Oxidative modification of soy protein by peroxyl radicals

Carvacrol-loaded nanoemulsions stabilized by soy protein isolate / chitooligosaccharide conjugates inhibited the oxidation and conformational variations of myofibrillar proteins in refrigerated sea bass (Lateolabrax maculatus)

Soy isolate protein / chitooligosaccharide (SPI/COS) glycosylated conjugates was prepared and employed as an emulsifier to stabilize carvacrol-loaded nanoemulsions (CNE-SPI/COS). The effects of CNE-SPI/COS on the oxidation and aggregation of myofibrillar protein (MPs) from sea bass (Lateolabrax maculatus) were investigated. Samples were immersed in sterile water (CK), SPI/COS solution and CNE-SPI/COS solution, respectively, follow by a 15-day refrigerated storage. MPs were extracted from fish fillets at 3-day intervals, then assessed for the oxidation degree and conformational changes in MPs, as well as structural variations in myofibrils. Compared with the CK group, the results obtained from protein oxidation assessment clarified that the oxidation and aggregation of MPs was significantly reduced by the CNE-SPI/COS treatment, as evidenced by the higher total sulfhydryl content and Ca2+-ATPase activity and lower surface hydrophobicity. Conformational analysis of MPs showed that CNE-SPI/COS was effective in maintaining the ordered secondary structure of MPs and reducing the exposure of hydrophobic residues in the hydrophobic core of the tertiary structure. In addition, CNE-SPI/COS was found to be effective in protecting the microstructure of muscle fibers and myofibrils in fish fillets. These results suggest that CNE-SPI/COS can be a promising method to prevent protein oxidation and aggregation in fish.

Effects of thermal treatment on the formation and properties of whey protein isolate/whey protein hydrolysate-sodium hyaluronate complexes

In dairy products, the added sodium hyaluronate may form complexes with proteins, thereby affecting product properties. In the present study, the interaction between whey protein isolate (WPI)/ whey protein hydrolysate (WPH) and sodium hyaluronate (SH) was characterized under thermal treatment at different temperatures (25 ℃, 65 ℃, 90 ℃ and 121 ℃) after studying effects of protein/SH ratio and pH on complex formation. The addition of SH reduced the particle size of WPI/WPH and increased potential value in the system, with greater variation with increasing treatment temperature. The structural properties of complexes were studied. The binding with SH decreased the contents of free amino group and free thiol group, as well as the fluorescence intensity and surface hydrophobicity. FTIR results and browning intensity measurement demonstrated the formation of Maillard reaction products. Moreover, the attachment of SH improved the thermal stability of WPI/WPH and decreased their antigenicity.

Effect of Alkyl Peroxyl Radical Oxidation on the Oxidative Stability of Walnut Protein Emulsions and Their Adsorbed Proteins

Walnuts are high in protein content and rich in nutrients and are susceptible to oxidation during production and processing, leading to a decrease in the stability of walnut protein emulsions. In this paper, the effect of alkyl peroxyl radical oxidation on the stability of walnut protein emulsions is investigated. With the increase of 2,2-azobis (2-methylpropionamidine) dihydrochloride (AAPH) concentration, both its protein and fat were oxidized to different degrees, and the droplets of the emulsion were first dispersed and then aggregated as seen from the laser confocal, and the stability of walnut protein emulsion was best at the AAPH concentration of 0.2 mmol/L. In addition to this, the adsorption rate of adsorbed proteins showed a decreasing and then an increasing trend with the increase in the oxidized concentration. The results showed that moderate oxidation (AAPH concentration: 0-0.2 mmol/L) promoted an increase in protein flexibility and a decrease in the protein interfacial tension, leading to the decrease in emulsion droplet size and the increase of walnut protein emulsion stability, and excessive oxidation (AAPH concentration: 1-25 mmmol/L) weakened protein flexibility and electrostatic repulsion, making the walnut protein emulsion less stable. The results of this study provide theoretical references for the quality control of walnut protein emulsions.

Effects of Baking and Frying on the Protein Oxidation of Wheat Dough

Protein oxidation caused by food processing is harmful to human health. A large number of studies have focused on the effects of hot processing on protein oxidation of meat products. As an important protein source for human beings, the effects of hot processing on protein oxidation in flour products are also worthy of further study. This study investigated the influences on the protein oxidation of wheat dough under baking (0-30 min, 200 °C or 20 min, 80-230 °C) and frying (0-18 min, 180 °C or 10 min, 140-200 °C). With the increase in baking and frying time and temperature, we found that the color of the dough deepened, the secondary structure of the protein changed from α-helix to β-sheet and β-turn, the content of carbonyl and advanced glycation end products (AGEs) increased, and the content of free sulfhydryl (SH) and free amino groups decreased. Furthermore, baking and frying resulted in a decrease in some special amino acid components in the dough, and an increase in the content of amino acid oxidation products, dityrosine, kynurenine, and N'-formylkynurenine. Moreover, the nutritional value evaluation results showed that excessive baking and frying reduced the free radical scavenging rate and digestibility of the dough. These results suggest that frying and baking can cause protein oxidation in the dough, resulting in the accumulation of protein oxidation products and decreased nutritional value. Therefore, it is necessary to reduce excessive processing or take reasonable intervention measures to reduce the effects of thermal processing on protein oxidation of flour products.

Structure and in vitro digestion characteristics of skim goat milk protein during processing: effects of fat separation

BACKGROUND

Although nonfat milk has been used worldwide in the industrial dairy process, little is known about the effects of fat separation during the manufacturing process on skim milk's structural and digestive properties. This study investigated the effects of the manufacturing process on the structure and in vitro digestion properties of skim goat milk, particularly emphasizing fat separation.

RESULTS

Changes in the surface charge and hydrophobicity of milk proteins caused by fat separation resulted in oxidation and aggregation in the subsequent homogenization, heat and spray-drying processing, which affected its digestibility. Compared with separation by dish separator (DS), skim milk after tubular centrifugal separation (CS) showed a higher initial and final digestibility. The CS samples also had a lower surface hydrophobicity level and higher free sulfhydryl content, ζ-potential, and average particle size (P < 0.05). Goat milk protein after CS was more readily oxidized and aggregated during the subsequent homogenization and heat treatment, as evidenced by the higher carbonyl content and particle size. Centrifugal separation also converted more β-sheets to α-helices, thus promoting the aggregation of oxidized skim milk protein.

CONCLUSION

The skim milk after CS and DS demonstrated different structural and digestive properties. Skim goat milk products after CS were more susceptible to oxidant-induced protein structural changes, resulting in higher protein digestibility. These findings provide insights into the mechanism involved in the control of gastric digestion of skim milk during manufacturing process. © 2023 Society of Chemical Industry.

Enhanced properties of non-starch polysaccharide and protein hydrocolloids through plasma treatment: A review

Hydrocolloids are important ingredients in food formulations and their modification can lead to novel ingredients with unique functionalities beyond their nutritional value. Cold plasma is a promising technology for the modification of food biopolymers due to its non-toxic and eco-friendly nature. This review discusses the recent published studies on the effects of cold plasma treatment on non-starch hydrocolloids and their derivatives. It covers the common phenomena that occur during plasma treatment, including ionization, etching effect, surface modification, and ashing effect, and how they contribute to various changes in food biopolymers. The effects of plasma treatment on important properties such as color, crystallinity, chemical structure, rheological behavior, and thermal properties of non-starch hydrocolloids and their derivatives are also discussed. In addition, this review highlights the potential of cold plasma treatment to enhance the functionality of food biopolymers and improve the quality of food products. The mechanisms underlying the effects of plasma treatment on food biopolymers, which can be useful for future research in this area, are also discussed. Overall, this review paper presents a comprehensive overview of the current knowledge in the field of cold plasma treatment of non-starch hydrocolloids and their derivatives and highlights the areas that require further investigation.

Effects of 2,2'-Azobis(2-methylpropionamidine) Dihydrochloride Stress on the Gel Properties of Duck Myofibrillar Protein Isolate

The aim of this study was to investigate the biochemical properties and gel-forming capacity of duck myofibrillar proteins under the effects of 2,2'-azobis(2-methylpropionamidine) dihydrochloride (AAPH)-mediated oxidation. Duck myofibrillar proteins were extracted and treated with different concentrations of AAPH solutions (0, 1, 3, 5, 10 mmol/L) and then analysed for carbonyl content, dynamic rheology, protein profiles and gel-forming properties (colour, water holding capacity, gel strength and microstructure). The results showed that with increasing AAPH concentration, the carbonyl content of the proteins exhibited an increasing trend (p < 0.05); SDS-PAGE pattern changes indicated that moderate oxidation (3 mmol/L AAPH) induced myosin aggregation via covalent bonds including disulfide, enhanced protein-protein interactions, and thus affected the gel strength of the DMPs' heat-induced gels. However, high oxidation (5 and 10 mmol/L AAPH) led to the partial degradation of the myosin heavy chain (MHC) isoforms, as evidenced by lower storage modulus and irregular microstructures, which significantly reduced gelation ability. These results suggest that the internal relationship between alkylperoxyl radical-induced oxidation should be taken into account in the processing of duck meat, as mild protein oxidation is conducive to improving gel quality.

The Impact of AAPH-Induced Oxidation on the Functional and Structural Properties, and Proteomics of Arachin

The aim of this study was to investigate the effect of 2,2'-azobis (2-amidinopropane) dihydrochloride (AAPH)-induced oxidation on the functional, structural properties and proteomic information of arachin. The results showed that moderate oxidation improved the water/oil holding capacity of proteins and increased the emulsifying stability, while excessive oxidation increased the carbonyl content, reduced the thiol content, altered the structure and thermal stability, and reduced most of the physicochemical properties. Through LC-QE-MS analysis, it was observed that oxidation leads to various modifications in arachin, including carbamylation, oxidation, and reduction, among others. In addition, 15 differentially expressed proteins were identified. Through gene ontology (GO) analysis, these proteins primarily affected the cellular and metabolic processes in the biological process category. Further Kyoto encyclopedia of genes and genomes (KEGG) analysis revealed that the "proteasome; protein processing in the endoplasmic reticulum (PPER)" pathway was the most significantly enriched signaling pathway during the oxidation process of arachin. In conclusion, this study demonstrated that AAPH-induced oxidation can alter the conformation and proteome of arachin, thereby affecting its corresponding functional properties. The findings of this study can potentially serve as a theoretical basis and foundational reference for the management of peanut processing and storage.

Efficient binding paradigm of protein and polysaccharide: Preparation of isolated soy protein-chitosan quaternary ammonium salt complex system and exploration of its emulsification potential

Soy protein isolate (SPI) has good emulsifying ability, but is greatly affected by the environment. The addition of polysaccharides either increases or decreases the stability of SPI. We report and prepared for the first time SPI/HACC complexes with different polysaccharide contents (SPI/HACC ratios are 1:1, 2:1 and 5:1). The binding properties, microstructure and emulsifying properties of the SPI/HACC complexes were determined and analyzed. The results showed that the interaction them is mainly through hydrogen bonding, electrostatic interaction, hydrophobic interaction and steric hindrance effect. The combination of SPI and HACC overcomes their respective limitations and the microstructure is more flat and smooth. It was also found that the emulsifying ability and concentration of SPI showed a certain correlation and the addition of HACC significantly improved the emulsifying ability and storage stability of SPI. This study shows that the prepared SPI/HACC complex has great potential for application in the food industry.

Study on the Structure, Function, and Interface Characteristics of Soybean Protein Isolate by Industrial Phosphorylation

The impacts of industrial phosphorylation on the structural changes, microstructure, functional, and rheological features of soybean protein isolate (SPI) were spotlighted. The findings implied that the spatial structure and functional features of the SPI changed significantly after treatment with the two phosphates. Sodium hexametaphosphate (SHMP) promoted aggregation of SPI with a larger particle size; sodium tripolyphosphate (STP) modified SPI with smaller particle size. SDS-polyacrylamide gel electrophoresis (SDS-PAGE) results showed insignificant alterations in the structure of SPI subunits. Fourier transform infrared (FTIR) and endogenous fluorescence noted a decline in α-helix quantity, an amplification in β-fold quantity, and an increase in protein stretching and disorder, indicating that phosphorylation treatment fluctuated the spatial structure of the SPI. Functional characterization studies showed that the solubility and emulsion properties of the SPI increased to varying degrees after phosphorylation, with a maximum solubility of 94.64% for SHMP-SPI and 97.09% for STP-SPI. Emulsifying activity index (EAI) and emulsifying steadiness index (ESI) results for STP-SPI were better than those for SHMP-SPI. Rheological results showed that the modulus of G' and G″ increased and the emulsion exhibited significant elastic behavior. This affords a theoretical core for expanding the industrial production applications of soybean isolates in the food and various industries.

Enhancing the Techno-Functionality of Pea Flour by Air Injection-Assisted Extrusion at Different Temperatures and Flour Particle Sizes

Industrial applications of pulses in various food products depend on pulse flour techno-functionality. To manipulate the techno-functional properties of yellow pea flour, the effects of flour particle size (small vs. large), extrusion temperature profile (120, 140 and 160 °C at the die) and air injection pressure (0, 150 and 300 kPa) during extrusion cooking were investigated. Extrusion cooking caused the denaturation of proteins and gelatinization of starch in the flour, which induced changes in the techno-functionality of the extruded flour (i.e., increased water solubility, water binding capacity and cold viscosity and decreased emulsion capacity, emulsion stability, and trough and final viscosities). In general, the large particle size flour required less energy input to be extruded and had higher emulsion stability and trough and final viscosities compared to the small particle size flour. Overall, among all of the treatments studied, extrudates produced with air injection at 140 and 160 °C had higher emulsion capacity and emulsion stability, making them relatively better suited food ingredients for emulsified foods (e.g., sausages). The results indicated air injection's potential as a novel extrusion technique combined with modification of flour particle size distribution and extrusion processing conditions to effectively manipulate product techno-functionality and broaden the applications of pulse flours in the food industry.

Effects of Packaging Materials on Structural and Simulated Digestive Characteristics of Walnut Protein during Accelerated Storage

Walnuts are rich in fat and proteins that become oxidized during the processing and storage conditions of their kernels. In this study, the effect of three packaging materials (e.g., polyethylene sealed packaging, polyamide/polyethylene vacuum packaging, and polyethylene terephthalate/aluminum foil/polyethylene vacuum packaging) were investigated on the oxidation, structural and digestive properties of walnut kernel proteins. Results showed that the amino acid content gradually decreased and carbonyl derivatives and dityrosine were formed during storage. The protein molecule structure became disordered as the α-helix decreased and the random coil increased. The endogenous fluorescence intensity decreased and the maximum fluorescence value was blue-shifted. After 15 days of storage, surface hydrophobicity decreased, while SDS-PAGE and HPLC indicated the formation of large protein aggregates, leading to a reduction in solubility. By simulating gastrointestinal digestion, we found that oxidation adversely affected the digestive properties of walnut protein isolate and protein digestibility was best for polyethylene terephthalate/aluminum foil/polyethylene vacuum packaging. The degree of protein oxidation in walnuts increased during storage, which showed that except for fat oxidation, the effect of protein oxidation on quality should be considered. The results of the study provided new ideas and methods for walnut quality control.

Potential implications of oxidative modification on dietary protein nutritional value: A review

During food processing and storage, proteins are sensitive to oxidative modification, changing the structural characteristics and functional properties. Recently, the impact of dietary protein oxidation on body health has drawn increasing attention. However, few reviews summarized and highlighted the impact of oxidative modification on the nutritional value of dietary proteins and related mechanisms. Therefore, this review seeks to give an updated discussion of the effects of oxidative modification on the structural characteristics and nutritional value of dietary proteins, and elucidate the interaction with gut microbiota, intestinal tissues, and organs. Additionally, the specific mechanisms related to pathological conditions are also characterized. Dietary protein oxidation during food processing and storage change protein structure, which further influences the in vitro digestion properties of proteins. In vivo research demonstrates that oxidized dietary proteins threaten body health via complicated pathways and affect the intestinal microenvironment via gut microbiota, metabolites, and intestinal morphology. This review highlights the influence of oxidative modification on the nutritional value of dietary proteins based on organs and the intestinal tract, and illustrates the necessity of appropriate experimental design for comprehensively exploring the health consequences of oxidized dietary proteins.

Effect of Oxidative Modification by Peroxyl Radical on the Characterization and Identification of Oxidative Aggregates and In Vitro Digestion Products of Walnut (Juglans regia L.) Protein Isolates

Walnut protein is a key plant protein resource due to its high nutritional value, but walnuts are prone to oxidation during storage and processing. This article explored the oxidative modification and digestion mechanism of walnut protein isolates by peroxyl radical and obtained new findings. SDS-PAGE and spectral analysis were used to identify structural changes in the protein after oxidative modification, and LC-MS/MS was used to identify the digestion products. The findings demonstrated that as the AAPH concentration increased, protein carbonyl content increased from 2.36 to 5.12 nmol/mg, while free sulfhydryl content, free amino content, and surface hydrophobicity decreased from 4.30 nmol/mg, 1.47 μmol/mg, and 167.92 to 1.72 nmol/mg, 1.13 μmol/mg, and 40.93 nmol/mg, respectively. Furthermore, the result of Tricine-SDS-PAGE in vitro digestion revealed that protein oxidation could cause gastric digestion resistance and a tendency for intestinal digestion promotion. Carbonyl content increased dramatically during the early stages of gastric digestion and again after 90 min of intestine digestion, and LC-MS/MS identified the last digestive products of the stomach and intestine as essential seed storage proteins. Oxidation causes walnut proteins to form aggregates, which are then re-oxidized during digestion, and proper oxidative modification may benefit intestinal digestion.

The temporal evolution mechanism of structure and function of oxidized soy protein aggregates

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The oxidation of soybean protein has the regular temporal evolution mechanism.

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The oxidation with proper time can enhance functionality properties of soy protein.

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Excessive oxidation leads to the decline of functionality properties of soy protein.

The emulsifying activity of soy protein would decrease after long-term storage, which caused huge economic losses to food processing plants. This study explored the temporal evolution mechanism of oxidation on the structure and function of soy protein aggregates, which would improve the application of soy protein in food industry. Decreased α-helix and increased random coil were observed at the initial oxidation stage (0–4 h), which induced increases in hydrophobicity and disulfide bond content. In addition, emulsibility increased significantly. However, when the oxidation time extended to 6–12 h, the soluble aggregates transformed into insoluble aggregates with large particle size, low solubility, and molecular flexibility. Surface hydrophobicity and emulsifying activity were reduced, resulting in bridging flocculation of emulsion droplets. Mutual transformation between components is affected by factors that include spatial conformation and intermolecular forces, which eventually lead to functional changes in the protein molecules.

Effects of Oxidation Modification by Malondialdehyde on the Structure and Functional Properties of Walnut Protein

(1) Background: The effects of protein oxidization induced by malondialdehyde (MDA), which was selected as a representative of lipid peroxidation products, on the structure and functional properties of walnut protein were investigated. (2) Methods: Walnut protein isolate was produced by alkali-soluble acid precipitation. The modification of walnut protein isolate was conducted by MDA solutions (0, 0.01, 0.1, 1, and 10 Mm), which were incubated in the dark for 24 h. (3) Results: Increased carbonyl content and the degradation of sulfhydryl groups indicated MDA-induced protein oxidization. The circular dichroism spectra revealed disruption of the ordered protein secondary structure. The change in the tertiary conformation of the MDA-treated protein was observed through intrinsic fluorescence. Small polypeptide chain scission was observed at low MDA concentrations (≤0.1 mM) and protein aggregation was observed at high MDA concentrations (>0.1 mM) using high-performance size exclusion chromatography. Oxidized protein solubility was reduced. Furthermore, the emulsification stability index, foam capacity, and foam stability of walnut proteins were increased after treatment with 0.1 mM of MDA. An excessive concentration of MDA (>0.1 mM) decreased emulsification and foaming properties. (4) Conclusions: These results show that MDA oxidation modified the structure of walnut protein and further affected its function, which should be taken into account in processing walnut protein products.

Functional and Allergenic Properties Assessment of Conalbumin (Ovotransferrin) after Oxidation

Conalbumin (CA) is an iron-binding egg protein that has various bioactivities and causes major allergenicity in humans. This study investigated how oxidation affects the multiple functional properties of CA. The lipid peroxidation method was used to prepare treated CA [2,2′-azobis (2-amidinopropane) dihydrochloride (AAPH)-CA and acrolein-CA] complexes. CA induced structural changes through oxidation. These changes enhanced the digestibility, rate of endocytosis in dendritic cells, and emulsifying and foaming properties of CA. ELISA and immunoblot analysis showed that the complexes reduced the IgE-binding ability of CA through lipid oxidation. KU812 cell assays showed that modification by AAPH and acrolein caused the release of IL-4 and histamine to decline. In conclusion, oxidation treatment modified the functional and structural properties of CA, reducing allergenicity during processing and preservation.

Resveratrol Stabilization and Loss by Sodium Caseinate, Whey and Soy Protein Isolates: Loading, Antioxidant Activity, Oxidability

The interaction of protein carrier and polyphenol is variable due to their environmental sensitivity. In this study, the interaction between resveratrol and whey protein isolate (WPI), sodium caseinate (SC) and soy protein isolate (SPI) during storage were systematically investigated from the aspects of polyphenol loading, antioxidant activity and oxidability. It was revealed that resveratrol loaded more in the SPI core and existed both in the core of SC micelles and on the particle surface, while WPI and resveratrol mainly formed in complexes. The loading capacity of the three proteins ranked in order SC > SPI > WPI. ABTS assay showed that the antioxidant activity of the protein carriers in the initial state was SC > SPI > WPI. The results of sulfhydryl, carbonyl and amino acid analysis showed that protein oxidability was SPI > SC > WPI. WPI, with the least oxidation, improved the storage stability of resveratrol, and the impact of SC on resveratrol stability changed from a protective to a pro-degradation effect. Co-oxidation occurred between SPI and resveratrol during storage, which refers to covalent interactions. The data gathered here suggested that the transition between the antioxidant and pro-oxidative properties of the carrier is the primary factor to investigate its protective effect on the delivered polyphenol.

Lipid oxidation induced egg white protein foaming properties enhancement: The mechanism study revealed by high resolution mass spectrometry

Lipid oxidation often occurs during egg white protein (EWP) storage and processing periods. Here, 2,2'-azobis (2-amidinopropane) dihydrochloride (AAPH) was performed to simulate lipid oxidation to probe the oxidation effects on foaming and structural properties of EWP. Results indicated that EWP structure became unfolding and flexible after oxidation, resulting in more hydrophobic groups and negative charge exposed and soluble aggregates formed, which revealed by the results of DLS and AFM. Additionally, high resolution mass spectrometry results evidenced that ovotransferrin and lysozyme trended to be new oxidation targets with the AAPH concentration increasing, and the oxidation sites inside lysozyme proved that EWP unfolding and exposure of internal hydrophobic amino acids, which were related to the enhancement of EWP foaming properties. Overall, our study provided a further analysis of the lipid induced oxidation of EWP, which may contribute to provide a more accurate strategy for enhancing protein foaming properties in food industry.

Faba bean protein: A promising plant-based emulsifier for improving physical and oxidative stabilities of oil-in-water emulsions

Faba bean is a protein-rich, sustainable, but understudied legume. Faba bean protein isolates (FBPIs) can serve as promising emulsifiers. This review aims to summarize the research on FBPIs as emulsifiers and various modification methods to improve the emulsifying functionalities. The emulsifying activities of FBPIs depend on several physiochemical characteristics (e.g. solubility, surface hydrophobicity, surface charge, interfacial activity). Physical modifications, especially via linking FBPIs electrostatically to polysaccharides can effectively increase the interfacial layer thickness/compactness and maintain the interfacial protein adsorption. Chemical modifications of FBPIs (e.g. acetylation and Maillard reaction) could improve the interfacial activity and affect the droplet-size distribution. Enzymatic modifications, usually either via hydrolysis or cross-linking, help to optimize the molecular size, solubility, and surface hydrophobicity of FBPIs. It is critical to consider the lipid/protein oxidative stability and physical stability when optimizing the emulsifying functionality of FBPIs. With suitable modifications, FBPI can serve as a promising emulsifier in food production.

Effect of ultrasonic on the structure and quality characteristics of quinoa protein oxidation aggregates

Protein oxidation leads to covalent modification of structure and deterioration of functional properties of quinoa protein. The objective of this study was to investigate the effects of ultrasonic treatment on the functional and physicochemical properties of quinoa protein oxidation aggregates. In this concern, 2,2'-azobis (2-amidinopropane) dihydrochloride (AAPH) was selected as oxidative modification of quinoa protein. The microstructure of quinoa protein displayed by scanning electron microscope (SEM) indicated that oxidation induced extensive aggregation, leading to carbonylation and degradation of sulfhydryl groups. Aggregation induced by oxidation had a negative effect on the solubility, turbidity, emulsifying stability. However, according to the analysis of physicochemical properties, ultrasonic significantly improved the water solubility of quinoa protein. The quinoa protein treated by ultrasonic for 30 min exhibited the best dispersion stability in water, which corresponded to the highest ζ-potential, smallest particle size and most uniform distribution. Based on the FT-IR, SDS-PAGE and surface hydrophobicity analysis, the increase of α-helix, β-turn and surface hydrophobicity caused by cavitation effect appeared to be the main mechanism of quinoa protein solubilization. In addition, the hydrophobic region of the protein was re-buried by excessive ultrasonic treatment, and the protein molecules were reaggregated by disulfide bonds. Microstructural observations further confirmed that ultrasonic treatment effectively inhibited protein aggregation and improved the functional properties of quinoa protein.

Quality Attributes of Ultra-High Temperature-Treated Model Beverages Prepared with Faba Bean Protein Concentrates

The objective of this research was to develop a model faba bean drink with a high concentration of protein (>4% w/w). The protein molecular weights and frequency for both faba and soy were assessed using SDS-PAGE. Results showed similarities in the protein molecular weight of both faba and soy (mainly 11S globulin ~Glycinin and 7S globulin ~β-conglycinin). Thus, faba can be considered as a potential soy replica in plant-based milk beverages. Oil-in-water emulsions (5-8% w/w available protein) were prepared using faba bean protein concentrate (FPC), 1% sunflower oil, and 0.2% sunflower lecithin. These emulsions were used as model beverages and were further investigated for UHT processibility, stability, and physicochemical properties. The physicochemical properties of emulsions at various processing stages viz., coarse emulsification, homogenisation, and UHT, were measured. An increase in the protein concentration and thermal treatment resulted in an increased oil droplet size, coalescence and flocculation, and protein aggregation. Lower protein concentrations viz., 5-6%, showed greater negative ζ-potential, and thereby, high dispersibility through enhanced electrostatic repulsions than those of higher concentrations (7-8%). Furthermore, an increase in protein concentration and UHT treatment resulted in an increased creaming index. In total, 21 different volatile compounds were detected and quantified, representing different chemical classes, namely alcohols, aldehydes, ketones, esters, furan, and acids. These volatiles have major consequences for the overall flavour chemistry of the model beverage product. Overall, this study showed the potential for application of faba bean as a protein source in UHT-treated legume-based beverages and identified areas for further development.

Reducing the Allergenicity of α-Lactalbumin after Lipid Peroxidation

This study analyzed the effect of lipid peroxidation using 2,2'-azobis(2-amidinopropane)dihydrochloride (AAPH) and acrolein on the in vitro and in vivo allergenicity of α-lactalbumin (α-La). The structure of oxidized α-La was evaluated by sodium dodecyl sulfate polyacrylamide gel electrophoresis, fluorescence spectroscopy, and circular dichroism, whereas the changes in the allergenic properties were evaluated. Lipid peroxidation induced changes to the structural properties that might destroy and/or mask α-La epitopes. In comparison to native α-La, oxidation complexes caused a decrease in the immunoglobulin E (IgE) binding capacity, as observed via immunoblotting. Moreover, the capacity to release mediators and cytokines from KU812 cells was also greatly reduced. In vivo, oxidation with AAPH and acrolein caused a significant reduction in IgE, IgG, IgG1, mast cell protease 1, and plasma histamine, along with the reduction of mast surface c-Kit⁺ and FcεRI⁺ expression. Therefore, these results indicate that oxidation via AAPH and acrolein can potentially reduce the allergenicity of α-La, which can help with the better understanding of the changes in allergenicity of milk allergen by lipid peroxidation.

Effects of oxidative modification of peroxyl radicals on the structure and foamability of chickpea protein isolates

A chickpea protein isolate (CPI) was oxidized using peroxyl radicals derived from 2,2'-azobis (2-amidopropane) dihydrochloride (AAPH), and the structural and foaming properties of the oxidized CPI were evaluated. The oxidation degree of protein was determined by measuring carbonyl content, dimer tyrosine content, free thiol content, and total thiol content. The structural changes of oxidized protein were evaluated by surface hydrophobicity, endogenous fluorescence intensity, Fourier transform infrared spectroscopy, SDS-PAGE, and amino acid content changes. Compared with the control group (0 mmol/L AAPH), moderate oxidation (0.04 mmol/L AAPH) led to the formation of a soluble protein with flexibility, which could improve the foaming properties of the protein (foaming capacity and stability increased by 25.50% and 6.38%, respectively). Over-oxidized (25 mmol/L AAPH) protein exhibited improved foaming capability, but its foam stability was reduced owing to the formation of insoluble aggregates. The results indicate that oxidation can change protein conformation, and the protein structure can affect the foamability of the CPI. PRACTICAL APPLICATION: CPI is a protein supplement food. Protein oxidation can occur during processing and storage, thereby affecting protein function. In this study, we evaluated how peroxy free radicals affect the structure, solubility and foaming properties of CPI, and clarified the mechanism between them. It has been found that peroxy free radicals can accelerate the oxidation of proteins and have a significant effect on foaming. Therefore, the degree of oxidation should be controlled to improve the quality of CPI.

Effect of MTGase on silver carp myofibrillar protein gelation behavior after peroxidation induced by peroxyl radicals

The objective of this study was to explore the oxidative modification induced by AAPH (2,2'-azobis (2-amidinopropane) dihydrochloride) on the microbial transglutaminase (MTGase) cross-linking reaction and gelling properties of silver carp myofibril protein (SCMP). Compared to AAPH treatment, MTGase addition resulted further changes of protein properties as evidenced by the decreasing free amino and thiol group content, the decreased secondary and tertiary structure, and the increasing storage modulus (G') and gel strength (P < 0.05). The proper oxidation induced by AAPH (5 mM) promoted the glutamine-lysine and disulfide cross-linking due to MTGase (10 U/g). Therefore, the quality of the SCMP gel was improved with a good water-holding capacity (WHC), gel strength and G'. This results could lay a theoretical foundation for the development of silver carp surimi products with good quality. Chemical compounds: (2,2'-azobis(2-amidinopropane)dihydrochloride (PubChem CID:76344); O-Phthalaldehyde (PubChem CID:4807); 5,5'-Dithiobis(2-Nitrobenzoic Acid) (PubChem CID:6254); 8-Anilino-1-naphthalenesulfonic acid (PubChem CID:1369); Acrylamide (PubChem CID: 6579); β-Mercaptoethanol (PubChem CID: 1567); Sodium dodecyl sulfate (PubChem CID:3423265).

Animal and Plant Protein Oxidation: Chemical and Functional Property Significance

Protein oxidation, a phenomenon that was not well recognized previously but now better understood, is a complex chemical process occurring ubiquitously in food systems and can be induced by processing treatments as well. While early research concentrated on muscle protein oxidation, later investigations included plant, milk, and egg proteins. The process of protein oxidation involves both radicals and nonradicals, and amino acid side chain groups are usually the site of initial oxidant attack which generates protein carbonyls, disulfide, dityrosine, and protein radicals. The ensuing alteration of protein conformational structures and formation of protein polymers and aggregates can result in significant changes in solubility and functionality, such as gelation, emulsification, foaming, and water-holding. Oxidant dose-dependent effects have been widely reported, i.e., mild-to-moderate oxidation may enhance the functionality while strong oxidation leads to insolubilization and functionality losses. Therefore, controlling the extent of protein oxidation in both animal and plant protein foods through oxidative and antioxidative strategies has been of wide interest in model system as well in in situ studies. This review presents a historical perspective of food protein oxidation research and provides an inclusive discussion of the impact of chemical and enzymatic oxidation on functional properties of meat, legume, cereal, dairy, and egg proteins based on the literature reports published in recent decades.

Effects of Cavitation Jet Treatment on the Structure and Emulsification Properties of Oxidized Soy Protein Isolate

This study examined the ability of cavitation jet processing to regulate the oxidation concentrations with 2,2'-azobis (2-amidinopropane) dihydrochloride (AAPH) (0.2, 1, and 5 mmol/L) and the structure and emulsification of soy protein isolate (SPI). The tested properties included particle size distribution, hydrophobic properties (sulfhydryl group (SH) and disulfide bond (S-S) contents, surface hydrophobicity (H0)), emulsifying properties (particle size and ζ-potential of emulsions, emulsification activity index (EAI), and emulsification stability index (ESI)), as well as conformational characteristics. The high shear force of cavitation jet treatment reduced the particle size of oxidized SPI and distributed uniformly. Cavitation jet (90 MPa)-treated SPI (AAPH with 1 mmol/L) demonstrated a high H0 (4688.70 ± 84.60), high EAI (71.78 ± 1.52 m2/g), and high ESI (86.73 ± 0.97%). The ordered secondary structure (α-helix and β-turn content) of SPI was enhanced by the cavitation jet. Meanwhile, the distribution of SPI-oxidized aggregates was observed under an atomic force microscope. Therefore, cavitation jet processing combined with oxidation treatment is an effective method to improve the characteristics of SPI and has potential industrial application prospects.

Atmospheric cold plasma treatment of soybean protein isolate: insights into the structural, physicochemical, and allergenic characteristics

Currently, there has been a surge of interest in revealing the interactions between plasma and food matrices. In this study, we investigated the impacts of atmospheric cold plasma (ACP) treatment on the structural, physicochemical and allergenic characteristics of soybean protein isolate (SPI). SPI dispersions were subjected to ACP treatments at different frequencies (80 to 100 Hz) and durations (1 to 10 min) to investigate the effects of exposing conditions. Results showed that ACP induced reactive oxygen species-mediated oxidation of soy proteins, resulting in modifications in the secondary and ternary structures of SPI. As a consequence, functional properties of SPI, such as emulsifying (56 to 168%, compared with control) and foaming properties (60 to 194%) were influenced by varying degrees. In addition, under certain circumstance (120 Hz, 5 min), the IgE-binding level of SPI was decreased by up to 75%, when compared to the control. Moderate treatment yielded products with improved functionality and reduced allergenicity, while extensive exposure induced a loss of vendibility due to protein aggregation. PRACTICAL APPLICATION: In this study, we demonstrated for the first time, that plasma species reacted with soybean proteins, resulting in spatial structural changes which are closely related with protein functionality and allergenicity. ACP interacts with macromolecules in aqueous systems and thus can be an alternative and promising nonthermal approach in modifying soybean proteins, whereas the exact role of different processing parameters needs to be well-elaborated.

Azocompounds as generators of defined radical species: Contributions and challenges for free radical research

Peroxyl radicals participate in multiple processes involved in critical changes to cells, tissues, pharmacueticals and foods. Some of these reactions explain their association with degenerative pathologies, including cardiovascular and neurological diseases, as well as cancer development. Azocompounds, and particularly AAPH (2,2'-Azobis(2-methylpropionamidine) dihydrochloride), a cationic water-soluble derivative, have been employed extensively as sources of model peroxyl radicals. A considerable number of studies have reported mechanistic data on the oxidation of biologically-relevant targets, the scavenging activity of foods and natural products, and the reactions with, and responses of, cultured cells. However, despite the (supposed) experimental simplicity of using azocompounds, the chemistry of peroxyl radical production and subsequent reactions is complicated, and not always considered in sufficient depth when analyzing experimental data. The present work discusses the chemical aspects of azocompounds as generators of peroxyl (and other) radicals, together with their contribution to our understanding of biochemistry, pharmaceutical and food chemistry research. The evidence supporting a role for the formation of alkoxyl (RO•) and other radicals during thermal and photochemical decomposition of azocompounds is assessed, together with the potential influence of such species on the reactions under study.

Physicochemical and Structural Characteristics of Soybean Protein Isolates Induced by Lipoxygenase-Catalyzed Linoleic Acid Oxidation during In Vitro Gastric Digestion

The effects of oxidation on the gastric digestion properties of soybean protein isolates (SPIs) in a model of lipoxygenase (LOX)-catalyzed linoleic acid (LA) oxidation system and the multiscale structural characterization of SPI hydrolysate were investigated. Results indicated that the feature of SPI hydrolysate is dependent upon the degree of oxidation. Pepsin hydrolysis caused a red shift in fluorescence intensity and a reduction in surface hydrophobicity and diminished the particle size of SPI hydrolysate during gastric digestion. Compared with the control, mild oxidation was beneficial to protein unfolding and gastric digestibility, as manifested by minimal molecular weight (MW) distribution >50 kDa (32.34%) and smaller peptide fragments under scanning electron microscopy. However, severe oxidation brought about 39.47% loss of free amino acids. It was interesting to find that glycinin was more vulnerable to pepsin hydrolysis after oxidation as compared to the native SPI. Overall, the moderately oxidized SPI appeared to be digested to a greater extent.