Novel Protein Hydrocolloids Constructed by Hydrophobic Rice Proteins and Walnut Proteins as Loading Platforms for Nutraceutical Models

Properties of walnut protein-casein composites and their effects on the rheological behavior of high internal phase emulsions

The poor functional properties of walnut protein (WP) limit its application in food colloids. To address this issue, walnut protein-casein composites (WCCs) were fabricated using the pH-shift treatment featuring cost-effectiveness, high safety, and solvent-free nature. Both morphological and physiochemical analyses confirmed the nanoscale novel structures of WCCs. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) results demonstrated their structural integrity. The WCC structures were reshaped from more rigid α-helices and β-sheets to more flexible β-turns and random coils after complexation of WP with casein, as supported by circular dichroism spectral analysis. Moreover, fluorescence spectroscopy analysis of WCCs verified the contribution of electrostatic and hydrophobic interactions in maintaining WCC structures. The results of interfacial kinetics and interfacial rheology experiments found that WCCs with a WP/casein mass ratio of 1:1 (WCC-1:1) rapidly diffused, penetrated, and rearranged at the oil-water interface, forming a strong viscoelastic interfacial film. In addition, the high internal phase emulsion (HIPE) stabilized by WCC-1:1 (HIPE-1:1) exhibited optimal storage stability. Rheological experiments showed that HIPEs stabilized by WP, casein, and WCCs presented a gel network structure with viscoelastic behavior. HIPE-1:1 demonstrated notable viscosity, strain hardening, and structural reconstruction under large deformations. This study provides a strategy for manufacturing emulsion stabilizers based on heterologous dual proteins and insights for developing high-value WP products.

High internal phase Pickering emulsions stabilized by Pleurotus eryngii protein-polysaccharide conjugates

In this work, Pleurotus eryngii protein-polysaccharide conjugates (PE-PPCs) were used as the only stabilizer for the preparation of high internal phase emulsions (HIPEs). PE-PPCs presented spherical particles in solution, and their three-phase contact angle had a strong correlation with pH values, and the angle at pH 10.0 was almost 90°, showing the most balanced hydrophilicity and hydrophobicity. Subsequent tests had also confirmed that the emulsion prepared under this pH condition had the best performance. As expected, droplet size, apparent viscosity, and viscoelasticity of HIPEs stabilized by PE-PPCs were related to varying degrees with pH values, PE-PPC concentrations (c), and oil phase volume fraction (φ). Finally, the optimal conditions (pH 10.0, PE-PPCs concentration of 30 mg/mL, φ = 0.77) were obtained. Our findings in this study can be helpful for the preparation of food-grade HIPEs, and also have reference value in the field of studying the stability of protein-polysaccharide conjugates at the oil-water interface.

Food Gels Based on Polysaccharide and Protein: Preparation, Formation Mechanisms, and Delivery of Bioactive Substances

Hydrogels have a unique three-dimensional network that can create a good environment for the loading of functional compounds; hence, they have considerable potential in the delivery of bioactive substances. Natural macromolecular substances (proteins, polysaccharides) have the features of low toxicity, degradability, and biosafety; thus, they can be employed in the manufacture of hydrogels in the food sector. With its customizable viscoelastic and porous structure, hydrogels are believed to be good bioactive material delivery vehicles, which can effectively load polyphenols, vitamins, probiotics, and other active substances to prevent their influence from the external environment, thereby improving its stability. In this research, the common raw materials, preparation methods, and applications in the delivery of bioactive elements of food gels were examined; this study aimed at presenting new ideas for the development and utilization of protein-based food gels.

Investigating the impact of ultrasound-assisted treatment on the crafting of mulberry leaf protein and whey isolate complex: A comprehensive analysis of structure and functionality

Mulberry leaf protein (MLP) is a nutrient-rich protein, but its applicability is limited because of its poor solubility. To address this issue, this study combines MLP with whey protein isolates (WPI), known for the high nutritional value, and subsequently forms composite protein nanoparticles using the ultrasound-assisted pH shifting method. Microscopic observation and SDS-PAGE confirmed the binding between these two proteins. Fluorescence spectra and Fourier Transform infrared spectroscopy (FTIR) analysis supported the involvement of electrostatic interactions, hydrophobic attractions, and hydrogen bonding in the formation of stable complex nanoparticles. The interactions between the proteins became stronger after ultrasound-assisted pH-shifting treatment. Solubility, emulsification capacity, foaming, and antioxidant activity, among other indicators, demonstrate that the prepared composite nanoparticles exhibit favorable functional properties. The study successfully illustrates the creation of protein-based complex nanoparticles through the ultrasound-assisted pH shifting method, with potential applications in the delivery of bioactive compounds.

Preparation and Properties of Walnut Protein Isolate-Whey Protein Isolate Nanoparticles Stabilizing High Internal Phase Pickering Emulsions

To enhance the functional properties of walnut protein isolate (WalPI), hydrophilic whey protein isolate (WPI) was selected to formulate WalPI-WPI nanoparticles (nano-WalPI-WPI) via a pH cycling technique. These nano-WalPI-WPI particles were subsequently employed to stabilize high internal phase Pickering emulsions (HIPEs). By adjusting the mass ratio of WalPI to WPI from 9:1 to 1:1, the resultant nano-WalPI-WPI exhibited sizes ranging from 70.98 to 124.57 nm, with a polydispersity index of less than 0.326. When the mass ratio of WalPI to WPI was 7:3, there were significant enhancements in various functional properties: the solubility, denaturation peak temperature, emulsifying activity index, and emulsifying stability index increased by 6.09 times, 0.54 °C, 318.94 m2/g, and 552.95 min, respectively, and the surface hydrophobicity decreased by 59.23%, compared with that of WalPI nanoparticles (nano-WalPI), with the best overall performance. The nano-WalPI-WPI were held together by hydrophobic interactions, hydrogen bonding, and electrostatic forces, which preserved the intact primary structure and improved resistance to structural changes during the neutralization process. The HIPEs stabilized by nano-WalPI-WPI exhibited an average droplet size of less than 30 μm, with droplets uniformly dispersed and maintaining an intact spherical structure, demonstrating superior storage stability. All HIPEs exhibited pseudoplastic behavior with good thixotropic properties. This study provides a theoretical foundation for enhancing the functional properties of hydrophobic proteins and introduces a novel approach for constructing emulsion systems stabilized by composite proteins as emulsifiers.

Research progress of protein complex systems and their application in food: A review

Among the common natural biomolecules, the excellent properties of proteins have attracted extensive attention from researchers for functional applications, however, in native form proteins have many limitations in the performance of their functional attribute. However, with the deepening of research, it has been found that the combination of natural active substances such as polyphenols, polysaccharides, etc. with protein molecules will make the composite system have stronger functional properties, while the utilization of pH-driven method, ultrasonic treatment, heat treatment, etc. not only provides a guarantee for the overall protein-based composite system, but also gives more possibilities to the protein-composite system. Protein composite systems are emerging in the fields of novel active packaging, functional factor delivery systems and gel systems with high medical value. The products of these protein composite systems usually have high functional properties, mainly due to the interaction of the remaining natural active substances with protein molecules, which can be broadly categorized into covalent interactions and non-covalent interactions, and which, despite the differences in these interactions, together constitute the cornerstone for the stability of protein composite systems and for in-depth research.

Solubilization mechanism of self-assembled walnut protein nanoparticles and curcumin encapsulation

BACKGROUND

Native walnut protein is an alkali-soluble protein that seriously limits the application of walnut protein. The pH-shifting method could improve the solubility of walnut proteins and enable the encapsulation of active ingredients. The present study aimed to prepare water-soluble nanoparticles of curcumin using walnut protein and evaluate the process of walnut protein self-assembly, interaction between walnut protein and curcumin, encapsulation properties, and stability of nanoparticles.

RESULTS

The solubility of native walnut protein was poor, but the solubility of walnut protein nanoparticles (WPNP) formed by walnut protein after pH-shifting significantly improved to 91.5 ± 1.2%. This is because, during the process of pH changing from 7 to 12 and back to 7, walnut protein first unfolded under alkaline conditions and then refolded under pH drive, finally forming an internal hydrophobic and external hydrophilic shell-core structures. The quenching type of walnut protein and curcumin was static quenching, and the quenching constant was 2.0 × 10¹⁴  mol^-1  L^-1  s^-1 , indicating that the interaction between walnut protein and curcumin was non-covalent. Adding curcumin resulted in the formation of nanoparticles with small particle size compared with the no-load. The loading capacity of curcumin-loaded walnut protein nanoparticles (WPNP-C) was 222 mg g^-1 walnut protein isolate. Under the same mass, the curcumin equivalent concentration in aqueous solution of WPNP-C was 17 000 times higher than that of the native curcumin.

CONCLUSION

The solubility of the self-assembled WPNP significantly increased after pH-shifting treatment. The walnut protein carrier could improve the stability of the encapsulated curcumin. Therefore, walnut proteins could be used as water-soluble carriers for hydrophobic drugs. © 2023 Society of Chemical Industry.

Walnut Protein: A Rising Source of High-Quality Protein and Its Updated Comprehensive Review

Recently, plant protein as a necessary nutrient source for human beings, a common ingredient of traditional processed food, and an important element of new functional food has gained prominence due to the increasing demand for healthy food. Walnut protein (WP) is obtained from walnut kernels and walnut oil-pressing waste and has better nutritional, functional, and essential amino acids in comparison with other vegetable and grain proteins. WP can be conveniently obtained by various extraction techniques, including alkali-soluble acid precipitation, salting-out, and ultrasonic-assisted extraction, among others. The functional properties of WP can be modified for desired purposes by using some novel methods, including free radical oxidation, enzymatic modification, high hydrostatic pressure, etc. Moreover, walnut peptides play an important biological role both in vitro and in vivo. The main activities of the walnut peptides are antihypertensive, antioxidant, learning improvement, and anticancer, among others. Furthermore, WP could be applied in the development of functional foods or dietary supplements, such as delivery systems and food additives, among others. This review summarizes recent knowledge on the nutritional, functional, and bioactive peptide aspects of WP and possible future products, providing a theoretical reference for the utilization and development of oil crop waste.

Modification and Solubility Enhancement of Rice Protein and Its Application in Food Processing: A Review

Rice protein is a high-quality plant-based protein source that is gluten-free, with high biological value and low allergenicity. However, the low solubility of rice protein not only affects its functional properties such as emulsification, gelling, and water-holding capacity but also greatly limits its applications in the food industry. Therefore, it is crucial to modify and improve the solubility of rice protein. In summary, this article discusses the underlying causes of the low solubility of rice protein, including the presence of high contents of hydrophobic amino acid residues, disulfide bonds, and intermolecular hydrogen bonds. Additionally, it covers the shortcomings of traditional modification methods and the latest compound improvement methods, compares various modification methods, and puts forward the best sustainable, economical, and environmentally friendly method. Finally, this article lists the uses of modified rice protein in dairy, meat, and baked goods, providing a reference for the extensive application of rice protein in the food industry.

Tuning the electrostatic interaction between rice protein and carboxymethyl cellulose toward hydrophilic composites with enhanced functional properties

Protein-polysaccharide interactions have attracted much attention due to inherent potential in generating new structures and functionalities. In the present study, by simply mixing rice proteins (RPs) with carboxymethyl cellulose (CMC) at pH 12.0 prior neutralization, novel protein-polysaccharide complexes (RCs) were structured with water dispersibility and functionalities highly dependent on the degree of substitution (DS) and molecular weight (Mw) of CMC. Specifically, the water-dispersibility of RPs was increased from 1.7 % to 93.5 % at a RPs/CMC mass ratio of 10:1 with CMC of DS1.2 (Mw = 250 kDa). Fluorescence and circular dichroism spectra showed suppressed folding tendency of RPs by CMC during neutralizing the basicity, indicating controllable protein conformations. Furthermore, the structures of RCs became more unfolded for CMC with a larger DS or a smaller Mw. This enabled RCs with highly controllable functionalities in terms of emulsifying and foaming properties, which may have promising applications in developing food matrix with customized structures and textures.

Ultra-thermostable soy protein particles fabricated by combining preheat treatment with slightly alkaline pH

The development of beverages with high protein concentrations has received considerable interests; nevertheless, the pasteurization process, which causes unwanted protein aggregation and gelation, is currently posing a significant obstacle. Herein,...

Plant-based high internal phase emulsions stabilized by dual protein nanostructures with heat and freeze-thaw tolerance

The formation of coherent, three-dimensional (3D) networks by particles either at the interface or in the bulk phase is vital for the stability of emulsions. In this study, nanoparticles of walnut proteins (WPs) were associated by unfolded fibrillar rice proteins (RPs), forming dual protein nanostructures (DPNs) characteristic of coherent 3D networks. The DPNs emulsified walnut oil and formed high internal phase emulsions (HIPEs), which were stable against 2-month storage and 30-min heating at 95 °C. Furthermore, the interfacial structures can be further reinforced by sodium chloride (50 mM and above), and became invulnerable to repeated freeze-thaw treatments. Based on the above results, a plant-based walnut sauce was developed with superior freeze-thaw stability to three arbitrary commercial mayonnaises. The HIPEs with tunable rheological properties in response to salt concentration and excellent stabilities against long-term storage, heating, and freeze-thaw may be potential surrogates of futuristic plant-based textural and sensory materials in foods.