Structural and emulsifying properties of soybean protein isolate glycated with glucose based on pH treatment

Mechanism study on the improvement of egg white emulsifying characteristic by ultrasound synergized citral: Physicochemical properties, molecular flexibility, protein structure

As a natural emulsifier, egg white protein (EWP) has great interfacial characteristics and high security, and has broad development prospects. This study explored the impact of ultrasound synergized citral (CI) treatment on the microstructure, molecular flexibility and emulsifying property of EWP, and predicted the interaction between CI and ovalbumin (the main protein in EWP) through molecular docking. The decrease in free amino content and the growth in molecular weight of EWP suggested that CI and proteins were successfully grafted. The results of physicochemical properties revealed that UCEWP (ultrasound synergized citral-treated EWP) had smaller particle size and larger ζ-potential absolute value, which meant that the stability of UCEWP system was enhanced. From the perspective of interfacial characteristics, UCEWP had lower interfacial tension, which remarkably improved its emulsifying property. The emulsifying activity index (EAI) and emulsifying stability index (ESI) of UCEWP were 1.99 times and 3.19 times higher than that of natural EWP (NEWP). Analysis of Fourier transform infrared spectroscopy (FT-IR) and fluorescence spectroscopy illustrated that the secondary and tertiary structures of UCEWP were more disordered and stretched than those of EWPs. Protein microstructure demonstrated that UCEWP presented loose small particle distribution, and correlation analysis reflected that the improvement of molecular flexibility was positively correlated with the enhancement of emulsifying property. These results elucidated that ultrasound synergized CI treatment is an effective mean to improve the molecular flexibility and emulsifying property of EWP, which provides a valuable reference for further application of EWP.

Enhancing the Stability of Litsea Cubeba Essential Oil Emulsions Through Glycosylation of Fish Skin Gelatin via Dry Maillard Reaction

Emulsions are widely utilized in food systems but often face stability challenges due to environmental stresses, such as pH, ionic strength, and temperature fluctuations. Fish skin gelatin (FSG), a promising natural emulsifier, suffers from limited functional properties, restricting its broader application. This study explored the enhancement of emulsion stability in Litsea cubeba essential oil systems through the glycosylation of fish skin gelatin (FSG) with dextran via the dry Maillard reaction. Among dextrans of varying molecular weights (10 kDa, 100 kDa, 200 kDa, and 500 kDa), the 200 kDa dextran exhibited the best emulsification performance, achieving a remarkable 160.49% increase in stability index. The degree of grafting (DG) increased with molecular weight, peaking at 34.77% for the 500 kDa dextran, followed by 23.70% for the 200 kDa variant. The particle size of the FSG-Dex 200 kDa conjugate emulsion was reduced to 639.1 nm, compared to 1009-1146 nm for the unmodified FSG, while hydrophobicity improved by 100.56%. The zeta potential values approached 30 mV, indicating enhanced stability. Furthermore, glycosylation significantly improved antioxidant activity, as evidenced by increased radical scavenging capacity in both DPPH and ABTS assays. These findings underscore the potential of glycosylated FSG as a natural emulsifier in food applications.

Ultrasonic Treatment of Soybean Protein Isolate: Unveiling the Mechanisms for Gel Functional Improvement and Application in Chiba Tofu

Soybean protein isolate (SPI) cannot meet the needs of modern food production due to various shortcomings. By change of its structural characteristics, its application in the food field may be increased. This study explored the impact of ultrasonic treatment on the structural and gelation properties of the SPI dispersions. By subjecting SPI to ultrasonic treatment at 0-800 W for 10 min, it was found that this treatment significantly reduced the particle size of SPI to 196 nm and caused an increase in its solubility, surface hydrophobicity, and sulfhydryl content as well as significant changes in the protein structure. At an optimal ultrasonic power of 200 W, SPI gels demonstrated an enhanced gelling ability, strength, and water-holding capacity, forming a more uniform and compact structure. Application in Chiba tofu showed that water retention, elasticity, and sensory quality were optimized at 200 W. The findings highlight that a sonication power of 200 W significantly improves the physicochemical and structural properties of SPI, resulting in a denser and more functional gel suitable for Chiba tofu production.

Thermal-induced interactions between soy protein isolate and malondialdehyde: Effects on protein digestibility, structure, and formation of advanced lipoxidation end products

Thermally processed lipid- and protein-rich foods have sparked widespread concern since they may degrade food nutrition and even risk food safety. This study investigated soy protein isolate (SPI) alterations of digestibility and structure, as well as the formation of potentially hazardous chemicals, i.e., advanced lipoxidation end products (ALEs), after interacting with malondialdehyde (MDA, a lipid oxidation product) under high-temperature cooking conditions (100-180 °C, up to 60 min). In-vitro protein digestion of the SPI-MDA mixtures suggested that their room-temperature interactions damaged SPI digestibility, and increasing the temperature and the duration of the thermal treatment exacerbated the adverse effects. Protein oxidation, covalent aggregation of subunits, and changes in secondary and tertiary structures were revealed using thiol quantification, gel electrophoresis, fluorescence spectroscopy, and circular dichroism (CD) spectra, which could explain reduced protein digestibility. High-resolution mass spectrometry (HRMS) identified seven non-crosslinked ALEs and two crosslinked ALEs. Increased MDA concentrations promoted the generation of ALEs. Moreover, the acrolein-derived ALEs with reactive carbonyl groups were prone to further reacting into crosslinked ALEs, potentially responsible for the subunit aggregation.

Structural and functional properties of whey protein isolate-inulin conjugates prepared with ultrasound or wet heating method

BACKGROUND

Whey protein isolate (WPI) generally represents poor functional properties such as thermal stability, emulsifying activity and antioxidant activity near its isoelectric point or high temperatures, which limit its application in the food industry. The preparation of WPI-polysaccharide covalent conjugates based on Maillard reaction is a promising method to improve the physical and chemical stability and functional properties of WPI. In this research, WPI-inulin conjugates were prepared through wet heating method and ultrasound method and their structural and functional properties were examined.

RESULTS

In conjugates, the free amino acid content was reduced, the high molecular bands were emerged at sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), new C-N bonds were formed in Fourier-transform infrared (FTIR) spectroscopy, and fluorescence intensity was reduced compared with WPI. Furthermore, the result of circular dichroism (CD) spectroscopy also showed that the secondary structure of conjugates was changed. Conjugates with ultrasound treatment had better structural properties compared with those prepared by wet heating treatment. The functional properties such as thermal stability, emulsifying activity index (EAI), emulsion stability (ES) and antioxidant activity of conjugates with wet heating treatment were significantly improved compared with WPI. The EAI and ES of conjugates with ultrasound treatment were the highest, but the thermal stability and antioxidant activity were only close to that of the conjugates with wet heating treatment for 2 h.

CONCLUSION

This study revealed that WPI-inulin conjugates prepared with ultrasound or wet heating method not only changed the structural characteristics of WPI but also could promote its functional properties including thermal stability, EAI, ES and antioxidant activity. © 2024 Society of Chemical Industry.

Enhancing the functionality of pea proteins by conjugation with propylene glycol alginate via transacylation reaction assisted with ultrasonication

Pea proteins lack the desirable functional characteristics for food and beverage applications. In this study, transacylation reaction assisted with ultrasonication was used to glycate pea proteins with propylene glycol alginate to enhance their functional properties. The reaction was carried out at pH 11.0 for different pea protein isolate: propylene glycol alginate mass ratios and time durations in a sonic bath at 40 °C. Glycation was confirmed in gel electrophoresis, and ultrasonication enhanced the glycation, with optimal degrees of glycation observed at 45 min reaction time and mass ratios of 2:1 (37.73%) and 1:1 (35.96%). The transacylation reaction increased random coil content of pea proteins by 28% and enhanced their solubility by 2.02 times at pH 7.0, water holding capacity by >50% at pH 7.0, foaming properties, emulsifying properties, and heat stability. This study offers a novel approach that can enhance functionality and applicability of pea proteins.

Effect of glycosylation modification on structure and properties of soy protein isolate: A review

Soybean protein isolate (SPI) is a highly functional protein source used in various food applications, such as emulsion, gelatin, and food packaging. However, its commercial application may be limited due to its poor mechanical properties, barrier properties, and high water sensitivity. Studies have shown that modifying SPI through glycosylation can enhance its functional properties and biological activities, resulting in better application performance. This paper reviews the recent studies on glycosylation modification of SPI, including its quantification method, structural improvements, and enhancement of its functional properties, such as solubility, gelation, emulsifying, and foaming. The review also discusses how glycosylation affects the bioactivity of SPI, such as its antioxidant and antibacterial activity. This review aims to provide a reference for further research on glycosylation modification and lay a foundation for applying SPI in various fields.

Freeze-thaw stability of transglutaminase-induced soy protein-maltose emulsion gel: Focusing on morphology, texture properties, and rheological characteristics

In this study, soy protein isolate (SPI) and maltose (M) were employed as materials for the synthesis of a covalent compound denoted as SPI-M. The emulsion gel was prepared by transglutaminase (TGase) as catalyst, and its freeze-thaw stability was investigated. The occurrence of Maillard reaction was substantiated through SDS-PAGE. The analysis of spectroscopy showed that the structure of the modified protein was more stretched, changed in the direction of freeze-thaw stability. After three freeze-thaw cycles (FTC), it was observed that the water holding capacity of SPI-M, SPI/M mixture (SPI+M) and SPI emulsion gels exhibited reductions of 8.49 %, 16.85 %, and 20.26 %, respectively. Moreover, the soluble protein content also diminished by 13.92 %, 23.43 %, and 35.31 %, respectively. In comparison to unmodified SPI, SPI-M exhibited increase in gel hardness by 160 %, while elasticity, viscosity, chewability, and cohesion demonstrated reductions of 17.7 %, 23.3 %, 33.3 %, and 6.76 %, respectively. Concurrently, the SPI-M emulsion gel exhibited the most rapid gel formation kinetics. After FTCs, the gel elastic modulus (G') and viscosity modulus (G″) of SPI-M emulsion were the largest. DSC analysis underscored the more compact structure and heightened thermal stability of the SPI-M emulsion gel. SEM demonstrated that the SPI-M emulsion gel suffered the least damage following FTCs.

Dynamic microfluidic-assisted transglutaminase modification of soy protein isolate-chitosan: Effects on structural and functional properties of the adduct and its antioxidant activity after in vitro digestion

In this study, soy protein isolate (SPI)-chitosan (CS) adducts were prepared by using dynamic microfluidic-assisted transglutaminase (TGase) modification. It was shown that the solubility and degree of binding of SPI-CS adducts prepared by dynamic microfluidic-assisted TGase modification were better. After the samples were treated twice at 400 bar, the degree of binding for SPI-CS adducts increased to 31.97 ± 1.31%, and the solubility increased to 66.25 ± 1.10%. With the increase of microfluidic pressure, the exposed free sulfhydryl groups increased, the particle size reduced, and the surface hydrophobicity first increased and then decreased. Under the action of the pressure generated by microfluidics, the structure of the protein in the SPI-CS adduct was unfolded and transformed from an ordered structure to a disordered one. The SPI-CS adducts prepared with assisted dynamic microfluidic treatment showed significantly higher ABTS radical scavenging rate, DPPH radical scavenging rate and reducing power after in vitro digestion compared with that of SPI-CS adducts prepared with TGase alone. This result indicated that appropriate dynamic microfluidic treatment improved the structural and functional properties of TGase-modified SPI-CS adducts and significantly increased the antioxidant activity after in vitro digestion.

Effect of High-Intensity Ultrasound Pretreatment on the Properties of the Transglutaminase (TGase)-Induced β-Conglycinin (7S) Gel

In this study, we investigated the effects of different high-intensity ultrasound (HIU) pretreatment times (0-60 min) on the structure of β-conglycinin (7S) and the structural and functional properties of 7S gels induced by transglutaminase (TGase). Analysis of 7S conformation revealed that 30 min HIU pretreatment significantly induced the unfolding of the 7S structure, with the smallest particle size (97.59 nm), the highest surface hydrophobicity (51.42), and the lowering and raising of the content of the α-helix and β-sheet, respectively. Gel solubility showed that HIU facilitated the formation of ε-(γ-glutamyl)lysine isopeptide bonds, which maintain the stability and integrity of the gel network. The SEM revealed that the three-dimensional network structure of the gel at 30 min exhibited filamentous and homogeneous properties. Among them, the gel strength and water-holding capacity were approximately 1.54 and 1.23 times higher than those of the untreated 7S gels, respectively. The 7S gel obtained the highest thermal denaturation temperature (89.39 °C), G', and G″, and the lowest tan δ. Correlation analysis demonstrated that the gel functional properties were negatively correlated with particle size and the α-helix, while positively with Ho and β-sheet. By contrast, gels without sonication or with excessive pretreatment showed a large pore size and inhomogeneous gel network, and poor properties. These results will provide a theoretical basis for the optimization of HIU pretreatment conditions during TGase-induced 7S gel formation, to improve gelling properties.

Development of fish gelatin-chitooligosaccharide conjugates through the Maillard reaction for the encapsulation of curcumin

The poor water solubility, bioavailability and stability of bioactive compounds have become the bottleneck restricting their wide application, thus developing a functional carrier to realize the efficient encapsulation and activity improvement of active hydrophobic substances has become a research hotspot. In this work, a functional glycosylated fish gelatin (called FG-COS conjugates) carrier based on fish gelatin (FG) and chitooligosaccharide (COS) via Maillard reaction was developed. The functional carrier exhibited good antioxidant activity and high encapsulation of curcumin (Cur). Enhanced antioxidant effect of Cur loaded in FG-COS conjugates (called FG-COS-Cur nanoparticles) was achieved, showing remarkable UV protection on Cur and enhanced intracellular antioxidant activity of FG-COS-Cur nanoparticles. Remarkably, FG-COS-Cur nanoparticles increased the cell viability of H2O2-induced oxidative damage Caco-2 cells, drastically reduced the levels of reactive oxygen species (ROS) and lactate dehydrogenase (LDH), and significantly increased intracellular antioxidant enzyme activities, which all exhibited a dose-response relationship. These findings suggested that the FG-COS conjugates with intrinsic antioxidant activity could effectively encapsulate Cur and improved bioavailability for hydrophobic active molecules in functional food field.

Study on the binding behavior and functional properties of soybean protein isolate and β-carotene

This study focused on the non-covalent interaction between soybean protein isolate (SPI) and β-carotene (BC). The conformational changes of SPI with β-carotene in varying proportions (BC/SPI: 2%, 4%, 6%, 8%, and 10%) were investigated by multi-spectroscopy and molecular docking. Results showed that the quenching mode is static quenching and binding affinity increased with temperature. The stoichiometry was 1:1, indicating there was only one binding site in SPI. The binding was based on entropy and primarily driven by hydrophobic interactions and its binding constant was in the order of 104 L⋅mol–1. The addition of the β-carotene affected the secondary structure of SPI resulting in an increase in α-Helix and a decrease in random coil and β-turn content, indicating protein aggregated and hydrophobic interactions occurred. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) verified that no new larger molecular weight substance was formed and no covalent interaction existed. Molecular docking corroborated that electrostatic and hydrophobic interactions were both involved in the formation of complexes, where hydrophobic interaction was the dominant one. Moreover, β-carotene improved 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity, foaming capacity, and emulsifying stability of SPI. These findings provide useful information about the interaction mechanism of SPI and β-carotene, which contributes to the further development and application of SPI products rich in β-carotene in the food industry.