Combination of pH-shifting, ultrasound, and heat treatments to enhance solubility and emulsifying stability of rice protein isolate

Effects of ultrasound-induced structural modifications on the emulsifying properties of Tenebrio molitor proteins

Ultrasonication has emerged as a promising technique for modifying physicochemical properties of proteins, enhancing their functionality in food applications. This study evaluated the effects of ultrasonic treatment on the structural and functional properties of mealworm-derived proteins (MPs) and their potential as emulsifiers. Dynamic light scattering revealed a significant reduction in MP particle size from 3464.3 nm (untreated) to 115.5 nm (30 min sonication), along with increased zeta potential, indicating improved colloidal stability. Sonication enhanced oil-holding capacity and solubility, suggesting improved interfacial adsorption and emulsification. Circular dichroism and FT-IR spectroscopy confirmed structural modifications, including increased α-helix content and enhanced hydrogen bonding interactions. Free sulfhydryl content and surface hydrophobicity analyses indicated ultrasound-induced unfolding, exposing functional groups that contribute to emulsifying properties. Sonicated MPs demonstrated superior emulsion stability under varying temperature, pH, and ionic conditions. Furthermore, digestibility analysis showed improved gastric digestion (72.7 % to 82.8 %) and enhanced lipid digestion in the small intestine (36.2 % to 47.9 %), suggesting greater bioavailability. These physicochemical modifications highlight the feasibility of using sonicated MP as natural emulsifiers with enhanced functionality. This study underscores their potential in food formulations, particularly for nutritionally fortified emulsions, contributing to sustainable and functional food ingredient development.

Effect of pH-shifting combined with heat or ultrasonication treatment on physicochemical properties of quinoa protein isolates (QPI) dispersions

Quinoa protein isolate (QPI) offers a balanced amino acid profile but exhibits poor solubility, foaming, and emulsifying properties, limiting its broader use in food applications. This study evaluated the synergistic effects of pH-shifting (pH 2, 7, 10, and 12) combined with heat (50 °C) or sonication (20 kHz, 12.5 W, 30 min) on the structural and functional properties of QPI. The combination of pH-shifting at pH 12 with sonication achieved the highest solubility (~90 %), foaming capacity (~170 %), foaming stability (~45 %), and emulsifying performance (EAI: ~80 m2/g, ESI: ~35 min), outperforming either treatment alone. These enhancements were associated with reduced particle size (to ~40 nm), increased random coil content, and greater surface hydrophobicity, factors that improved protein flexibility and interfacial adsorption. Structural unfolding from extreme pH-shifting further amplified the effects of sonication through cavitation-induced disaggregation. This study demonstrates that combining alkaline pH-shifting with sonication is an effective strategy to improve QPI's technofunctional properties. The findings provide valuable insights for developing QPI as a functional, clean-label ingredient in plant-based emulsions, foams, and beverages. Future work should focus on interfacial characterization, sensory evaluation, and processing optimization to support industrial application.

Effect of Ultrasound Time on Structural and Gelling Properties of Pea, Lupin, and Rice Proteins

Plant proteins are garnering interest due to the growing demand for plant-based products, but their functionality in gel-based foods remains limited. Ultrasound (US) technology may improve the technological properties of proteins. Thus, the effect of US treatment time (0-15 min) on the structure and gelling properties of pea, lupin, and rice proteins was evaluated. The results showed that the whiteness (~60%) of all freeze-dried proteins remained unchanged (p > 0.05), regardless of the US time. However, FT-IR analysis revealed progressive reductions in α-helix and β-sheet for pea and lupin proteins (~50%) with US time, indicating partial unfolding. In addition, microstructure analysis showed an ~80% reduction in aggregate size for these proteins, while rice protein exhibited minimal changes. Conversely, weak gels were formed with pea and lupin proteins treated after 5 and 10 min of US, respectively, whereas rice protein did not form gels. Furthermore, US treatment time significantly increased (p < 0.05) the mechanical moduli, resulting in more structured gels after longer treatment times (tan δ ~0.3 at 15 min of US). These findings suggest that US treatment enhances the gelling properties of pea and lupin proteins, making them more suitable for plant-based food applications such as yogurt or desserts.

Structures and interactions of bamboo shoot protein-shellac complexes prepared by pH-driven method

A previous study showed that the by-product of square bamboo shoot processing was rich in protein and contained many essential amino acids good for health. Bamboo shoot protein (BSP) had great potential as a naturally occurring functional protein. However, the utilization of single plant protein is limited due to its unstable degradation and reduced bio-activity in the gastrointestinal tract. Improving the stability and functional properties of BSP by complexion with other natural polymers is a potential strategy. And shellac (SHL), as a natural polymer, has good pH responsiveness and thermal stability. In this study, bamboo shoot protein-shellac (BS) complexes of different mass ratios were prepared by pH-driven method, which showed that the covalent and non-covalent interactions between the two reduced the particle size. At the ratio of 2:1 (BS-2:1), the complex generated had the smallest size of 193.97 nm, PDI of <0.20, and ζ-potential of -27.99 mV, its solution had higher stability and higher thermal tolerance. FTIR and fluorescence intensity further demonstrated that the pH-driven method resulted in structural changes of BSP and SHL, promoted inter-molecular interactions (mainly hydrophobic interactions, electrostatic interactions, and hydrogen bonding), modified the instability of BSP, and generated BS complexes with excellent physical, chemical, and functional properties. This study gives us a better understanding of BS complexes and lays the foundation for the loading of active compounds.

Disturbing egg yolk protein structure via pH-shifting treatment for interface reorganization: Improving solubility to enhance oil-water interface adsorption and emulsification properties

This study explored the impact of varying alkalinity levels in pH-shifting treatments on egg yolk protein (EYP) emulsification and investigated the underlying oil-water interface adsorption mechanism. Increasing alkaline pH-shifting treatment exposed more hydrophobic groups within EYP, altering its tertiary structure. Moreover, pH-shifting treatment reduced solution particle size (P < 0.05), possibly by disintegrating insoluble egg yolk granules (EYG) into smaller subunits. Under pH 12.0-shifting conditions, egg yolk (EY) solution reached minimum turbidity and maximum solubility (81.62 %). During initial adsorption, pH 9.0-shifting solution exhibited maximum diffusion rate (0.049 mN/m/s), correlated with minimum solution particle size (88.36 nm). Subsequently, alkaline pH-shifting induced protein rearrangement at the oil-water interface, leading to maximum interfacial pressure (21.01 mN/m) and viscoelastic modulus (44.55 mN/m) under pH 12.0-shifting conditions. This increased emulsion stability by 23.82 % with the lowest creaming index (21.82 %). These findings were crucial for enhancing EYP utilization and promoting EY as a food emulsifier.

Ultrasonic combined pH shifting strategy for improving the stability of emulsion stabilized by yeast proteins: Focused on solubility, protein structure, interface properties

In this study, the improvement mechanism of yeast proteins (YPs) with the ultrasonic and pH shifting treatment on the emulsion stability was investigated through the solubility, protein structure and interface behavior of YPs. Compared with only pH shifting or ultrasound treatment, the solubility of YPs with the combined treatment of ultrasonic and pH shifting was increased significantly. The soluble protein content of pH-U400 reached 85.51 %. The results of YPs structure demonstrated that the β-sheet, α-helix and disulfide bonds contents of YPs with the combined treatment first declined and subsequently increased with increasing ultrasonic power, under alkaline conditions. The fluorescence intensity and surface hydrophobicity first increased and then declined. The more flexible protein structure endowed pH-U400 with lower interfacial tension, higher interfacial diffusion, penetration and reorganization rate, and interfacial protein concentration. The pH-U400 showed the best emulsifying properties (emulsifying activity index was 27.05 m2/g, emulsifying stability index was 31.27 min) and could prepare smaller and more uniform emulsion droplet. The results of multiple light scattering demonstrated that emulsion stabilized by pH-U400 showed the best stability. These results revealed the stability mechanism of emulsions stabilized by YPs and provided guidance for further development of practical YPs products in the food industry.

Carvacrol-loaded emulsions stabilized by soy protein isolate/chitosan oligosaccharide conjugates improved the quality of refrigerated sea bass (Lateolabrax maculatus)

In this study, the soybean protein isolate / chitosan oligosaccharide (SPI/COS) conjugates were developed using glycosylation and used as a stabilizer of carvacrol-loaded emulsions for refrigerating sea bass (Lateolabrax maculatus). The results of Fourier transform infrared spectroscopy and fluorescence spectroscopy showed that COS modified the secondary and tertiary structure of SPI by covalent binding. The SPI/COS conjugate with a mass ratio of SPI and COS of 4:1 (SPI/COS-4) exhibited high glycosylation degree, great water solubility and better emulsification properties. Carvacrol-loaded emulsion stabilized by the SPI/COS-4 (CE-SPI/COS-4) had nanoscale droplet size and remained stable during 40 days of storage. SPI/COS-4 aqueous solution (SPI/COS) and CE-SPI/COS-4 aqueous solution (CE-SPI/COS) in the form of immersion were applied to investigate their preservation effects on sea bass, with sterile water as control check (CK). Sea bass were stored at 4 °C and quality assessments of fish were performed periodically for up to 21 days, which included microbiological and physicochemical analysis. As suggested by microbiological analysis, CE-SPI/COS treatment could significantly inhibit the bacterial growth. The low total volatile basic nitrogen value, thiobarbituric acid value and K-value indicated that CE-SPI/COS greatly retarded protein and lipid oxidation in fish and significantly suppress the degradation of nucleotide. Moreover, fish treated with CE-SPI/COS had minimal color variation and water loss, and maintained hardness, adhesiveness, chewiness, and resilience of fish to the highest degree. Therefore, emulsions stabilized with SPI/COS conjugates may be employed as a potential strategy for the quality maintenance of sea bass.

Complexation between curcumin and walnut protein isolate modified by pH shifting combined with protein-glutaminase

The poor techno-functional properties of walnut protein isolate (WPI) limit its application as carrier to improve bioavailability of curcumin. In this study, WPI was modified by pH-shifting (PS) and protein-glutaminase (PG). Changes on the physicochemical and structural characteristics of WPI and effects on complexation with curcumin were investigated. Treatment of PS plus PG increased electrostatic repulsion of WPI with altered secondary and tertiary structure. Solubility of WPI was greatly improved from 18.09% to 52.90%. The increased flexibility resulted in reduced particle size and increased exposure of hydrophobic groups. The improved amphiphilicity of WPI provided more binding sites for complexation with curcumin. Encapsulation efficiency of curcumin was increased from 32.50% to 94.48%. Interestingly, the formed complexes were able to protect curcumin from degradation with improved storage stability and bioaccessibility. Thus, PS plus PG could serve as effective modification strategy for utilization of WPI as a promising delivery vehicle for hydrophobic bioactives.

Structure-functionality relationship and modification strategies of oat protein: Challenges and opportunities

The increasing preference for plant-based proteins over animal-derived equivalents has intensified research into alternative protein sources, with oats emerging as a noteworthy specialty crop due to their rich array of functional and bioactive components. Despite the growing interest, research into oat proteins remains in its early stages, particularly in understanding the structure-function relationship and modification strategies within food systems. Designing novel food products using oat protein presents both opportunities and challenges; the compact quaternary structure and high thermal stability of oat globulin limit its functionality in diverse applications. This review aims to detail the composition and structural characteristics of oat protein, highlighting the complex relationship between these structural traits and their functional properties. A significant focus is placed on innovative structural modification techniques that enable the cost-effective transformation of oat protein into a functional ingredient or base for new food product development.

Improving the emulsification characteristics of rapeseed protein isolate by ultrasonication assisted pH shift treatment

Rapeseed protein isolate (RPI) is an important nutrimental macronutrient in human diet due to its abundance in amino acids. However the poor emulsifying attributes of RPI limits its application in food industry, which needs to be overcome for its application in food industry. Ultrasonication-aided pH shift (UpHS) treatment is an efficient method for enhancing the functionality of plant/ food protein. In this work, the emulsification characteristics of RPI modified by UpHS technique under different solubility levels were studied. Results showed that the emulsifying activity and stability of modified RPI were significantly improved by 168.46 % (sample with high solubility treated by Ultrasonication-aided pH 12.5, HSpH 12.5) and 134.5 % (sample with high solubility treated by Ultrasonication-aided pH 1.5, HSpH 1.5), respectively compared with the native sample (P < 0.05), and the emulsifying activity was positively correlated (P < 0.05) with solubility. The emulsification stability under acidic condition was higher than that under alkaline condition (HSpH 12.5 increased by 83.5 %). In addition, the adsorption capacity and zeta potential of RPI were increased to 93.74 % and 13.83 % respectively, whereas the particle size and surface tension were reduced to 41.04 % and 23.63 % respectively. This indicates the changes in the molecular structure of modified rapeseed protein, which improved the emulsifying activity of RPI. Moreover, the interfacial film of emulsions formed by the modified protein had stronger compressive resistance, contributing to the enhanced emulsifying stability of the RPI. These results show that UpHS treatment can effectively improve the emulsification properties of proteins, and can be widely used in food industry.

Fabrication and characterization of whey protein isolate-tryptophan nanoparticles by pH-shifting combined with heat treatment

L-Tryptophan (Trp) is an essential amino acid with numerous health benefits. However, incorporating Trp into food products is limited due to its pronounced bitter taste. Encapsulating Trp in nanoparticles by using other natural biopolymers is a potential strategy to mask the bitter taste of Trp in the final products. Whey protein isolate (WPI), composed of alpha-lactalbumin (α-LA), bovine serum albumin (BSA), and beta-lactoglobulin (β-LG), has played a crucial role in delivering bioactive compounds. In order to incorporate Trp within WPI, the present study used a combination of pH-shifting andthermal treatment to fabricatewhey protein isolate-tryptophan nanoparticles (WPI-Trp-NPs). During the pH-shifting technique, WPI unfolds at high pH, such as pH 11, and the dissociated WPI molecules are refolded when pH is shifted back to neutral, creating particles with uniform dispersion and encapsulating smaller particles surrounding them in solution. Further, the well-distributed nanoparticles formed by pH-shifting might encourage the formation of more uniform nanoparticles during subsequent thermal treatment. TheWPI-Trp particles have an average particle size of 110.1 nm and a low average PDI of 0.20. Fluorescence spectroscopy confirmed the encapsulation of Trp by WPI, which shows higher fluorescence when the Trp is encapsulated by the WPI. Surface hydrophobicity, circular dichroism, particle size, free sulfhydryl, and antioxidant activity were used to characterize the WPI-Trp-NPs. WPI-Trp-NPs formed by pH-shifting combined with heating showed a higher surface hydrophobicity and free sulfhydryl content than the untreated WPI-Trp mixture. The conversion of α-helix into random coil in the WPI secondary structure indicated a more disordered structure of the modified whey protein. Molecular docking results indicate the interactions between Trp and WPI, including alpha-lactalbumin (α-LA), bovine serum albumin, and beta-lactoglobulin (β-LG), were mainly driven by hydrophobic interactions and hydrogen bonding. The binding affinity between Trp and these proteins was ranked as α-LA>BSA>β-LG. The combination of pH-shifting and heating improved the functionalityof WPI and was an effective way to fabricate WPI-Trp nanoparticles.

Protein from tiger nut meal extracted by deep eutectic solvent and alkali-soluble acid precipitation: A comparative study on structure, function, and nutrition

Protein from tiger nut meal (TNP) performance high nutritional value. This study optimized the extraction parameters for TNP (DES-TNP) using deep eutectic solvent, with HBD: HBA = 5:1, Liquid: Solid = 11:1, and the moisture content was 15 %. A comprehensive comparison was conducted with the protein extracted using alkali-soluble acid precipitation (ASAE-TNP). DES-TNP demonstrated significantly higher purity (76.21 ± 2.59 %) than ASAE-TNP (67.48 ± 1.11 %). Density functional theory confirmed the successful synthesis of DES and its strong interaction with TNP. Moreover, DES-TNP and ASAE-TNP were different in structure (microscopic, secondary, and tertiary) and molecular weight distribution. The discrepancy contributed to the different functional properties, DES-TNP exhibiting better solubility, emulsification and foaming properties at pH13 compared to ASAE-TNP. For nutritional properties, DES-TNP and ASAE-TNP exhibited similar amino acid composition and digestibility, but the total amino acid content of DES-TNP was higher. This study presented a novel method for the extraction and comprehensive utilization of TNP.

Exploring community succession and metabolic changes in corn gluten meal-bran mixed wastes during fermentation

Addressing the challenge of sustainable agricultural processing waste management is crucial. Protein sources are essential for livestock farming, and one viable solution is the microbial fermentation of agricultural by-products. In this study, the microorganisms utilized for fermentation were Pichia fermentans PFZS and Limmosilactobacillus fermentum LFZS. The results demonstrated that the fermented corn gluten meal-bran mixture (FCBM) effectively degraded high molecular weight proteins, resulting in increases of approximately 23.3%, 367.6%, and 159.3% in crude protein (CP), trichloroacetic acid-soluble protein (TCA-SP), and free amino acid (FAA), respectively. Additionally, there was a significant enhancement in the content of beneficial metabolites, including total phenols, carotenoids, and microorganisms. FCBM also effectively reduced anti-nutritional factors while boosting antioxidant and anti-inflammatory substances, such as dipeptides and tripeptides. The fermentation process was marked by an increase in beneficial endophytes, which was closely correlated with the enhancement of beneficial metabolites. Overall, FCBM provides a theoretical basis for substituting traditional protein resources in animal husbandry.

Rice proteins - Gum arabic coacervates: Effect of pH and polysaccharide concentration in oil-in-water emulsion stability

In the context of replacing animal proteins in food matrices, rice proteins (RP) become promised because they come from an abundant plant source, are hypoallergenic, and have high digestibility and nutritional value. However, commercial protein isolates obtained by spray drying have low solubility and poor functionality, especially in their isoelectric point. One way to modify these properties is through interaction with polysaccharides, such as gum arabic (GA). Therefore, this work aims to evaluate the effects of pH and GA concentration on the interaction and emulsifying activity of RP:GA coacervates. First, the effects of pH (2.5 to 7.0) and GA concentrations (0.2 to 1.0 wt%, giving rise to RP:GA mass ratios of 1:0.2 to 1:1.0) in RP:GA blends were evaluated. The results demonstrated that biopolymers present opposite net charges at pH between 2.5 and 4.0. At pH 3.0, insoluble coacervates with complete charge neutralization were formed by electrostatic interactions, while at pH 5.0 it was observed that the presence of GA prevented the RP massive aggregation. Second, selected blends with 0.4 or 1.0 wt% of GA (RP:GA mass ratios of 1:0.4 or 1:1.0) at pH 3.0 or 5.0 were tested for their ability to stabilize oil-in-water emulsions. The emulsions were characterized for 21 days. It was observed that the GA increased the stability of RP emulsions, regardless of the pH and polysaccharide concentration. Taken together, our results show that it is possible to combine RP and GA to improve the emulsifying properties of these plant proteins at pH conditions close to their isoelectric point, expanding the possibility of implementation in food systems.

Modifications of whey proteins for emulsion based applications: Current status, issues and prospectives

Whey proteins are a major group of dairy proteins with high potential for various food based applications. Whey protein isolate has a limited range of functionalities. This functional range can be expanded using diverse modification methods to suit specific applications. This review summarizes the recent advances in the modifications of whey proteins using chemical, physical, and enzymatic methods and their combinations as well as the modification effects on the physicochemical properties. The uses of these modified whey proteins in emulsion based food and beverage systems are described. The limitations in the studies summarized are critically discussed, while future research directions are suggested on how to better utilize whey proteins for emulsion based uses through modifications.

Characteristics of Quinoa Protein Isolate Treated by Pulsed Electric Field

The aim of this study was to investigate the impact of a pulsed electric field (PEF) on the structural and functional properties of quinoa protein isolate (QPI). The findings revealed a significant alteration in the secondary structure of QPI following PEF treatment, converting the random coil into the β-sheet, resulting in an improvement in structure orderliness and an enhancement of thermal stability. The PEF treatment led to a reduction in particle size, induced structural unfolding, and increased the surface hydrophobicity, resulting in a statistically significant enhancement in the solubility, foaming, and emulsifying properties of QPI (p < 0.05). Specifically, PEF treatment at 7.5 kV/cm for 30 pulses was identified as the optimal condition for modifying QPI. This study provides a basis for the precision and range of application of pulsed electric field treatment and offers the possibility of improving the physical and chemical properties of quinoa protein.

Effect of Molecular Weight on the Structural and Emulsifying Characteristics of Bovine Bone Protein Hydrolysate

The emulsifying capacity of bovine bone protein extracted using high-pressure hot water (HBBP) has been determined to be good. Nevertheless, given that HBBP is a blend of peptides with a broad range of molecular weights, the distinction in emulsifying capacity between polypeptide components with high and low molecular weights is unclear. Therefore, in this study, HBBP was separated into three molecular weight components of 10-30 kDa (HBBP 1), 5-10 kDa (HBBP 2), and <5 kDa (HBBP 3) via ultrafiltration, and the differences in their structures and emulsifying properties were investigated. The polypeptide with the highest molecular weight displayed the lowest endogenous fluorescence intensity, the least solubility in an aqueous solution, and the highest surface hydrophobicity index. Analysis using laser confocal Raman spectroscopy showed that with an increase in polypeptide molecular weight, the α-helix and β-sheet contents in the secondary structure of the polypeptide molecule increased significantly. Particle size, rheological characteristics, and laser confocal microscopy were used to characterize the emulsion made from peptides of various molecular weights. High-molecular-weight peptides were able to provide a more robust spatial repulsion and thicker interfacial coating in the emulsion, which would make the emulsion more stable. The above results showed that the high-molecular-weight polypeptide in HBBP effectively improved the emulsion stability when forming an emulsion. This study increased the rate at which bovine bone was utilized and provided a theoretical foundation for the use of bovine bone protein as an emulsifier in the food sector.