Application of ultrasound pretreatment and glycation in regulating the heat-induced amyloid-like aggregation of β-lactoglobulin

Structural characterization and emulsification properties of quinoa protein-dextran conjugates fabricated through ultrasound-assisted Maillard reaction

In this study, quinoa protein was grafted by dextran with varying molecular weights via the Maillard reaction, subjected to different ultrasound powers. Structural analysis revealed that dextran covalently bonded to the 11S globulin and B subunits of quinoa protein, causing the ordered structures transformed into β-turn and random coil. Among the conjugates, the one prepared with 40 kDa dextran at 200 W ultrasound power exhibited optimal modification effects, achieving a grafting degree of 28.6 %, a particle size of 91.01 nm, and a zeta potential of -39.3 mV. This conjugate had a low interfacial tension of 7.8 mN/m, attributed to its improved amphiphilic balance and enhanced steric stabilization. When applied to an oil-in-water system, the fabricated conjugate led to an emulsion with well-dispersed droplets and demonstrated excellent storage and creaming stability. Overall, this research advanced the functional utilization of quinoa protein, opening new avenues for its application as food material.

Investigating the fibrillation behavior of Spirulina platensis protein: Self-assembly process and effects on emulsion stability

Amyloid fibrils, characterized by their high aspect ratio and superior surface activity, present significat potential for stabilizing emulsion. This study investigated the effects of varying heating times on the structural transitions and emulsion stability of Spirulina platensis protein fibrils (SPPFs). SDS-PAGE analysis demonstrated that SPPFs formation was time-dependent. Atomic force microscopy (AFM) images showed a transition from spherical particles to fibrils. Thioflavin T (ThT) fluorescence, Nile red fluorescence, Congo red binding spectra, and FTIR spectroscopy indicated increased β-sheet content, reaching a maximum at 16 h. The ThT kinetics of SPPFs followed a pseudo-second-order model. Changes in intrinsic fluorescence and surface hydrophobicity were observed during fibril formation. Particle size and ζ-potential measurements confirmed enhanced dispersion stability at 16 h. Emulsions stabilized by SPPFs exhibited improved stability under alkaline conditions, low ionic strength, and thermal stress. These findings highlight the potential of SPPFs as effictive emulsifiers for emulsion-based food products.

Ultrasound-assisted heat treatment: Accelerating rice glutelin fibrils formation and enhancing emulsifying properties

The self-assembly of rice glutelin (RG) into RG fibrils (RGFs) represents a promising strategy for enhancing its functional properties. In this study, we investigated the effects of ultrasonic pretreatment on the fibrillation kinetics, structural characteristics, and functional properties of RGFs. The results indicated that ultrasonic pretreatment facilitated the unfolding of RG, resulting in an increased H0 and β-sheet, thereby accelerating the formation of RGFs and enhancing the fibril conversion rate. Thioflavin T fluorescence spectroscopic analysis confirmed the formation of numerous cross β-sheet structures following 4 h of heating; however, ultrasonic pretreatment reduced this duration to just 2 h. Additionally, the ζ-potential and solubility of RGFs were significantly improved following ultrasonic pretreatment. TEM revealed that the URG-6 fibril sample exhibited the smallest diameter (3.81-5.27 nm) and greatest length (1109.92-1946.21 nm), demonstrating a high aspect ratio. Furthermore, ultrasonic pretreatment enhanced the emulsifying properties of RGFs, with the URG-6 emulsion achieving the highest EAI (147.61 m2/g) and ESI (134.67 min), along with the smallest droplet sizes. This study provides the basis for the development of RGFs and broadens their application in the food industry.

Hemoglobin-derived amyloid fibrils: Fibrillization mechanisms and potential applications

Fibrils from food proteins were widely reported but it has not been reported on sus scrofa hemoglobin. Utilizing fibrillization strategies can efficiently utilize hemoglobin and reduce waste. This work explores a new strategy to prepare hemoglobin-derived fibrils by removing the heme group. Hydrophobic interaction was found to be a key factor in promoting the fibrillization process. Heme presence hindered the fibrillization process possibly by restricting the unfolding process due to its high hydrophobicity. The core sequences of fibrils were identified as HBA 30-36, HBA 96-110, HBA 126-139, HBB 15-41, HBB 104-117 and HBB 83-145, which are generally of high hydrophobicity and HSA (Hot spots of aggregation) scores. Fibrils exhibited excellent gel properties, water retention, iron-binding properties, and enhanced positive surface charge. These findings contribute to establishing a fibrillization mechanism of hemoglobin and highlight the possibility of hemoglobin-sourced fibrils in food industry.

Studies on the Efficient Extraction of Ovotransferrin and the Effect of Heating Treatment on Its Structure and Activity

Ovotransferrin (OVT) is very rich in nutritional value and possesses a variety of biological activities. However, there is a lack of suitable OVT extraction methods that are simple and suitable for large-scale production. For this reason, this study explored a new method of ovalbumin OVT extraction based on mesophilic treatment. The effects of different heat treatment conditions on the physicochemical properties and bioactivities of the prepared OVT and their influence mechanisms were investigated. The results showed that OVT could be efficiently extracted from egg white by moderate heat treatment. Based on single factor experiments, response surface methodology was used to determine the effects of heat treatment time, temperature and pH on the extraction rate of OVT. The yield was 93.65 ± 0.53% under the optimal extraction conditions (62.5 °C, 75 min, pH 8). SDS-PAGE and FT-IR showed that changes in the influencing factors during heating had different effects on OVT. In addition, different extraction parameters had different effects on the iron-binding and antioxidant capacities of OVT. This study provides a fast and efficient preparation method for OVT from egg white, which lays the foundation for the wide application of OVT.

Enhancement of physicochemical and techno-functional properties of soy protein isolate amyloid fibrils by moderate ultrasonic pretreatment

Plant protein can be functionally strengthened by its modification into amyloid fibrils, which has drawn growing interest. In this study, we investigated the effects of ultrasonic pretreatment on the fibrillation kinetics, physicochemical properties, and functional aspects of soy protein isolate amyloid fibrils (SPF). Firstly, soy protein isolates (SPI) were subjected to ultrasonic pretreatment by regulating time and power under neutral conditions. Subsequently, the pretreated SPI was converted into SPF through acidic heating. The results indicated that ultrasonic pretreatment significantly improved surface hydrophobicity and solubility of SPI through ultrasound's cavitation and thermal effects. Thioflavin T fluorescence assay revealed SPF40 (450 W, 40 min) had the fastest growth rate, 104.23 % higher than SPF0 (without ultrasonic pretreatment), while SPF10 (450 W, 10 min) had the highest fibril yield, 20.97 % higher than SPF0. Physicochemical analysis showed that ultrasonic pretreatment accelerated the formation of SPF from SPI by exposing the surface hydrophobic groups, lowering the zeta potential, breaking down original fibrils into shorter fibrils, and altering the secondary structure from α-helices into β-sheets. Morphological examination by transmission electron microscopy exhibited a higher maturation state, showing more rigid and straight fibrils structure in SPF10 compared to SPF0. Functionally, SPF with ultrasonic pretreatment had higher emulsifying activity than SPI and SPF0. Rheological analysis further confirmed SPF emulsions' better mechanical strength over SPI emulsions. Overall, this study demonstrates that ultrasonic pretreatment is an effective way to enhance the formation and properties of SPF, which can be further applied to developing advanced protein products and novel functional food systems.

Effects of molecular weight of hydrolysate on the formation of soy protein isolate hydrolysate nanofibrils: Kinetics, structures, and interactions

Enzymatic hydrolysis prior to protein fibrillation was an effective way to facilitate the formation of nanofibrils. This study aimed to investigate the effects of molecular weights of hydrolysate on the kinetics, structures, and interactions of soy protein isolate (SPI) hydrolysate nanofibrils. The results showed that hydrolysate with molecular weight > 10 kDa showed a distinct fibrillation kinetics curve and a higher apparent rate constant (27.72) during fibrillation, indicating their vital role in determining the fibrillation. Hydrolysate with molecular weight > 10 kDa could form nanofibrils with higher radius gyration (17.11 ± 0.77 Å) due to stronger hydrophobic interaction, showing a stronger fibrillation ability. Hydrolysate with molecular weight within 5-10 kDa exhibited enhanced π-π stacking interactions during fibrillation, thereby promoting the extension of nanofibrils, and contributing to the formation of more nanofibrils. Hydrolysate with molecular weight < 5 kDa tended to randomly aggregate during fibrillation, resulting in a significant loss of cross-β structures in nanofibrils. Therefore, hydrolysate with different molecular weights exhibited synergistic effects during fibrillation.

Effects of heat sterilization on protein physicochemical properties and release of metabolites of braised chicken after in vitro digestion

Heat sterilization enhances the safety and shelf-life of braised chicken, but its impact on protein digestibility and the release of metabolites remains unclear. Here, braised chicken was sterilized at 80 °C (LS), 100 °C (MS), and 121 °C (HS) for 30 min. Protein digestibility was assessed by in vitro digestion, whereas the release of metabolites was analysed by UPLC-QTOF-MS spectroscopy. Results revealed that LS had higher gastrointestinal digestibility (88.86 %) than MS (81.79 %) and HS (78.13 %). Increased carbonyl content, turbidity, particle size, and hydrophobicity, along with decreased sulfhydryl content and solubility, indicated rising protein oxidation aggregation with higher sterilization temperatures, explaining reduced digestibility. 96 metabolites were identified. Compared to the control group, LS exhibited a statistically significant variation in the biosynthesis of unsaturated fatty acids, MS displayed a significant difference in purine metabolism, and HS showed a significant difference in primary bile acid biosynthesis. Thus, LS is a promising sterilization method.

Pretreatment with low-frequency magnetic fields can improve the functional properties of pea globulin amyloid-like fibrils

Plant protein fibrils have recently attracted considerable attention due to their superior mechanical and interfacial properties. The objective of this study was to evaluate the feasibility of low-frequency magnetic field (LF-MF) pretreatment in enhancing the conversion and functional characteristics of the amyloid-like fibrils derived from pea globulin (PG), which was considered a sustainable hypoallergenic protein. The results showed that LF-MF-treated PG (MPG) assembled into longer amyloid-like fibrils compared with native PG (NPG). The MPG presented similar gelling, emulsifying, and foaming properties to the NPG, while the fibril samples exhibited significantly improved functional properties. Moreover, the amyloid-like fibrils generated from the MPG (MPGF) showed large aspect ratios accompanied by superior solubility, molecular flexibility, emulsion stability, and gelling properties. The improved functional properties of the amyloid-like fibrils generated from the MPG can provide a promising outlook for expanding the applications of the PG in food, medicine and other fields.

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.

Inhibition of water-diluted precipitate formation from egg whites by ultrasonic pretreatment: Insights from quantitative proteomics analysis

The formation of the egg white precipitate (EWP) during dilution poses challenges in food processing. In this paper, the effects of 90 W and 360 W ultrasonic intensities on the inhibition of EWP formation were investigated. The findings revealed that 360 W sonication effectively disrupted protein aggregates, decreasing the dry matter of EWP by 5.24 %, particle size by 57.86 %, and viscosity by 82.28 %. Furthermore, the ultrasonic pretreatment unfolded protein structures and increased the content of β-sheet structures. Combined with quantitative proteomics and intermolecular forces analysis, the mechanism by which ultrasonic pretreatment inhibited water-diluted EWP formation by altering protein interactions was proposed: ultrasonic pretreatment disrupted electrostatic interactions centered on lysozyme, as well as hydrogen-bonding interactions between ovomucin and water. In conclusion, our research provides valuable insights into the application of ultrasonic pretreatment as a means to control and improve the quality of egg white-based products.

Pulsed electric field enhances glucose glycation and emulsifying properties of bovine serum albumin: Focus on polarization and ionization effects at a high reaction temperature

Previous studies demonstrated that the non-thermal effects of pulsed electric fields can promote protein glycation below 40 °C, but it does not always enhance the emulsifying properties of proteins, such as in the bovine serum albumin/glucose model. Therefore, the aim of this study was to investigate the impact of non-thermal effects on the glucose glycation and emulsification properties of bovine serum albumin at 90 °C. The results of circular dichroism, surface hydrophobicity, and molecular dynamics simulations showed that the polarization effect increased the degree of glycation of bovine serum albumin-glucose conjugates from 12.82 % to 21.10 % by unfolding protein molecule, while the emulsifying stability index was increased from 79.17 to 100.73 compared with the control. Furthermore, the results of principal component analysis and Pearson correlation analysis indicated that the ionization effect and the free radicals generated by pulsed electric fields significantly (p < 0.05) inhibited browning and reduced free sulfhydryl content. This study demonstrated that pulsed electric fields combined with heating can prepare glycated proteins with good emulsifying properties in a short period of time and at temperatures lower than conventional heating while reducing energy consumption. This processing strategy has potential applications in improving the emulsifying performance of highly stable proteins.

Blueberry anthocyanins extract inhibits advanced glycation end-products (AGEs) production and AGEs-stimulated inflammation in RAW264.7 cells

BACKGROUND

Pharmacological interference is considered to be a successful approach to inhibit advanced glycation end-products (AGEs) production and to block AGEs-induced diseases. Some synthetic medicines are effective for inhibiting the glycation reaction, but they cannot be widely applied in clinical as a result of their side effects and security concerns. The present study uses blueberry anthocyanins extract (BAE) to attenuate AGEs formation and AGEs-induced inflammatory response in vitro.

RESULTS

In a bovine serum albumin-glucose model, BAE showed similar inhibitory activity on AGEs compared to the synthetic anti-glycation agent (aminoguanidine). The results showed that BAE exhibit strong anti-glycative action by scavenging glycosylated intermediates (Schiff base, fructosamine and α-dicarbonyl compounds), attenuating the molecular aggregation and amyloid-like fibrils formation, and preventing conformational modification. Additionally, BAE was found to dose-dependently inhibit the AGEs-induced secretions of nitric oxide and pro-inflammatory cytokines (interleukin-6, monocyte chemoattractant protein-1 and tumor necrosis factor-α) in RAW264.7 cells. The anti-inflammation activity of BAE was mediated by down-regulating the expressions of critical inflammatory markers, inducible nitric oxide synthase and cyclooxygenase-2, through nuclear factor-kappa B signaling pathways inhibition.

CONCLUSION

BAE could serve as a natural inhibitor for controlling AGEs and AGEs-induced chronic inflammation. © 2023 Society of Chemical Industry.

The changed structures of Cyperus esculentus protein decide its modified physicochemical characters: Effects of ball-milling, high pressure homogenization and cold plasma treatments on structural and functional properties of the protein

Three physical treatments, including ball-milling (BM), high pressure homogenization (HPH) and cold plasma (CP) were applied to modify structural and functional properties of Cyperus esculentus protein (CEP). The results showed that three treatments significantly altered morphology and reduced particle size of CEP. Both primary and secondary structures of CEP were hardly changed, while disulfide bonds and hydrophobic forces between amino acid residues of CEP were interrupted by three treatments, releasing free sulfhydryls and hydrophobic groups. With the free moiety accumulation, the reformed interactions between them enhanced the crystallinity and thermostability of CEP. Besides, solubility and emulsifying properties of CEP were significantly improved within a certain range of treatment duration and intensity, and three treatments decreased water but increased oil holding capacity of CEP. Conclusively, the modified physicochemical properties of CEP were decided by the changed molecular structures of CEP, and different treatments may satisfy different processing requirements for the protein.

Comprehensive binding analysis of glycated myosin with furan derivatives via glucose by means of multi-spectroscopy techniques and molecular docking simulation

Myosin is an ideal binding receptor for aroma compounds and its functional properties are easily affected by glucose. The study comprehensively clarified the effects of glucose glycation-induced structural modifications of myosin on its binding ability with furan derivatives, including 2-methylfuran, 2-furfural, and 2-furfurylthiol. The results demonstrated that the binding levels of furan derivatives were obviously affected by the glycation levels of myosin due to the changes of myosin structure and surface. The increased glycation levels caused the unfolding of myosin structure and accelerated the aggregation, as were exhibited by the data of zeta potential, particle size, microstructure, and secondary structure. The glycated myosin with wrinkled surfaces favored the significant increase of hydrophobic interactions (31.59-69.50 μg), the more exposure of amino acid residues (3459-6048), the formation of free sulfhydryl groups (16.37-20.58 mmol/104g) and hydrogen bonds. These key (non)covalent linkages accounted for the generation of glycated myosin-odorants complex, including 2-furfurylthiol (29.17-47.87 %), thus enhancing the resultant binding ability as evidenced by the free furan derivatives concentrations, fluorescence quenching and molecular docking simulation analysis. The glycated myosin for 8 h bound highest concentrations of furan derivatives. The results will provide comprehensive data on the retention of aroma compounds in meat products.

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.

Providing New Insights on the Molecular Properties and Thermal Stability of Ovotransferrin and Lactoferrin

Ovotransferrin (OVT) is a multi-functional protein showing over 50% homology with Bovine lactoferrin (BLF) and human lactoferrin (HLF), which have the potential to be a substitute for lactoferrin (LF) due to the limited production of LF. To explore the substitutability of OVT, the molecular properties and thermal stability of OVT, BLF and HLF were characterized because these properties will affect the processing quality and biological activities of protein products when exposed to different processing conditions (e.g., temperature, pH, ion strength). The results showed that although obviously different isoelectric point (5.31, 9.12 and 8.75 for OVT, BLF and HLF, respectively), particle size distribution and hydrophobicity were found, they exhibited good dispersity because of high potential value. They showed an endothermic peak at 80.64 °C, 65.71 °C and 90.01 °C, respectively, and the denaturation temperature varied at different pH and ionic strength. OVT and BLF were more susceptible to heating at pH 5.0 as reflected by the decline of denaturation temperature (21.78 °C shift for OVT and 5.81 °C shift for BLF), while HLF could remain stable. Compared with BLF, OVT showed higher secondary structure stability at pH 7.0 and 9.0 with heating. For example, the α-helix content of OVT changed from 20.35% to 15.4% at pH 7.0 after heating, while that of BLF changed from 20.05% to 6.65%. The increase on fluorescence intensity and redshifts on the maximum wavelength after heating indicated the changes of tertiary structure of them. The turbidity measurements showed that the thermal aggregation degree of OVT was lower than BLF and HLF at pH 7.0 (30.98%, 59.53% and 35.66%, respectively) and pH 9.0 (4.83%, 12.80% and 39.87%, respectively). This work demonstrated the similar molecular properties and comparable thermal stability of OVT to BLF and HLF, which can offer a useful reference for the substitute of LF by OVT.

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.

Improved water solubility of myofibrillar proteins by ultrasound combined with glycation: A study of myosin molecular behavior

The poor water solubility of myofibrillar proteins (MPs) limits their application in food industry, and is directly related to the molecular behavior associated with myosin assembly into filaments. This study aims to explore the effect of high-intensity ultrasound (HIU) combined with nonenzymatic glycation on the solubility, structural characteristics, and filament-forming behavior of MPs in low ionic strength media. The results showed that the HIU (200-400 W) application could promote the subsequent glycation reaction between MPs and dextran (DX) and interfere with the electrostatic balance between myosin rods, suppressing the formation of filamentous myosin polymers. Glycated MPs pretreated by 400 W HIU had the highest solubility, which corresponded to the smallest particle size, highest zeta potential, and optimum storage stability (P < 0.05). Structure analysis and microscopic morphology observations suggested that the loss of the MP superhelix and the depolymerization of filamentous polymers were the main mechanisms for MP solubilization. In conclusion, HIU combined with glycation can effectively improve the water solubility of MPs by destroying or suppressing the assembly of myosin molecules.

Effect of ultrasound on the glycosylation reaction of pea protein isolate-arabinose: Structure and emulsifying properties

This study investigated the effects of different ultrasonic power and ultrasonic time on the structure and emulsifying properties of pea protein isolate (PPI)-arabinose conjugates. An examination of the absorbance and color development of PPI-d-arabinose (Ara) conjugates found that compared with traditional heating, the degree of glycosylation of protein reached the maximum when the ultrasonic treatment power was 150 and the treatment time was 30 min. Structural analysis revealed that the content of disordered structures (β-turn and random coil) of the protein conjugates increased, the maximum emission wavelength of the fluorescence spectrum was red-shifted, and the UV second-order derivative values decreased. The protein structure unfolded, exposing more hydrophobic groups on the molecular surface. Ultrasonic treatment improved the emulsification of protein conjugates. The emulsifying activity index (EAI) increased to 19.7 and 19.3 m²/g, and the emulsifying stability index (ESI) also increased. The contact angle and zeta potential also demonstrate that ultrasonic power has a positive effect on emulsion stability. Based on examining the thermal stability of the emulsion, the ultrasonic treatment increased the thermal denaturation resistance of the protein. This result confirms that mild sonication can increase the degree of glycosylation reaction and improve the emulsification properties of protein-Ara conjugates, providing a theoretical basis for developing foods with excellent emulsification properties.

Modification of Ovalbumin by Maillard Reaction: Effect of Heating Temperature and Different Monosaccharides

Glycosylation is considered to be an effective way to improve the performance of protein emulsification. This study focused on the effects of the molecular structure and emulsifying properties of ovalbumin (OVA) by wet heating Maillard reaction with three types of monosaccharides (i.e., xylose, glucose, and galactose). Results showed that increasing reaction temperature from 55°C to 95°C could significantly improve the degree of grafting (DG), while glycosylated OVA conjugate with xylose at 95°C processed the highest DG of 28.46%. This reaction was further confirmed by the browning intensity determination. Analysis of Fourier transform infrared spectrophotometer, circular dichroism, and fluorescence spectra indicated that there were slight changes in the subunits and the conversion of α-helices to β-sheets, as well as the unfolded structures, thereby increasing the surface hydrophobicity and absolute zeta potential of obtained glycosylated OVA. Glycosylation endowed OVA with better emulsifying properties, especially the xylose glycosylated OVA was superior to that of glucose and galactose glycosylated OVA, which was mainly due to its shorter molecular chains with smaller steric hindrance for reaction. Furthermore, the enhancement of emulsifying properties may be attributed to the synergistic effect of stronger electrostatic repulsion of larger absolute zeta potential and the steric hindrance from thicker adsorbed layer, thereby inhibiting aggregation and flocculation of emulsion droplet.

Effect mechanism of ultrasound pretreatment on fibrillation Kinetics, physicochemical properties and structure characteristics of soy protein isolate nanofibrils

Self-assembly of soy proteins into nanofibrils is gradually considered as an effective method to improve their technical and functional properties. Ultrasound is a non-thermal, non-toxic and environmentally friendly technology that can modulate the formation of protein nanofibrils through controlled structural modification. In this research, the effect of ultrasound pretreatment on soy protein isolate nanofibrils (SPIN) was evaluated by fibrillation kinetics, physicochemical properties and structure characteristics. The results showed that the optimum ultrasound condition (20% amplitude, 15 min, 5 s on-time and 5 s off-time) could increase the formation rate of SPIN by 38.66%. Ultrasound reduced the average particle size of SPIN from 191.90 ± 5.40 nm to 151.83 ± 3.27 nm. Ultrasound could increase the surface hydrophobicity to 1547.67 in the initial stage of nanofibrils formation, and extend the duration of surface hydrophobicity increased, indicating ultrasound could expose more binding sites, creating more beneficial conditions for nanofibrils formation. Ultrasound could change the secondary and tertiary structure of SPIN. The reduction of α-helix content of ultrasound-pretreated soy protein isolate nanofibrils (USPIN) was 12.1% (versus 5.3% for SPIN) and the increase of β-sheet content was 5.9% (versus 3.5% for SPIN) during fibrillation. Ultrasound could accelerate the formation of SPIN by promoting the unfolding of SPI, exposure of hydrophobic groups and formation of β-sheets. Microscopic images revealed that USPIN generated a curlier and looser shape. And ultrasound reduced the zeta potential, free sulfhydryl groups content and viscosity of SPIN. SDS-PAGE results showed that ultrasound could promote the conversion of SPI into low molecular weight peptides, providing building blocks for the nanofibrils formation. The results indicated that ultrasound pretreatment could be a promising technology to accelerate SPIN formation and promote its application in food industry, but further research is needed for the improvement of the functional properties of SPIN.

Structural characteristics and emulsifying properties of myofibrillar protein-dextran conjugates induced by ultrasound Maillard reaction

In this study, we investigated the effect of the ultrasound-assisted Maillard reaction on the structural and emulsifying properties of myofibrillar protein (MP) and dextran (DX) conjugates with different molecular weights (40, 70 and 150 kDa). Compared with classical heating, mild and moderate ultrasound-assisted methods (100-200 W) could accelerate the later stage of the Maillard reaction, which increased the degree of graft (DG) and the content of advanced Maillard reaction products (MPRs). Structural analysis revealed conjugates obtained by Maillard reaction induced the loss of ordered secondary structures (α-helix, β-sheets) and red-shift of maximum emission wavelength of intrinsic fluorescence spectrum. The conjugate containing 40 kDa DX exhibited higher extent of Maillard reaction compared to those containing 70 kDa and 150 kDa DX under various treating methods. Moreover, the ultrasound-assisted Maillard reaction could effectively improve the emulsifying behaviors. 100 W ultrasound-induced conjugates grafted by 70 kDa DX produced the smallest emulsion size with optimum storage stability. Confocal laser scanning microscopy and analytical centrifugal analyzer further confirmed MP grafted by 70 kDa DX with the assistance of 100 W ultrasound field could produce the smallest and most homogeneous MP-base emulsion with no flocculation. Our study demonstrated that mild ultrasound treatment resulted in well-controlled Maillard reaction, and the related glycoconjugate grafted with 70 kDa DX showed the greatest improvements in emulsifying ability and stability. These findings provided a theoretical foundation for the development of emulsion-based foods with excellent characteristics.

Ultrasonic pretreatment enhanced the glycation of ovotransferrin and improved its antibacterial activity

This study aims to evaluate the effect of ultrasonic pretreatment combined with glycation on the structural characteristics and antibacterial activity of ovotransferrin (OVT). Firstly, OVT (purity >90%) was isolated from egg white with a simple and efficient method. After the treatment of ultrasound and glycation, the browning degree of OVT increased with the rising power of ultrasound, while the number of free amino groups obviously decreased to 25.4%. Various spectrum detection showed that the structures of OVT have changed significantly, indicating the tertiary structure became more flexible and looser. The minimal inhibitory concentration of ultrasound glycated OVT were 25.0 and 32.1 μmol/L for E. coli and S. aureus, respectively. In summary, ultrasound-assisted glycation is an effective technique to improve the biological activity of OVT.

Glycation from α-dicarbonyl compounds has different effects on the heat-induced aggregation of bovine serum albumin and β-casein

α-Dicarbonyl compounds are generated in large amounts during heat treatment in food production. This work compared the influence of glycation by α-dicarbonyl on the hydrothermal aggregation of bovine serum albumin (BSA) and of β-casein (β-CN). Glycation by α-dicarbonyl compounds was found to be more efficient than glycation by glucose in reducing the free amino groups, surface hydrophobicity and isoelectric point of BSA, thus greatly inhibited the hydrothermal aggregation of BSA. In addition, glycation by α-dicarbonyl greatly transformed the rigid BSA aggregates into flexible structures, based on analysis by fluorescence spectrum, transmission electron microscope and small-angle X-ray scattering. In contrast, both the aggregation process and aggregates conformation of β-CN were found to be minimally affected by glycation, possibly due to the intrinsic disorder of β-CN. This work highlights the substantial influences of α-dicarbonyl on dietary proteins during heat treatment depending on the protein structural characteristics.

Influence of salting process on the structure and in vitro digestibility of actomyosin

Salting process is widely used in the process of meat products, whereas few studies have revealed the digestibility of actomyosin after salting treatment, which is closely related with the nutrition of meat. This work reported effect of salting on the structural change and digestibility of actomyosin before and after heat treatment. Actomyosin in 0.4 M and 0.8 M of NaCl had higher content of disulfide bonds, and actomyosin in 0.4 M NaCl showed the largest particle sizes before and after heat treatment. In addition, actomyosin in 0.6 M and 0.8 M of NaCl was oxidized more severely after heat treatment. Based on peptidomics analysis by using liquid chromatography tandem mass spectrometry (LC-MS/MS), actomyosin in 0.6 M was digested more easily, which was followed by sample in 0.8 M and 0.4 M of NaCl in descending order. The lowest digestibility of actomyosin in 0.4 M NaCl was related with its higher content of disulfide bond and severer aggregation behavior. The lower digestibility of actomyosin in 0.8 M NaCl should be related with the higher content of disulfide bonds and surface oxidation. These results highlight the crucial role of salting process in affecting the digestibility of meat protein.

Influence of ultrasound pretreatment on the subsequent glycation of dietary proteins

The influence of ultrasound treatment on the subsequent glycation process of proteins is controversial. Glycation behaviors of bovine serum albumin (BSA), β-lactoglobulin (β-Lg) and β-casein (β-CN) after ultrasound pretreatment (UP) were compared by both evaluating glycation kinetics and analyzing structural changes of proteins. UP resulted in both unfolding and aggregation behavior in protein samples, which altered the accessibility of the Lys and Arg. Five cycles of UP up-regulated the glycation degree of BSA and β-Lg, possibly due to the unfolding behavior induced by UP, which exposed additional glycation sites. In contrast, 30 cycles of UP induced a dramatic increase (by 97.9 nm) in particle size of BSA, thus burying portions of glycation sites and suppressing the glycation process. Notably, UP had minimal influence on glycation kinetics of β-CN, due to its intrinsic disordered structure. Based on proteomics analysis, the preference of Lys and Arg during glycation was found to be changed by UP in BSA and β-Lg. Four, 3 and 3 unique carboxyethylated lysine residues were identified in glycated BSA after 0, 5 and 30 cycles of UP, respectively. This study suggests that the protein glycation can be affected by UP, depending on the ultrasonication duration and native structure of the protein.

The Effect of Limited Proteolysis by Trypsin on the Formation of Soy Protein Isolate Nanofibrils

Nanofibril system constructed by protein self-assembly is widely used in the food industry because of purposive functional properties. Soy protein isolate nanofibrils (SPINs) were reported to form via heating at pH 2.0. In this research, the soy protein isolate (SPI) hydrolysate prepared by trypsin was used as a raw material for the formation of nanofibrils called soy protein isolate hydrolysate nanofibrils (SPIHNs). Microscopic images demonstrated the formation of two nanofibrils. Based on circular dichroism spectroscopy and Thioflavin T (ThT) fluorescence spectral, we concluded that β-sheet played an important role in SPIN and SPIHN’s structural composition. At the same time, the α-helix in SPI had not been destroyed, thereby favoring the formation of SPIHN. The surface hydrophobicity of SPIHN continued to increase during the heating process and reached the highest value when heating 8 h. SDS-PAGE analysis showed that peptides produced by enzyme-modified SPI affected the formation of SPIHN. These results proposed that enzymatic hydrolysis prior to acidic during fibrillation process affected the fibrillation of SPI, and the peptides formed by enzymatic hydrolysis were more efficient for the self-assembly process. This study will provide a theoretical basis for the future research of SPI nanofibril functionality.

Recent nano-, micro- and macrotechnological applications of ultrasonication in food-based systems

There is a neoteric and rising demand for nutritional and functional foods which behooves food processors to adopt processing techniques with optimal conservation of bioactive components in foods and with minimal pernicious impacts on the environment. Ultrasonication, a mechanochemical technique has proven to be an efficacious panacea to these concerns. In this review, an analytic exploration of recent researches and designs regarding ultrasound methodology and equipment on diverse food systems, technological scales, procedural parameters and outcomes of such experimentations optimally scrutinized. The relative effects of ultrasonication on food formulations, components and attributes such as nanoemulsions, nanocapsules, proteins, micronutrients, sensory and mechanical characteristics are evaluatively delineated. In food systems where ultrasonication was employed, it was found to have a remarkable effect on one or more quality parameters. This review is a supplementation to the pedagogical awareness to scholars on the suitability of ultrasonication for research procedures, and a call to industrial food brands on the adoption of this technique for the development of foods with optimally sustained nutrient profiles.

Development of a novel Maillard reaction-based time-temperature indicator for monitoring the fluorescent AGE content in reheated foods

Dietary advanced glycation end products (AGEs) are formed via the Maillard reaction in foods, especially in reheated foods, and can cause chronic diseases. In this study, a series of Maillard reaction-based time-temperature indicators (TTIs: TTI-1, TTI-2, and TTI-3) were developed with lysine and xylose for monitoring the dynamic formation of fluorescent AGEs in reheated foods. The discoloration kinetics of Maillard reaction-based TTIs and the dynamics of fluorescent AGE formation were explored. Formulas were derived to illustrate the relationship of the color change in the TTIs with time and temperature. The activation energies (E a values) for generating the TTIs were 96.17, 87.98, and 83.55 kJ mol-1, respectively. TTI-1 was the optimal indicator for instant soy milk powder because it showed the lowest activation energy difference in this study. The results show that this series of Maillard reaction-based TTIs can be used to monitor the AGE contents in various reheated foods.

Heat-induced amyloid-like aggregation of β-lactoglobulin affected by glycation by α-dicarbonyl compounds in a model study

BACKGROUND

α-Dicarbonyl compounds are widely generated in the Maillard reaction, caramelization and oil oxidation during heat treatment. These compounds can readily react with lysine and arginine residues of a protein, whereas the influence of these compounds on protein structure and quality has seldom been revealed. This study compared influence of glycation by glucose and α-dicarbonyl compounds on amyloid-like aggregation of β-lactoglobulin (β-LG), both fibrillation kinetics and conformation of aggregates were studied.

RESULTS

Compared with glycation by glucose, the glycation by α-dicarbonyl compounds resulted in faster reduction of free amino group, sulfydryl group, and the relative content of β-sheet secondary structure, according to the ultraviolet (UV) spectra or circular dichroism (CD) spectra results. Based on the analysis of fibrillation kinetics using thioflavin T (ThT) binding assay, the glycation by α-dicarbonyls were more efficient in suppressing the growth of fibrillar aggregates. In addition, glycation by α-dicarbonyl resulted in amorphous oligomers, which were compared with the amyloid-like aggregates in control and glucose-glycated samples, based on the transmission electron microscopy (TEM) observation.

CONCLUSIONS

Glycation by α-dicarbonyl compounds induced larger decline in the β-sheet structure of β-LG than glycation by glucose, and thus largely suppressed the amyloid-like aggregation of β-LG and changed the morphology of aggregates. © 2019 Society of Chemical Industry.

The fate of dietary advanced glycation end products in the body: from oral intake to excretion

Advanced glycation end products (AGEs), which are closely associated with various chronic diseases, are formed through the Maillard reaction when aldehydes react with amines in heated foods or in living organisms. The fate of dietary AGEs after oral intake plays a crucial role in regulating the association between dietary AGEs and their biological effects. However, the complexity and diversity of dietary AGEs make their fate ambiguous. Glycated modifications can impair the digestion, transport and uptake of dietary AGEs. High and low molecular weight AGEs may exhibit individual differences in their distribution, metabolism and excretion. Approximately 50-60% of free AGEs are excreted after dietary intake, whereas protein-bound AGEs exhibit a limited excretion rate. In this article, we summarize several AGE classification criteria and their abundance in foods, and in the body. A standardized static in vitro digestion method is strongly recommended to obtain comparable results of AGE digestibility. Sophisticated hypotheses regarding the intestinal transportation and absorption of drugs, as well as calculated physicochemical parameters, are expected to alleviate the difficulties determining the digestion, transport and uptake of dietary AGEs. Orally supplied AGEs with low or high molecular weights must be supported by well-defined amounts in investigations of excretion. Furthermore, unequivocal evidence should be obtained regarding the degradation and metabolism products of dietary AGEs.

Effects of slit divergent ultrasound and enzymatic treatment on the structure and antioxidant activity of arrowhead protein

The arrowhead has attracted great research interest for their potential applications in pharmacy, food and biomedical areas. However, no information is reported about the nature and structure of the arrowhead protein (AP). Herein, effects of slit divergent ultrasound (28, 33, 40 KHz frequencies at 30-50 °C) and enzymatic (pepsin, trypsin, and alcalase) treatment on structure of AP were studied. In addition, changes in antioxidant activity of AP treated with ultrasound and enzymes were measured by chemical and cellular-based assays. The results showed that ultrasound treatment had considerable impact on the structure of AP and increased the susceptibility of AP to pepsin, trypsin and alcalase proteolysis. The changes in UV-Vis spectra, free sulfhydryl (SH) and disulfide bonds (SS) groups indicated that the structure of AP unfolded after ultrasound treatment. Besides, intrinsic fluorescence intensity of AP was increased by ultrasound treatment and then decreased after following enzymatic treatment. The circular dichroism (CD) analysis showed that ultrasound and enzymatic treatment decreased α-helix, β-turn of content of AP. However, the β-sheet and random coil content of AP increased. Interestingly, the AP after ultrasound and enzymatic treatment showed significant higher anti-oxidative activity in RAW 264.7 cells (p < 0.05) in comparison with control. In conclusion, the slit divergent ultrasonic provides a powerful endorsement for increasing the proteolysis of AP. Moreover, the improvement of the antioxidant activity of AP enzymatic hydrolysates provides a foundation of developing new type of plant-derived antioxidant peptides application.