Maillard Conjugation of Sodium Alginate to Whey Protein for Enhanced Resistance to Surfactant-Induced Competitive Displacement from Air-Water Interfaces

Effects of Conjugation with Basil Seed Gum on Physicochemical, Functional, Foaming, and Emulsifying Properties of Albumin, Whey Protein Isolate and Soy Protein Isolate

Protein conjugation with the Maillard reaction has received considerable attention in the past decades in terms of improving functional properties. This study evaluated the changes in the techno-functional properties of whey protein isolate (WPI), soy protein isolate (SPI), and albumin (Alb) after conjugation with basil seed gum (BSG). The conjugates were developed via the Maillard reaction. Various analyses including FT-IR, XRD, SEM, SDS-PAGE, DSC, RVA, rheology, zeta potential, emulsion, and foaming ability were used for evaluating conjugation products. Conjugation between proteins (WPI, SPI, Alb) and BSG was validated by FT-IR spectroscopy. XRD results revealed a decrease in the peak of BSG after conjugation with proteins. SDS-PAGE demonstrated the conjugation of WPI, SPI, and Alb with BSG. DSC results showed that conjugation with BSG reduced the Tg of WPI, SPI, and Alb from 210.21, 207.21, and 210.90 °C to 190.30, 192.91, and 196.66 °C, respectively. The emulsion activity and emulsion stability of protein/BSG conjugates were increased significantly. The droplet size of emulsion samples ranged from 112.1 to 239.3 nm on day 3. Nanoemulsions stabilized by Alb/BSG conjugate had the smallest droplet sizes (112.1 and 143.3 nm after 3 and 17 days, respectively). The foaming capacity of WPI (78.57%), SPI (61.91%), and Alb (71.43%) in their mixtures with BSG increased to 107.14%, 85.71%, and 85.71%, respectively, after making conjugates with BSG. The foam stability of WPI (39.34%), SPI (61.57%), and Alb (53.37%) in their mixtures with BSG (non-conjugated condition) increased to 77.86%, 77.91%, and 72.32%, respectively, after formation of conjugates with BSG. Conjugation of BSG to proteins can improve the BSG applications as a multifunctional stabilizer in pharmaceutical and food industries.

Alleviation effect of lutein Pickering emulsion formed by casein-dextran conjugates through Maillard reaction against blue light retinal degeneration

With the increasing prevalence of electronic devices, awareness of the risks linked to blue light exposure has significantly heightened. Lutein, a powerful antioxidant, safeguards eye tissue by filtering blue light, while supplementation with docosahexaenoic acid (DHA) enhances retinal function. Adequate intake of these nutrients can help reduce the potential damage from prolonged blue light exposure. The protective effects of lutein and algal oil stabilized with Pickering emulsion were investigated using casein-dextran (CD) conjugates via Maillard reaction. Microstructural analysis revealed a three-dimensional network structure surrounding oil droplets formed by CD conjugates. With the increase of the oil phase ratio from 55 % to 80 %, the average size of Pickering emulsion droplets decreased. Pickering emulsion demonstrated higher viscoelasticity, excellent recovery, thixotropy, and good thermal stability as the oil phase ratio increased. The retention of lutein in CD-75 % Pickering emulsions showed significant improvement under various conditions. Simulated gastrointestinal digestion demonstrated that CD-75 % Pickering emulsions effectively enhanced the lutein bioaccessibility from 19.97 % to 48.99 %. In vivo experiments showed that lutein-loaded Pickering emulsion could effectively relieve blue light-induced retinal degeneration in mice. These findings suggested that Pickering emulsion can serve as a delivery system to protect lutein, offering a nutritional intervention to mitigate blue light-induced retinal degeneration.

Aggregate Size Modulates the Oil/Water Interfacial Behavior of Myofibrillar Proteins: Toward the Thicker Interface Film and Disulfide Bond

Myofibrillar protein (MP) aggregate models have been established to elucidate the correlation between their aggregate sizes and interfacial properties. The interfacial layer thickness was measured by the polystyrene latex method and quartz crystal microbalance with dissipation measurement. Interfacial conformations were then characterized in situ (front-surface fluorescence spectroscopy) and ex situ (reactive sulfhydryl group and secondary structure measurement following MP displacement). The viscoelasticity of the interfacial film and its resistance to surfactant-induced competitive displacement were reflected by the dilatational rheology and dynamic interfacial tension with the bulk phase exchange. Finally, we compared the findings of competitive displacement before/after adding a sulfhydryl-blocking agent, N-ethylmaleimide, to highlight the role of S-S linkage on interfacial film formation and stability. We substantiated that the aggregate size of the MP governed their interfacial properties. Small-sized aggregates exhibited more ordered secondary structures on the oil-water interface, which was conducive to the adsorption ratio of the protein and the adsorption dynamics. Although larger aggregates lowered the diffusion rate during interfacial film formation, they allowed the thicker and more viscoelastic interfacial film to be constructed afterward through more disulfide bond formation, resulting in greater resistance to surfactant-induced competitive displacement.

Impact of Phenolic Acid Derivatives on β-Lactoglobulin Stabilized Oil-Water-Interfaces

The physical stability of protein-based emulsions depends on intra- and intermolecular interactions of the interfacial protein-film. As studied in aqueous systems before, phenolic acid derivatives (PADs) non-covalently or covalently crosslink proteins depending on pH-value and thus, may impact interfacial protein-films. Whether these interactions occur in the same manner at the interface as in water and how they vary the properties of the interfacial protein-film has not been clarified. The present study aimed to investigate the interfacial protein-film viscoelasticity and physical emulsion-stability after non-covalently (pH 6.0) and covalently (pH 9.0) crosslinking depending on PAD-structure. For this purpose, we studied an interfacial β-lactoglobulin film with dilatational rheology after crosslinking with PADs, varying in number of π-electrons and polar substituents. Then, we analyzed the physical emulsion-stability by visual evaluation and particle size distribution. The results indicate that PADs with a high number of π-electrons (rosmarinic acid and chicoric acid) weaken the protein-film due to competing of phenol-protein interactions with protein-protein interactions. This is reflected in a decrease in interfacial elasticity. PADs with an additional polar substituent (verbascoside and cynarine) seem to further weaken the protein film, since the affinity of the PADs to the interface increases, PADs preferentially adsorb and sterically hinder protein-protein interactions. In emulsions at pH 6.0 and thus low electrostatic repulsion, PADs promote bridging-flocculation. Due to higher electrostatic repulsion at pH 9.0, the PADs are sterically hindered to form bridges, even though they are polymeric. Hence, our research enables the control of protein-film viscoelasticity and emulsion-stability depending on the PAD-structure.

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Soy Protein Isolate/Sodium Alginate Microparticles under Different pH Conditions: Formation Mechanism and Physicochemical Properties

The effects of sodium alginate (SA) and pH value on the formation, structural properties, microscopic morphology, and physicochemical properties of soybean protein isolate (SPI)/SA microparticles were investigated. The results of ζ-potential and free sulfhydryl (SH) content showed electrostatic interactions between SPI and SA, which promoted the conversion of free SH into disulfide bonds within the protein. The surface hydrophobicity, fluorescence spectra, and Fourier transform infrared spectroscopy data suggested that the secondary structure and microenvironment of the internal hydrophobic groups of the protein in the SPI/SA microparticles were changed. Compared with SPI microparticles, the surface of SPI/SA microparticles was smoother, the degree of collapse was reduced, and the thermal stability was improved. In addition, under the condition of pH 9.0, the average particle size of SPI/SA microparticles was only 15.92 ± 0.66 μm, and the distribution was uniform. Rheological tests indicated that SA significantly increased the apparent viscosity of SPI/SA microparticles at pH 9.0. The maximum protein solubility (67.32%), foaming ability (91.53 ± 1.12%), and emulsion activity (200.29 ± 3.38 m²/g) of SPI/SA microparticles occurred at pH 9.0. The application of SPI/SA microparticles as ingredients in high-protein foods is expected to be of great significance in the food industry.

Effect of Fructus Mori. bioactive polysaccharide conjugation on improving functional and antioxidant activity of whey protein

Whey protein with high biological and technological values is an excellent source of nutrition. However, the limited functional properties prevent its widespread applications in food industry. In this study, the whey protein functionality was improved via glycation with mulberry fruit polysaccharide by Maillard reaction. The sodium dodecyl sulfate-polyacrylamide gel electrophoresis profile and free amino groups determination confirmed the glycation occurred between whey protein and mulberry fruit polysaccharide. The emulsion capacity and stability of the conjugates were 1.40-fold and 1.52-fold higher than that of whey protein. The conjugates also exhibited remarkably improved antioxidant activity. The fish oil emulsion coated by conjugates demonstrated smaller droplet size, better storage and oxidative stability than that stabilized by whey protein. The findings would be of vital importance for updated understanding of the modification in emulsifying properties of proteins by glycation with natural bioactive polysaccharides as well as for the development of healthy foods.

Surfactant-Induced Competitive Displacement of Potato Pectin-Protein Conjugate from the Air-Water Interface

Potato pectin contains some proteinaceous components and exhibits emulsifying and emulsion stabilizing abilities. The objective of this study was to elucidate the effect of the pectin moiety of the pectin-protein conjugate present in pectic extracts from potato tubers on their interfacial properties. Potato pectin was extracted from highly purified cell wall materials to avoid the contamination of unconjugated proteins. The abilities of the potato pectin to adsorb to graphite surfaces and to resist surfactant-induced competitive displacement from the air-water interface were investigated using atomic force microscopy. The pectin moiety of the potato pectin was capable of adsorbing to graphite surfaces even after alkali treatment. Furthermore, the potato pectin exhibited enhanced resistance to surfactant-induced competitive displacement from the interface as a result of the formation of network structures of self-assembled pectin moieties at the interface. The present results suggest the importance of the pectin moiety with regard to the interfacial properties of potato pectin.