Specific ions effect on aggregation behaviors and structural changes of amyloid fibrils from rice glutelin

Metal ions have been considered as an important factor on fibrils assembly. Herein, a comprehensive analysis of specific ions effect on fibril formation and structural changes was investigated. The addition of ions (except Zn2+) accelerated the aggregation kinetics of rice glutelin fibrils (RGFs) from 0.93 to 1.28-2.19 h-1. In addition, the fibrillization rate followed the order of NH4+ > Li+ > Na+ > K+ > Cu2+ > Mg2+ > Ca2+ > Zn2+. The highest yield and length of fibrils were observed with Ca2+, probably due to the ionic bridging effect and hydrated capacity of Ca2+. However, Cu2+ reduced the fibrils yield, which was attributable to the fact that Cu2+ disrupted β-sheet structure and inhibited the transition of monomer to fibrils. The polymorphism of fibrils was observed with different salts, and the light metals presented a superior effect on fibrils formation than heavy metals. Overall, this work will provide a further information into how to tune the structure of RGFs using various ions.

Proteolysis improves the foaming properties of rice protein fibrils: Structure, physicochemical properties changes, and application in angel food cake

Proteolysis prior to fibrillation can change the functional properties of protein fibrils. This study aimed to investigate the effects of proteolysis pretreatment by alkaline protease on formation, structure, and foaming properties of rice protein fibrils. Thioflavin T fluorescence and conversion assays showed that proteolysis reduced the fibril formation capacity of rice protein. After 12 h of heating, the percent conversion of rice protein and rice protein hydrolysates to fibrils reached 60.32 ± 1.07% and 30.43 ± 2.01%, respectively. Transmission electron microscopy images showed that fibrils derived from rice protein hydrolysates had a longer contour length than rice protein fibrils. The foaming capacity and stability of rice protein hydrolysate fibrils increased by 16.70% and 11.27%, respectively, compared with those of rice protein fibrils. The addition of rice protein hydrolysate fibrils improved the texture of cakes. These results suggested that rice protein hydrolysate fibrils could be a promising plant-based foaming agent.

Salt-Promoted Fibrillation of Legume Proteins Enhanced Interfacial Modulus for Stabilization of HIPEs Encapsulating Carotenoids with Improved Nutritional Performance

The thermal acidic-treatment-induced fibrillation of legume proteins isolated from cowpea and mung bean was demonstrated to be promoted by salt. Worm-like thin prefibrilar intermediates were formed in low salt concentrations (0-75 mM), which twisted to be the thick and mature amyloid-like fibrils with multistrands as the salt content was elevated (150-300 mM). Absorption of the fibrils fabricated in high salt concentrations to the oil/water interface constructed the protein layer with a significantly higher interfacial modulus compared with the one formed by the fibrils fabricated in low salt concentrations. Consequently, they showed the superiority in stabilizing high internal phase emulsions (HIPEs) with oil volume fraction ratios higher than 74%. HIPEs stabilized by the high salt-concentration-induced legume protein fibrils had stronger capabilities not only in encapsulating liposoluble carotenoids but also in protecting their stability against heating, ultraviolet, and iron ion stimulus, compared with the one stabilized by the low-salt-concentration-induced legume protein fibrils. Bioaccessibilities of the carotenoids in simulating gastrointestinal (GI) digestion were significantly improved after encapsulation by the HIPEs, which were interestingly increased with the elevation of salt concentrations utilized for preparing the legume protein fibrils. Furthermore, the carotenoids-loading-HIPEs were injectable and showed in vivo nutritional functions of mitigating colitis.

Fibrillation modification to improve the viscosity, emulsifying, and foaming properties of rice protein

Fibrillation of food proteins has attracted considerable attention as it can improve and broaden the functionality of proteins. In this study, we prepared three kinds of rice protein (RP) fibrils with different structural characteristics by the regulation of NaCl and explored the effect of protein structure on viscosity, emulsifying, and foaming properties. AFM results showed fibrils formed at 0 and 100 mM NaCl were mainly in the range of 50-150 nm and 150-250 nm, respectively. Fibrils formed at 200 mM NaCl were in the range of 50-500 nm and protein fibrils longer than 500 nm increased. There was no significant difference between their height and periodicity. Fibrils formed at 0 and 100 mM NaCl were more flexible and unordered than those formed at 200 mM NaCl. The viscosity consistency index K of native RP and fibrils formed at 0, 100, and 200 mM NaCl were determined. The K value of fibrils was higher than that of native RP. The emulsifying activity index, foam capacity and foam stability were enhanced by fibrillation, while longer fibrils exhibited lower emulsifying stability index, which may be because long fibrils resulted in difficulty of cover of emulsion droplets. In summary, our work provided a valuable reference for improving the functionality of rice protein and facilitated the development of protein-based foaming agents, thickeners, and emulsifiers.

Morphology, Formation Kinetics and Core Composition of Pea and Soy 7S and 11S Globulin Amyloid Fibrils

Legume seed storage proteins can be induced to form amyloid fibrils upon heating at low pH, which could improve their functionality for use in food and materials. However, the amyloidogenic regions of legume proteins are largely unknown. Here, we used LC-MS/MS to determine the amyloid core regions of fibrils formed by enriched pea and soy 7S and 11S globulins at pH 2, 80 °C, and characterized their hydrolysis, assembly kinetics, and morphology. A lag phase was absent from the fibrillation kinetics of pea and soy 7S globulins, while 11S globulins and crude extracts displayed a similar lag time. Pea and soy protein fibrils differed in morphology, with most pea fibrils being straight and soy fibrils being worm-like. Pea and soy globulins were abundant in amyloid-forming peptides, with over 100 unique fibril-core peptides from pea 7S and around 50 unique fibril-core peptides identified from pea 11S, soy 7S, and soy 11S globulins. Amyloidogenic regions derive predominantly from the homologous core region of 7S globulins and the basic subunit of 11S globulins. Overall, pea and soy 7S and 11S globulins are rich in amyloidogenic regions. This study will help understand their fibrillation mechanism and engineer protein fibrils with specific structures and functionality.

Fibrillization kinetics and rheological properties of panda bean (Vigna umbellata (Thunb.) Ohwi et Ohashi) protein isolate at pH 2.0

Recently, research interests are growing regarding the formation and mechanisms of amyloid fibrils from plant proteins. This study investigated the fibrillization kinetics and rheological behaviors of panda bean protein isolate (PBPI) at pH 2.0 and 90 °C for various heating times (0-24 h). Results showed that PBPI formed two distinct classes of fibrils after heating for 10 h, including flexible fibril with a contour length of ∼751 nm, and rigid fibril with periodicity of ∼40 nm. The secondary structural changes during fibril formation were monitored by circular dichroism spectroscopy and indicated that β-sheet content increased first (0-12 h) and then decreased (>12 h), which coincided with similar changes in thioflavin T fluorescence. The gel electrophoresis revealed that the polypeptides of PBPI were progressively hydrolyzed upon heating, and the resulting short fragments were involved in fibril formation rather than PBPI monomer. PBPI-derived fibrils showed extremely high viscosity and storage modulus. A plausible molecular mechanism for PBPI fibrillation process was hypothesized, including protein unfolding, hydrolysis, assembly into matured fibrils, and dissociation of the fibrils. The findings provide useful information to manipulate the formation of legume proteins-based fibrils and will benefit future research to explore their potential applications.

Understanding the differences in heat-induced gel properties of twelve legume proteins: A comparative study

This study aimed to investigate the rheological and textural properties of heat-induced gels from twelve legume protein isolates at pH 3.0 and 7.0, including black kidney bean (BKPI), speckled kidney bean (SKPI), panda bean (PDPI), cowpea (CPPI), mung bean (MPI), adzuki bean (API), rice bean (RPI), black soybean (BPI), soybean (SPI), chickpea (CPI), broad bean (BRPI) and pea (PPI). SDS-PAGE revealed that 7S globulin was prominent protein in BKPI, SKPI, PDPI, CPPI, MPI, API and RPI, the main protein fraction of CPI was 11S globulin, and BPI, SPI, BRPI and PPI contained both 7S and 11S globulins as major components. Based on the gel's Power Law constant (K') and hardness, twelve legume proteins were divided into three categories with high, medium and low gel strength. BKPI, SKPI and PDPI with Phaseolin being the major protein fraction showed high gel strength regardless of pH. Electrostatic interactions, hydrophobic interactions and hydrogen bonds were the most important intermolecular forces in the formation of legume protein gel networks, of which gel strength at pH 3.0 and pH 7.0 was significantly affected by electrostatic interactions and hydrogen bonds, respectively. Moreover, gel strength was also remarkably negatively influenced by the non-network proteins. SEM observation indicated that the microstructure of gels at pH 7.0 was denser and more homogeneous than that at pH 3.0, leading to better water holding capacity. These findings would be of great importance for understanding the differences in legume protein gels, and also laid the scientific support for expanding applications of legume proteins in gel-based foods.

Nanofibrils of food-grade proteins: Formation mechanism, delivery systems, and application evaluation

Due to the high aspect ratio, appealing mechanical characteristics, and various adjustable functional groups on the surface proteins, food-grade protein nanofibrils have attracted great research interest in the field of food science. Fibrillation, known as a process of peptide self-assembly, is recognized as a common attribute for food-grade proteins. Converting food-grade proteins into nanofibrils is a promising strategy to broaden their functionality and applications, such as improvement of the properties of gelling and emulsifying, especially for constructing various delivery systems for bioactive compounds. Protein source and processing conditions have a great impact on the size, structure, and morphology of nanofibrils, resulting in extreme differences in functionality. With this feature, it is possible to engineer nanofibrils into four different delivery systems, including gels, microcapsules, emulsions, and complexes. Construction of nanofibril-based gels via multiple cross-linking methods can endow gels with special network structures to efficiently capture bioactive compounds and extra mechanical behavior. The adsorption behavior of nanofibrils at the interface is highly complex due to the influence of several intrinsic factors, which makes it challenging to form stabilized nanofibril-based emulsion systems. Based on electrostatic interactions, microcapsules and complexes prepared using nanofibrils and polysaccharides have combined functional properties, resulting in adjustable release behavior and higher encapsulation efficiency. The bioactive compounds delivery system based on nanofibrils is a potential solution to enhance their absorption in the gastrointestinal tract, improve their bioavailability, and deliver them to target organs. Although food-grade protein nanofibrils show unknown toxicity to humans, further research can contribute to broadening the application of nanofibrils in delivery systems.

Protein nanofibrils as versatile and sustainable adsorbents for an effective removal of heavy metals from wastewater: A review

Water is a valuable natural resource, which plays a crucial role in ecological survival as well as economic progress. However, the water quality has deteriorated in recent years as a result of urbanization, industrialization and human activities due to the uncontrolled release of industrial wastes, which can be extremely carcinogenic and non-degradable, in air, water and soil bodies. Such wastes showed the presence of organic and inorganic pollutants in high dosages. Heavy metals are the most obstinate contaminants, and they can be harmful because of having a variety of detrimental consequences to the ecosystem. The existing water treatment methods in many situations may not be sustainable or effective because of their high energy requirements and ecological impacts. In this review, state-of-the-art water treatment methods for the elimination of heavy metals with the help of protein nanofibrils are covered featuring a discussion on the strategies and possibilities of developing protein nanofibrils for the active elimination of heavy metals using kitchen waste as well as residues from the cattle, agriculture, and dairy industries. Further, the emphasis has been given to their environmental sustainability and economical aspects are also discussed.

A combination of alkaline pH-shifting/acidic pH and thermal treatments improves the solubility and emulsification properties of wheat glutenin

Glutenin has limited applicability in food industry due to poor water solubility and emulsifying properties. In this study, the physicochemical properties of glutenin were improved by combined treatments of alkaline pH-shifting or acidic pH with heating. The surface morphology, structure and physicochemical properties were measured during the modification process of glutenin. Results showed that the smaller square clusters and regular tubular fibrils were observed in modified glutenin and the α-helix proportion of the treated glutenin was finally increased to 59.90 ± 0.01%. Compared with untreated glutenin, the combined treatments of pH-shifting with heating as well as fibrillation process increased the solubility of glutenin by 21.3 and 3.5 times, respectively. Moreover, the treated glutenin showed excellent emulsifying stability (EAI: 50.84 ± 0.51 m²g^-1) and thermal stability (peak temperature increased from 109.58 to 149.05 °C). This study provides an informative basis for improving the physicochemical and functional properties of glutenin.

Plant protein-based fibers: Fabrication, characterization, and potential food applications

Proteins from plants have been considered as safer, healthier, and more sustainable resources than their animal counterparts. However, incomplete amino acid composition and relatively poor functionality limit their applications in foods. Structuring plant proteins to fibrous architectures enhances their physicochemical properties, which can favor various food applications. This review primarily focuses on fabrication of fibers from plant proteins via self-assembly, electrospinning, solution blow spinning, wet spinning, and high-temperature shear, as well as on several applications where such fibrous proteins assemble in quality foods. The changes of protein structure and protein-protein interactions during fiber production are discussed in detail, along with the effects of fabrication conditions and protein sources on the morphology and function of the fibers. Self-assembly requires proteolysis and subsequent peptide aggregation under specific conditions, which can be influenced by pH, salt and protein type. The spinning strategy is more scalable and produces uniformed fibers with larger length scales suitable for encapsulation, food packaging and sensor substrates. Significant progress has been made on high-temperature shear (including extrusion)-induced fibers responsible for desirable texture in meat analogues. Structuring plant proteins adds values for broadened food applications, but it remains challenging to keep processes cost-effective and environmentally friendly using food grade solvents.

Protein nanofibrils and their use as building blocks of sustainable materials

The development towards a sustainable society requires a radical change of many of the materials we currently use. Besides the replacement of plastics, derived from petrochemical sources, with renewable alternatives, we will also need functional materials for applications in areas ranging from green energy and environmental remediation to smart foods. Proteins could, with their intriguing ability of self-assembly into various forms, play important roles in all these fields. To achieve that, the code for how to assemble hierarchically ordered structures similar to the protein materials found in nature must be cracked. During the last decade it has been demonstrated that amyloid-like protein nanofibrils (PNFs) could be a steppingstone for this task. PNFs are formed by self-assembly in water from a range of proteins, including plant resources and industrial side streams. The nanofibrils display distinct functional features and can be further assembled into larger structures. PNFs thus provide a framework for creating ordered, functional structures from the atomic level up to the macroscale. This review address how industrial scale protein resources could be transformed into PNFs and further assembled into materials with specific mechanical and functional properties. We describe what is required from a protein to form PNFs and how the structural properties at different length scales determine the material properties. We also discuss potential chemical routes to modify the properties of the fibrils and to assemble them into macroscopic structures.

Evolution of physicochemical and antioxidant properties of whey protein isolate during fibrillization process

Whey protein isolate (WPI) fibrils have great potential for applications in future food manufacture due to their improved properties. However, the evolution of their properties during fibrillization is still not fully understood. Here, we investigate variational characteristics of WPI fibrils during formation process. WPI fibrils with a semiflexible and linear structure were formed and showed high aspect ratio after heat treatment. The conversion, fluorescence intensity and isoelectric point of WPI were increased with heating time. Moreover, the antioxidant activity of WPI was improved after fibrillization and was dependent on heating time. This could be attributed to the structure transformation of protein and the exposed amino acids with sulfur groups or aromatic side chains in the fibrillated system. Our findings move a step forward for a detailed understanding on the dynamical changes of WPI properties during fibrillization, which would provide a guidance for WPI fibril applications and future food technology development.

Formation, structural characteristics, foaming and emulsifying properties of rice glutelin fibrils

The rice glutelin fibrils (RGFs) were formed under heating at acidic condition, and the optimal condition was achieved at pH 2, 150 mM (ionic strength), 4% (protein concentration), 90 °C and 300 rpm (stirring speed) through the thioflavin T intensity. The atomic force microscopy images showed that the average contour length of RGFs increased from < 100 to 365 nm under the optimal fibrillation. The average particle size of rice glutelin (RG) decreased from 650 to 221 nm after initial heating time. Combining the degraded subunits, it suggested that RG was hydrolyzed to peptides, then these released peptides assembled into the ordered fibrils via intermolecular interactions, accompanying by the structural rearrangement. Additionally, the foaming and emulsifying properties were improved during fibrillation, which could be related to the interfacial properties and structure of RGFs. This work will deepen the understanding of the formation of RGFs and explore their potential application.

Food protein amyloid fibrils: Origin, structure, formation, characterization, applications and health implications

Amyloid fibrils have traditionally been considered only as pathological aggregates in human neurodegenerative diseases, but it is increasingly becoming clear that the propensity to form amyloid fibrils is a generic property for all proteins, including food proteins. Differently from the pathological amyloid fibrils, those derived from food proteins can be used as advanced materials in biomedicine, tissue engineering, environmental science, nanotechnology, material science as well as in food science, owing to a combination of highly desirable feature such as extreme aspect ratios, outstanding stiffness and a broad availability of functional groups on their surfaces. In food science, protein fibrillization is progressively recognized as an appealing strategy to broaden and improve food protein functionality. This review article discusses the various classes of reported food protein amyloid fibrils and their formation conditions. It furthermore considers amyloid fibrils in a broad context, from their structural characterization to their forming mechanisms and ensued physical properties, emphasizing their applications in food-related fields. Finally, the biological fate and the potential toxicity mechanisms of food amyloid fibrils are discussed, and an experimental protocol for their health safety validation is proposed in the concluding part of the review.

Structural basis for the formation of soy protein nanofibrils

Amyloid-like protein nanofibrils (PNFs) can assemble from a range of different proteins including disease-associated proteins, functional amyloid proteins and several proteins for which the PNFs are neither related to disease nor function. We here examined the core building blocks of PNFs formed by soy proteins. Fibril formation at pH 2 and 90 °C is coupled to peptide hydrolysis which allows isolation of the PNF-forming peptides and identification of them by mass spectrometry. We found five peptides that constitute the main building blocks in soy PNFs, three of them from the protein β-conglycinin and two from the protein glycinin. The abilities of these peptides to form PNFs were addressed by amyloid prediction software and by PNF formation of the corresponding synthetic peptides. Analysis of the structural context in the native soy proteins revealed two structural motifs for the PNF-forming peptides: (i) so-called β-arches and (ii) helical segments involved in quaternary structure contacts. However, the results suggest that neither the native structural motifs nor the protein of origin defines the morphology of the PNFs formed from soy protein isolate.

Identification of the peptide building blocks of soy protein nanofibrils provides new clues about the determinants of protein nanofibril morphology.

Comparative experiments of fibril formation from whey protein concentrate with homogeneous and secondary nuclei

Two types of special structures, homogeneous and secondary nuclei, form during fibril formation. The structural and functional properties of amyloid fibrils in whey protein concentrate (WPC) with different ratios of added homogeneous nuclei to secondary nuclei were investigated. Thioflavin T fluorescence analysis and kinetic equations indicated that two types of nuclei could accelerate WPC fibrillation compared with WPC self-assembling into amyloid fibrils, thereby reducing the lag time and increasing the number of fibrils. However, there were considerable differences in the nucleation-inducing capability of WPC fibrillation between homogeneous and secondary nuclei. The number of fibrils formed by adding homogeneous nuclei was higher than that obtained with secondary nuclei, the increase in the Th T fluorescence intensity induced by homogeneous nuclei was 1.83-fold much than secondary nuclei. Meanwhile, secondary nuclei yielded a 2.71-fold faster aggregation rate of WPC than homogeneous nuclei, particularly during the first hour of thermal treatment (protein mass ratio of nuclei to WPC 1:1). The gelation time of WPC after secondary nuclei addition was shorter, from 10 h (WPC (2.0/6.5)) to 4 h (WPC + HN) to 2 h (WPC + SN); however, the gel microstructure of WPC after the addition of homogeneous nuclei was denser, yielding a preferred water holding capacity.

On the role of peptide hydrolysis for fibrillation kinetics and amyloid fibril morphology

Self-assembly of proteins into amyloid-like nanofibrils is not only a key event in several diseases, but such fibrils are also associated with intriguing biological function and constitute promising components for new biobased materials. The bovine whey protein β-lactoglobulin has emerged as an important model protein for the development of such materials. We here report that peptide hydrolysis is the rate-determining step for fibrillation of β-lactoglobulin in whey protein isolate. We also explore the observation that β-lactoglobulin nanofibrils of distinct morphologies are obtained by simply changing the initial protein concentration. We find that the morphological switch is related to different nucleation mechanisms and that the two classes of nanofibrils are associated with variations of the peptide building blocks. Based on the results, we propose that the balance between protein concentration and the hydrolysis rate determines the structure of the formed nanofibrils.

Peptide hydrolysis determines the fibrillation rate and the morphology of amyloid-like nanofibrils formed by β-lactoglobulin at low pH.

Formation of amyloid fibrils from soy protein hydrolysate: Effects of selective proteolysis on β-conglycinin

The soy protein hydrolysate subjected to selective proteolysis on β-conglycinin (referred to as DβH, contrast group) and a control soy protein isolate sample without addition of protease (referred to as CSPI, blank group) were adopted as experimental samples. By employing the "subtraction" mode of logical thinking, we aimed to compare the differences between CSPI and DβH on fibrillation at pH2.0 with heating at 95°C. The results showed when heated for 60min, CSPI tended to form short worm-like fibrils while DβH long semiflexible fibrils. When heating time was prolonged to 360min, the fibrils formed from them both exhibited cluster. Whereas when heated for 720min, no fibrillar aggregates appeared from them. This study would help explore the effects of β-conglycinin on the fibril formation of soy protein isolate by a new way.

Formation of heat-induced cottonseed congossypin(7S) fibrils at pH 2.0

BACKGROUND

Heat-induced protein aggregation is important for the texture of various food products. Many types of food proteins have been found to assemble into fibrillar structures under certain conditions. We studied fibril formation of cottonseed 7S storage protein upon heating (for 0-720 min) at 90°C and pH 2.0, investigated the conversion rate, and determined the extent of thermal aggregation.

RESULTS

Thioflavin-T fluorescence and Congo-red analysis indicated the formation of amyloid-like fibrils upon heating. Centrifugal filtration indicated that the conversion was very low (<10%) until congossypin concentration up to 2 mg mL(-1), and the conversion increases with increasing heating time, but levels off after longer heating times. Dynamic light scattering and atomic force microscopy showed that the extent of thermal aggregation at pH 2.0, or contour length of the worm-like and fine-stranded aggregates, progressively increased with increasing heating time. Furthermore, reducing electrophoresis analyses indicated that progressive polypeptide hydrolysis occurred upon heating. Experiments indicate that congossypin can form heat-induced amyloid-like aggregates and the conversion of congossypin monomers into fibrils increased with heating time and protein concentration.

CONCLUSION

The results would be of vital importance for the utilisation of cottonseed proteins to produce thermally induced fibrillar gels with excellent properties.

Fibril formation from pea protein and subsequent gel formation

The objective of this study was to characterize fibrillar aggregates made using pea proteins, to assemble formed fibrils into protein-based gels, and to study the rheological behavior of these gels. Micrometer-long fibrillar aggregates were observed after pea protein solutions had been heated for 20 h at pH 2.0. Following heating of pea proteins, it was observed that all of the proteins were hydrolyzed into peptides and that 50% of these peptides were assembled into fibrils. Changes on a structural level in pea proteins were studied using circular dichroism, transmission electron microscopy, and particle size analysis. During the fibril assembly process, an increase in aggregate size was observed, which coincided with an increase in thioflavin T binding, indicating the presence of β-sheet aggregates. Fibrils made using pea proteins were more branched and curly. Gel formation of preformed fibrils was induced by slow acidification from pH 7.0 to a final pH of around pH 5.0. The ability of pea protein-based fibrillar gels to fracture during an amplitude sweep was comparable to those of soy protein and whey protein-based fibrillar gels, although gels prepared from fibrils made using pea protein and soy protein were weaker than those of whey protein. The findings show that fibrils can be prepared from pea protein, which can be incorporated into protein-based fibrillar gels.