Ultrasonic Characterization of Amyloid-Like Ovalbumin Aggregation

Preventing thermal aggregation of ovalbumin through dielectric-barrier discharge plasma treatment and enhancing its emulsification properties

The impact of Dielectric-Barrier Discharge (DBD) plasma treatment on the prevention of heat-induced aggregation of Ovalbumin (OVA) and improvement in emulsification properties was investigated. Results highlighted the effective inhibition of thermal aggregation of OVA following exposure to plasma. Structural analysis revealed that the plasma-induced oxidation of sulfhydryl and intermolecular disulfide bonds played a pivotal role in inhibiting the thermal aggregation, considered by Sodium Dodecyl Sulfate Polyacrylamide Gel Electrophoresis (SDS-PAGE), multiplies spectroscopy, and analysis of dynamic exchange of sulfhydryl-disulfide bonds. Meanwhile, the oxidation of exposed hydrophobic sites due to plasma treatment resulted in the transformation of the OVA molecule's surface from hydrophobic to hydrophilic, contributing significantly to the aggregation inhibition. Additionally, compared to an untreated sample of OVA, almost one-fold increase in emulsifying ability (EAI) and 1.5-fold in emulsifying stability (ESI) was observed after 4 min of plasma treatment. These findings demonstrated that plasma treatment not only enhanced the thermal stability of OVA, but also improved its emulsification properties.

Fabrication mechanism and functional properties of ovalbumin fibrils prepared by acidic heat treatment

BACKGROUND

Ovalbumin (OVA), accounting for 50% of proteins in egg white, is a kind of high-quality protein with excellent nutritional and processing functions. Acid heat treatment will induce the deformation and filtration of OVA, endowing it with improved functionality. However, the molecular kinetic process during the fibrillation of OVA and the application of the fabricated OVA fibrils (OVAFs) have not been thoroughly studied and revealed.

RESULTS

In this study, the fabrication mechanism and the application OVAFs as an interfacial stabilizer and polyphenol protector were investigated. Acidic (pH 3.0) heat treatment was used to induce the fibrillation of OVA, and thioflavin T fluorescence intensity, molecular weight distribution, and the tertiary and secondary structures of OVAF samples were recorded to determine the fibrillation efficiency and the molecular mechanism. The results showed that, in the initial stage of fibrillation, OVA first hydrolyzed to oligopeptides, accompanied by the exposure of hydrophobic domains. Then, oligopeptides were connected by disulfide bonds to form primary fibril monomers. Hydrophobic interaction and hydrogen bonding may participate in the further polymerization of the fibrils. The fabricated OVAFs were characterized by a β-sheet-rich structure and possessed improved emulsifying, foaming, and polyphenol protection ability.

CONCLUSION

The research work was meaningful for exploring the application of globular water-soluble OVA in an emerging nutritious food with novel texture and sensory properties. © 2023 Society of Chemical Industry.

Ultrasonically Assisted N-Cyanoacylation and Synthesis of Alkyl(4-(3-cyano-4,6-dimethyl-2-oxopyridin-1(2H)-yl)benzoyl)amino Acid Ester Derivatives

This work represents the use of N-3-(3,5-dimethyl-1H-pyrazol-1-yl)-3-oxopropanenitrile as a cyanoacetylating agent for the synthesis of cyanoacetamide benzoic acid and benzophenone derivatives by two different methods, namely, conventional heating and ultrasonication. The cyanoacetamide derivatives were subjected to cyclization to produce N-substituted 2-pyridone derivatives under conventional heating and by an ultrasonic method as well. The ultrasonic method afforded the products in less reaction time with high yields and purities compared to the conventional method, as observed from their spectral data. N-(4-Carboxy phenyl)-4,6-dimethyl-3-cyano-2-pyridone was coupled with different amino acid esters by the OxymaPure/DIC methodology under traditional and ultrasonic conditions. Again, ultrasonication assisted the coupling step and afforded the products with higher yields and purities compared to the traditional method. Fourier transform infrared spectroscopy, NMR (¹H and ¹³C), elemental analysis, and LC-MS were used to determine the structures of all compounds. Finally, a feature of this protocol is exploring the utilization of ultrasonication as an eco-friendly alternative conventional heating method for N-cyanoacylation and synthesis of N-substituted pyridinone derivatives and as a coupling method for the formation of an amide bond, which might be of interest for many researchers.

Characterization of the ergometric properties of commercial bioactive dairy peptides

The thermodynamic properties of bioactive peptides provide insights into their functional behavior and their biological efficacy. We conducted precise analyses of the density, the ultrasonic velocity and the relative attenuation of serial dilutions of three commercial dairy peptides prepared by enzymatic methods. From these we determined the partial specific volume and the partial specific adiabatic compressibility coefficient for the peptides. At concentrations greater than ~2.5 ​mg ​mL⁻¹, the apparent values for specific volume and adiabatic compressibility were constant, differing between the three peptides at ±3% for specific volume and ±70% for compressibility. Both specific volume and adiabatic compressibility were highly dependent on concentration, indicating the importance of precise low concentration measurements to obtain correct values for these thermodynamic parameters. From these parameters it was apparent that restructuring of water molecules around the peptides (and their associated counterions) led to compact solutes that were also incompressible. These thermodynamic analyses are critical for understanding how the properties and the beneficial effects of bioactive peptides are influenced by their chemical environment.

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Dissolved dairy peptide properties distinguishable from ergometric analyses.

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Specific volume and adiabatic compressibility evaluate bioactive peptide hydration.

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Commercial bioactive dairy peptides are compact and incompressible.

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Compactness and incompressibility of peptide affected by hydrogen-bonding amino acids.

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Solution concentration affects values of measured thermodynamic parameters.

Processing Induced Changes in Food Proteins: Amyloid Formation during Boiling of Hen Egg White

Amyloid fibrils (AFs) are highly ordered protein nanofibers composed of cross β-structure that occur in nature, but that also accumulate in age-related diseases. Amyloid propensity is a generic property of proteins revealed by conditions that destabilize the native state, suggesting that food processing conditions may promote AF formation. This had only been shown for foie gras, but not in common foodstuffs. We here extracted a dense network of fibrillar proteins from commonly consumed boiled hen egg white (EW) using chemical and/or enzymatic treatments. Conversion of EW proteins into AFs during boiling was demonstrated by thioflavin T fluorescence, Congo red staining, and X-ray fiber diffraction measurements. Our data show that cooking converts approximately 1-3% of the protein in EW into AFs, suggesting that they are a common component of the human diet.

Conditions Governing Food Protein Amyloid Fibril Formation-Part I: Egg and Cereal Proteins

Conditions including heating mode, time, temperature, pH, moisture and protein concentration, shear, and the presence of alcohols, chaotropic/reducing agents, enzymes, and/or salt influence amyloid fibril (AF) formation as they can affect the accessibility of amino acid sequences prone to aggregate. As some conditions applied on model protein resemble conditions in food processing unit operations, we here hypothesize that food processing can lead to formation of protein AFs with a compact cross β-sheet structure. This paper reviews conditions and food constituents that affect amyloid fibrillation of egg and cereal proteins. While egg and cereal proteins often coexist in food products, their impact on each other's fibrillation remains unknown. Hen egg ovalbumin and lysozyme form AFs when subjected to moderate heating at acidic pH separately. AFs can also be formed at higher pH, especially in the presence of alcohols or chaotropic/reducing agents. Tryptic wheat gluten digests can form fibrillar structures at neutral pH and maize and rice proteins do so in aqueous ethanol or at acidic pH, respectively.

Rational Design of Amyloid-Like Fibrillary Structures for Tailoring Food Protein Techno-Functionality and Their Potential Health Implications

To control and enhance protein functionality is a major challenge for food scientists. In this context, research on food protein fibril formation, especially amyloid fibril formation, holds much promise. We here first provide a concise overview of conditions, which affect amyloid formation in food proteins. Particular attention is directed towards amyloid core regions because these sequences promote ordered aggregation. Better understanding of this process will be key to tailor the fibril formation process. Especially seeding, that is, adding preformed protein fibrils to protein solutions to accelerate fibril formation holds promise to tailor aggregation and fibril techno-functionality. Some studies have already indicated that food protein fibrillation indeed improves their techno-functionality. However, much more research is necessary to establish whether protein fibrils are useful in complex food systems and whether and to what extent they resist food processing unit operations. In this review the effect of amyloid formation on gelation, interfacial properties, foaming, and emulsification is discussed. Despite their prevalent role as functional structures, amyloids also receive a lot of attention due to their association with protein deposition diseases, prompting us to thoroughly investigate the potential health impact of amyloid-like aggregates in food. A literature review on the effect of the different stages of the human digestive process on amyloid toxicity leads us to conclude that food-derived amyloid fibrils (even those with potential pathogenic properties) very likely have minimal impact on human health. Nevertheless, prior to wide-spread application of the technology, it is highly advisable to further verify the lack of toxicity of food-derived amyloid fibrils.