Modification of structure and functionalities of ginkgo seed proteins by pH-shifting treatment

Thiol-modified hyaluronic acid and hydroxyl radical-induced oxidation synergistically enhance the gelling capacity of ginkgo seed proteins

The objective of this work was to investigate the effect of synthetic thiol-modified hyaluronic acid (HASH) on the gelation properties of ginkgo seed protein isolate (GSPI) under non-oxidizing (NOX) or oxidizing (OX) conditions. Under NOX conditions, HASH mediated the disruption of disulfide bonds, leading to a dose-dependent dissociation of GSPI. Conversely, in OX conditions, hydroxyl radical-induced oxidation facilitated the formation of interprotein disulfide bonds. Incremental increases in HASH concentration were found to significantly enhance the textural characteristics of the GSPI gel, achieving optimal elasticity. Moreover, HASH incorporation conferred increased rigidity and porosity to the gel matrix, markedly improving the water holding capacity and reducing the protein leachability. Additionally, OX conditions amplified the beneficial effect of HASH on gel strength and hydration properties. This study elucidates a novel approach for enhancing the gel properties of GSPI and modulating protein-polysaccharide interaction through the chemical modification of natural polysaccharides.

Effect of transglutaminase treatment on the physicochemical properties and structural characteristics of soy protein isolate/konjac glucomannan complex

In this study, the effects of transglutaminase on the structural and physicochemical properties of soy protein isolate/konjac glucomannan complex were investigated. Additionally, the complex was treated with different transglutaminase additions, cross-linking temperatures, and cross-linking pH and compared with a control without transglutaminase to elucidate the effect of transglutaminase on the internal interactions within the complex. The results demonstrated that transglutaminase treatment significantly enhanced the water-holding and oil-binding capacities by 34.62 % and 49.28 %, respectively, along with the emulsifying properties. Furthermore, transglutaminase treatment significantly enhanced the UV absorption intensity by 36.89 % and strengthened the intermolecular interactions. The relative crystallinity and ΔH were elevated by 15.08 % and 34.39 %, respectively, which significantly enhanced the thermal stability of the complex. Overall, the transglutaminase-treated complex displayed improved physicochemical properties, with a more organized, uniform, and denser internal structure. These findings offer valuable insights into developing novel plant-based fat mimetics.

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.

Effects of plasma-activated water on structural and functional properties of PSE-like chicken protein isolate

Pale, soft and exudative (PSE)-like chicken meat is rich in high-quality proteins, however, due to the properties of PSE-like meat, the functional characteristics of PSE-like chicken meat protein isolate (PPI) are affected. The present investigation aimed to improve the functional properties of PPI by employing plasma activation water (PAW), with the ultimate goal of enhancing its utility in various applications. The effects of PAW on the structure and function of PPI were evaluated. PAW treatment induced the protein structure to change from random coil to α-helix, which made the protein conformation more stable. PAW caused the hydrophobic residues to be exposed, thereby effectively enhancing their surface hydrophobicity. Dynamic rheology revealed the storage modulus of PPI gradually raised with increasing of PAW activation time. The scanning electron microscopy (SEM) showed that PAW promoted PPI to form a rough surface. When PAW activation time increased to 40 s, the foaming ability of PPI was raised by 77.84%, the emulsifying activity index was increased to 20.94 m2/g, the emulsion stability index was improved by 20.40%, and the in vitro digestibility was increased by 25.15% (P < 0.05). The above results showed PAW could modify the structural properties, and effectively improve the emulsifying and foaming properties of PPI, and increase the in vitro digestibility of PPI.

Effect of magnetic induction electric field treatment of soybean protein isolate on their structural and interfacial properties

Induction electric field (IEF) technology is a new green treatment technology based on electric field, and its application has not been widely reported, especially in the direction of soybean protein isolate (SPI) modification. Therefore, IEF and several commonly used physical modification methods were used to investigate the effect on the structure and interfacial properties of SPI. The IEF treatment was found to be superior to the other groups in terms of emulsification performance, solubility and flexibility, which were enhanced by 44.61 %, 16.33 % and 30.55 %, as compared to untreated SPI. DSC shows more prominent thermal stabilisation of proteins after treatment. Secondary structure measurements revealed a decrease in α-helix content and an increase in random coil content, as well as an increase in surface hydrophobicity and free sulfhydryl groups, demonstrating a shift towards a loosely packed and disordered protein structure. At the same time, the IEF treatment particle size reaches a minimum and is uniformly distributed under the microscope, showing specific advantages in stabilising emulsions. In short, IEF provides a new way of thinking about protein modification, which is conducive to expanding the range of applications in the food industry.

Binding mechanism and structural characteristics of alloyed protein complex for enhanced solubility of hemp seed protein isolate

Despite the numerous health benefits and high digestibility of hemp seed protein isolate (HPI), its low solubility at neutral pH limits its utilization in the food industry. Therefore, we subjected insoluble HPI and soluble mung bean protein isolate (MBPI) to pH co-shifting under extremely alkaline conditions to form an alloyed protein complex (A-HM). At a mass ratio of HPI:MBPI of 50:50, A-HM exhibited the highest solubility (95.30 ± 0.99 %), and also had high resistance to heat treatment. Native PAGE demonstrated the formation of alloyed protein complexes, and particle size analysis revealed that A-HM exhibited small particle sizes and dispersion in water without aggregation of HPI. Owing to their small size, numerous hydrophobic residues and aromatic ring of HPI were exposed on the surface. Hydrophobic interactions predominantly governed the binding force involved in the formation of A-HM. Our findings may enhance HPI applications in the food industry, particularly in plant-based beverages.

Soluble nano-sized aggregates of Alaska pollock proteins engineered by the refolding process of pH-shifting

Alaska pollock proteins (PPs) are aquatic proteins with a compact structure, which leads to poor solubility and limited application in food industries. This study explored the structural assembly and gelation behavior of the PP-soluble aggregates prepared by the refolding processing of acidic (pH 1.5-7) or alkaline (pH 12-7) pH-shifting treatment. PPs refolded at alkali pHs produced more soluble aggregates than at acid pHs. Lots of myosin heavy lights (MHCs) could interact with actin to form soluble aggregates at high pH rather than low pH. When shifting back to pH 7, the solubility of alkaline-shifted PPs was boosted to over 60% with a more flexible structure, while acidic-shifted PPs showed reduced solubility (29%) with increased rigidity. Molecular characteristics results indicated that alkaline-shifted PPs comprising MHCs and actin exhibited higher surface hydrophobicity and sulfhydryl groups. These structural modifications induced by alkaline pH-shifting contributed to improving the gelling, emulsifying and foaming properties of PPs. Intriguingly, both acidic- and alkaline-shifted PPs showed a retarded digestive behavior. These novel insights may be adaptable to other animal proteins for modulating the protein structure-functionality, expanding their applications in food industries.

Hyaluronic acid promotes heat-induced gelation of ginkgo seed proteins

This study aimed to investigate how varying concentrations (0.01-0.5 %, w/v) and molecular weights (50, 500, 1500 kDa) of hyaluronic acid (HA) affect the physicochemical properties of heat-induced ginkgo seed protein isolate (GSPI)-HA composite gel. Incorporating HA increased viscosity (up to 14 times) and charge (up to 23 %) of GSPI-HA aggregates, while reducing particle size (up to 31 %) and improving gel texture, particularly with high molecular weight HA. However, high concentrations (0.5 %, w/v) of HA weakened gel texture. Non-covalent bonds primarily drive the formation of a continuous gel network between HA and GSPI, resulting in small pores and enhanced hydration properties. With increasing HA molecular weight, non-covalent interactions between GSPI and HA increased, leading to improved gel thermal stability. Overall, the study suggests that manipulating the molecular weight and concentration of HA can enhance the gelling properties of GSPI, leading to the development of a diverse array of GSPI-HA composite gels with varied properties.

Modification of soybean lipophilic protein based on pH-shifting and high-pressure homogenization: Focus on structure, physicochemical properties and delivery vehicle

High-pressure homogenization and pH-shifting can be used to modify soybean lipophilic protein (SLP), and to enhance its ability to deliver vitamin B12. The structural changes of SLP were analyzed by multispectral techniques and the results showed that secondary and tertiary structures of SLP were altered by modification. The modification unfolded the SLP structure, released more free hydrogen ions, and increased positive charge density on the protein surface. Also, the solubility of modified SLP increased by maximum of 34.75 %. Furthermore, molecular docking showed that complexes were formed between SLP and vitamin B12 mainly through hydrogen bonding and hydrophobic interactions, and the encapsulation rate of modified SLP was maximally increased by 2.3 %. In vitro digestion showed that modified SLP enhanced stability and bioaccessibility of vitamin B12. This study provides theoretical basis for modification of SLP and effective delivery of bioactive substances.

Response surface optimization of protein extraction from cold-pressed terebinth (Pistacia terebinthus L.) oil byproducts: Physicochemical and functional characteristics

The current study focused on optimizing the extraction parameters of terebinth seed proteins from cold-pressed terebinth oil byproducts to maximize protein purity and protein yield. The isolated proteins were characterized to evaluate their properties; thus revealing the valorization potential of these byproducts. Response surface methodology was used to detect the effect of three extraction parameters (pH, temperature, and time). The protein isolates were studied for their physicochemical and functional characteristics. The results indicated that an extraction pH of 8, a temperature of 50°C, and an extraction period of 60 min are optimum conditions for obtaining protein isolates with the highest purity. On the other hand, it was demonstrated that an extraction pH of 12, a temperature of 46.4°C, and an extraction duration of 102.4 min were optimum conditions for the maximum protein yield. The proteins produced under these two sets of conditions, referred to as TRP (terebinth protein with maximum purity) and TRY (terebinth protein with maximum yield), respectively, exhibited comparable oil absorption capacity (OAC), foaming, emulsifying capabilities, and stability. Both proteins showed the highest solubility at pH 11, and their zeta potentials approached zero at pH 4, indicating proximity to their isoelectric points. However, FRAP and DPPH assays showed that TRP and TRY offered low antioxidative capacity. The high β-sheet content in TRP and TRY suggests enhanced thermal stability but reduced digestibility of these proteins. Therefore, in addition to protein enrichment, TRP and TRY protein isolates can be utilized in muffins and other food applications thanks to their favorable oil absorption, foaming and emulsifying capacities, and thermal stabilities.

Effect of ultrasound-assisted pH-shifting treatment on the physicochemical properties of melon seed protein

Melon seeds have received considerable attention in recent years because of their high protein content, but they have not yet been fully used. The modification of melon seed protein (MSP) using ultrasound-assisted pH-shifting treatment was investigated in this study by analyzing structural characteristics and functional properties. The particle size, free sulfhydryl content, surface hydrophobicity, solubility, secondary structure, water-holding capacity, oil-holding capacity, emulsification activity index, and emulsification stability index of MSP were determined. MSP treated with ultrasound-assisted, pH-shifting had a smaller particle size, lower free sulfhydryl content, higher surface hydrophobicity, and solubility increased from 43.67 % to 89.12 %. The secondary structure of MSP was affected by ultrasonic treatment, manifesting as an α-helix increase and β-helix, β-turn, and random coil content decrease, which may be the reason why the protein structure became more compact after treatment. The water and oil holding capacities of MSP increased from 2.74 g/g and 3.14 g/g in untreated samples to 3.19 g/g and 3.97 g/g for ultrasound-treated samples, and further increased to 3.97 g/g and 5.02 g/g for ultrasound-assisted, pH-shifting treatment at pH 9.0, respectively. The emulsification activity index of MSP was 21.11 m2/g before treatment and reached a maximum of 32.34 m2/g after ultrasound-assisted, pH-shifting treatment at pH 9.0. The emulsification stability of MSP was maximized by ultrasonic treatment at pH 7.0. Ultrasound-assisted, pH-shifting treatment can effectively improve the functional properties of MSP by modifying the protein structure, which improves the potential application of melon seed protein in the food industry.

pH-shifting treatment improved the emulsifying ability of gelatin under low-energy emulsification

The effects of pH-shifting treatments (pH 3, 5, 7, 9, and 11) on the stability of gelatin emulsions made by low-energy stirring were investigated. pH-shifting treatments significantly enhanced the ESI and EAI of the emulsion (P < 0.05) and reduced its particle size (P < 0.05) under low-energy emulsifying conditions. The pH11-7 shifting treatment significantly increased the degree of depolymerization and the level of ordered structure of gelatin (P < 0.05). These transformations resulted in a significant increase in the exposure of hydrophobic and negatively charged residues (P < 0.05) on the surface of gelatin, facilitating a faster adsorption rate of gelatin onto the oil-water interface as well as an increase in the amount of gelatin adsorbed at the interface. Moreover, the alkali-shifting treatment promoted the formation of a thin viscoelastic interfacial film, which contributed to the enhanced stability of the emulsion.

Hydroxyl radical-induced oxidation boosts the gelation of ginkgo seed protein in the presence of hyaluronic acid

Hydroxyl radical-induced oxidation can modify gelling properties of food proteins. In this study, a hydroxyl radical generating system (HRGS), consisting of 0.1 mM Fe3+, 0.1 mM ascorbic acid, and 1, 10, or 20 mM H2O2, was used to oxidize ginkgo seed protein isolate (GSPI) for 4 h at ambient temperature in the presence of 0.3 % (w/v) hyaluronic acid (HA) to enhance its gelation properties. HRGS treatment led to increased protein hydrophobicity, reduced sulfhydryl content, and disulfide bond-mediated protein crosslinking. Moreover, the secondary structure of GSPI varied with H2O2 concentrations. Moderate oxidation (approximately 10 mM H2O2) promoted GSPI aggregation and improved mechanical strength, rheological properties, water holding capacity, and whiteness of GSPI gels. However, excessive oxidation disrupted hydrogen bonding, generated excessive disulfide bonds, hindered active group interaction, inhibited gel network formation, and reduced gel strength. Hence, hydroxyl radical-induced oxidation holds potential for enhancing GSPI gelation within specific concentration ranges. This study suggests that controlled oxidation could be a novel approach for developing protein-based gel products.

Improvement of processable properties of plant-based high internal phase emulsions by mung bean protein isolate based on pH shift treatment

BACKGROUND

High internal phase emulsions (HIPEs) are unique emulsion systems that transform liquid oil into solid-like fats, thus avoiding the use of saturated fat and leading to a healthier and more sustainable food system for consumers. HIPEs with oil volume fraction (ϕ) of 75-85% were fabricated with mung bean protein isolate (MPI) under different pH shift treatments at 1.0% concentration through the one-step method. In the present study, we investigated the physical properties, microstructures, processing properties, storage stability and rheological properties of HIPEs.

RESULTS

The results suggested that the properties of MPI under different pH shift treatments were improved to different degrees, stabilizing HIPEs (ϕ = 75-85%) with various processability to meet food processing needs. Under alkali shift treatment conditions, the particle size of MPI was significantly reduced with better solubility. Moreover, the exposure of hydrophobic groups increased the surface hydrophobicity of MPI, awarding MPI better emulsifying properties, which could stabilize the HIPEs with higher oil phase fraction. In addition, the MPI under pH 12 shift treatment (MPI-12) had the best oil-carrying ability to form the stable HIPEs with oil volume fraction (ϕ) up to 85%, which was the highest oil phase in preparing the HIPEs using plant protein solely at a low concentration under neutral conditions.

CONCLUSION

A series of stable HIPEs with different processing properties was simply and feasibly fabricated and these are of great potential in applying edible HIPEs. © 2024 Society of Chemical Industry.

A comprehensive review on the recent trends in extractions, pretreatments and modifications of plant-based proteins

Plant-based proteins offer sustainable and nutritious alternatives to animal proteins with their techno-functional attributes influencing product quality and designer food development. Due to the inherent complexities of plant proteins, proper extraction and modifications are vital for their effective utilization. This review highlights the emerging sources of plant-based proteins, and the recent statistics of the techniques employed for pretreatment, extraction, and modifications. The pretreatment, extraction and modification approach to modify plant proteins have been classified, addressed, and the recent applications of such methodologies are duly indicated. Furthermore, this study furnishes novel perspectives regarding the potential impacts of emerging technologies on the intricate dynamics of plant proteins. A thorough review of 100 articles (2018-2024) shows the researchers' keen interest in investigating novel plant proteins and how they can be used; seeds being the main source for protein extraction, followed by legumes. Use of by-products as a protein source is increasing rapidly, which is noteworthy. Protein studies still lack knowledge on protein fraction, antinutrients, and pretreatments. The use of physical methods and their combination with other techniques are increasing for effective and environmentally friendly extraction and modification of plant proteins. Several studies explore the effect of protein changes on their function and nutrition, especially with a goal of replacing ingredients with plant proteins that have improved or enhanced qualities. However, the next step is to investigate the sophisticated modification methods for deeper insights into food safety and toxicity.

Docosahexaenoic acid-mediated milk protein treated by ultrasound-assisted pH shifting for enhanced astaxanthin delivery and processed cheese application

Whey protein isolate (WPI)-based nanodelivery systems have recently attracted an increasing amount of attention. Despite this, research focusing on milk protein concentrate (MPC) and micellar casein (MCC) as carriers loaded in hydrophobic compounds is lacking. This study investigated the mediated effect of docosahexaenoic acid (DHA) in 3 different milk proteins for the embedding of astaxanthin (ASTA) after ultrasound-assisted pH-shifting treatment. We then evaluated the application of milk protein carriers in cheese processing by comparing MPC, MCC, and WPI. The particle size, polydispersity index, and zeta potential results of the milk protein-DHA complex suggested that the addition of 0.36 μmol/mL DHA optimized the delivery of milk protein to ASTA. All 3 DHA-mediated milk proteins induced an improvement in encapsulation efficiency and antioxidant properties of ASTA. Furthermore, the DHA-mediated MPC and MCC played a stronger role in improving the bioaccessibility and thermal and storage stability of ASTA than those without DHA. Tests conducted to examine the application in cheese production indicated that MCC carrier had a positive effect on the texture of cheeses. However, the delivery effect was dependent on the milk protein variety, and MCC exhibited the best protection ability of ASTA, followed by MPC and WPI. The simulated digestion and storage stability results of cheese further confirmed that the protein encapsulation mediated by DHA was more conducive to ASTA absorption. These findings suggested that the DHA-mediated milk protein complexes studied here may be suitable hydrophilic delivery carriers for the hydrophobic nutrient ASTA, potentially playing different roles in improving its storage stability and bioaccessibility.

Changes in physicochemical, structural and functional properties, and lysinoalanine formation during the unfolding and refolding of pH-shifted black soldier fly larvae albumin

The changes of physicochemical, structural and functional properties and the lysinoalanine (LAL) formation during the unfolding and refolding of black soldier fly larvae albumin (BSFLA) induced by acid/alkaline pH shift were explored. The results showed that acid/alkaline conditions induced unfolding of BSFLA structure, but also accompanied by the formation of some large aggregates due to the hydrophobic interactions, hydrogen bonds, and disulfide bonds. Compared with control or pH1.5 shift, pH12 shift treatment significantly increased the electrostatic repulsion, surface hydrophobicity, free sulfhydryl group, and deamidation reactions, but reduced the fluorescence intensity of BSFLA, and these change in protein conformation contributed to increase in solubility, emulsion activity, and emulsion stability. But the content of LAL in BSFLA was increased by 93.39 % by pH 12 shift treatment. In addition, pH1.5 shift modified BSFLA tended to form β-sheet structure through unfolding and refolding, resulting in the formation of aggregates with larger particle sizes, and reducing the solubility and the LAL content by 7.93 % and 65.53 %, respectively. SDS-PAGE profile showed that pH12/1.5 shifting did not cause irreversible denaturation of protein molecules. Therefore, pH12-shift is good way to improve the functional properties of BSFLA, but the content of LAL should be reduced to make it better used in food.

Unraveling the effect of combined heat and high-pressure homogenization treatment on the improvement of chickpea protein solubility from the perspectives of colloidal state change and structural characteristic modification

Chickpea protein (CP) is a promising plant protein ingredient, but the poor solubility has limited its broad application. In this study, heating followed by high-pressure homogenization (HPH) was used to improve the solubility of CP. The results showed that combined heat (80℃, 30 min) and HPH (80 MPa, 2 cycles) treatment exhibited an additive effect in improving the solubility of CP. This improvement could be attributed to the dissociation and the rearrangement of large insoluble protein aggregates into small-sized soluble protein aggregates, the increased exposure of hydrophobic residues and reactive sulfhydryl groups, the transformation of α-helices to β-sheets and β-turns. Moreover, the 11S subunits of CP could form reinforced disulfide covalent cross-links under heating + HPH, which may provide steric hindrance preventing the reassembly of large protein bodies. This work proposes an interesting approach to enhance the physicochemical properties of CP for tailoring techno-functional plant protein ingredients in food formulations.

Dynamic changes in the aggregation-depolymerization behavior of Ovomucin-Complex and its binding to urease during in vitro simulated gastric digestion

Ovomucin-Complex extracted from egg white is expected to have a barrier function similar to gastric mucin. In this study, the dynamic changes in structure, rheological properties and binding ability of Ovomucin-Complex during in vitro simulated gastric digestion were investigated. The results from HPLC and CLSM showed that extremely acidic pH (pH = 2.0) promoted Ovomucin-Complex to form aggregation. Acid-induced aggregation may hinder its binding to pepsin, thus rendering Ovomucin-Complex resistant to pepsin. Consequently, most of the polymer structure and weak gel properties of Ovomucin-Complex retained after simulated gastric digestion as verified by HPLC, CLSM and rheological measurement, although there was a small breakdown of the glycosidic bond as confirmed by the increased content of reducing sugar. The significantly reduced hydrophobic interactions of Ovomucin-Complex were observed under extremely acidic conditions and simulated gastric digestion compared with the native. Noticeably, the undigested Ovomucin-Complex after simulated gastric digestion showed a higher affinity (KD = 5.0 ± 3.2 nm) for urease - the key surface antigen of Helicobacter pylori. The interaction mechanism between Ovomucin-Complex and urease during gastric digestion deserves further studies. This finding provides a new insight to develop an artificial physical mucus barrier to reduce Helicobacter pylori infection.

Optimization of extraction parameters of protein isolate from milk thistle seed: Physicochemical and functional characteristics

In the current study, optimization of milk thistle protein extraction parameters was carried out in terms of purity and yield. In addition, the characterization of proteins isolated from milk thistle seeds was conducted. The optimal conditions for achieving the highest purity of protein (MTP) from milk thistle seeds were identified as extraction pH 9.47, temperature 30°C, and extraction time 180 min. Conversely, optimal values for overall protein yield (MTY) were determined at extraction pH 12, temperature 50°C, and extraction time 167 min. The proteins obtained under these two sets of conditions (MTP and MTY) demonstrated comparable oil absorption capacity (OAC), foaming, and emulsifying capabilities, as well as stability, aligning with findings from previous studies on seed protein. Both proteins had the highest protein solubilities at pH 11. Both proteins' zeta potentials were closest to zero at pH 4, demonstrating their closeness to the isoelectric point. MTP and MTY had poorer antioxidant capabilities than the other protein isolates/concentrates. MTP and MTY contain high β sheet concentrations that might enhance thermal stability and lower the digestibility of proteins. In conclusion, the protein extraction process demonstrated a high potential for achieving both substantial yield and remarkable purity with some decent technological and functional properties, thus holding promise for various applications in diverse fields.

Research progress on plant-based protein Pickering particles: Stabilization mechanisms, preparation methods, and application prospects in the food industry

At present, there have been many research articles reporting that plant-based protein Pickering particles from different sources are used to stabilize Pickering emulsions, but the reports of corresponding review articles are still far from sufficient. This study focuses on the research hotspots and related progress on plant-based protein Pickering particles in the past five years. First, the article describes the mechanism by which Pickering emulsions are stabilized by different types of plant-based protein Pickering particles. Then, the extraction, preparation, and modification methods of various plant-based protein Pickering particles are highlighted to provide a reference for the development of greener and more efficient plant-based protein Pickering particles. The article also introduces some of the most promising applications of Pickering emulsions stabilized by plant-based protein Pickering particles in the food field. Finally, the paper also discusses the potential applications and challenges of plant-based protein Pickering particles in the food industry.

L-Theanine Improves the Gelation of Ginkgo Seed Proteins at Different pH Levels

L-theanine (L-Th), a non-protein amino acid naturally found in teas and certain plant leaves, has garnered considerable attention due to its health benefits and potential to modify proteins such as ginkgo seed proteins, which have poor gelling properties, thereby expanding their applications in the food industry. The objective of this study was to investigate the impact of varying concentrations of L-Th (0.0%, 0.5%, 1.0%, and 2.0%) on the gelling properties of ginkgo seed protein isolate (GSPI) at various pH levels (5.0, 6.0, and 7.0). The GSPI gels exhibited the highest strength at a pH of 5.0 (132.1 ± 5.6 g), followed by a pH of 6.0 (95.9 ± 3.9 g), while a weak gel was formed at a pH of 7.0 (29.5 ± 0.2 g). The incorporation of L-Th increased the hardness (58.5-231.6%) and springiness (3.0-9.5%) of the GSPI gels at a pH of 7.0 in a concentration-dependent manner. However, L-Th did not enhance the gel strength or water holding capacity at a pH of 5.0. The rheological characteristics of the GSPI sols were found to be closely related to the textural properties of L-Th-incorporated gels. To understand the underlying mechanism of L-Th's effects, the physicochemical properties of the sols were analyzed. Specifically, L-Th promoted GSPI solubilization (up to 7.3%), reduced their hydrophobicity (up to 16.2%), reduced the particle size (up to 40.9%), and increased the ζ potential (up to 21%) of the sols. Overall, our findings suggest that L-Th holds promise as a functional ingredient for improving gel products.

Effects of Germination on the Structure, Functional Properties, and In Vitro Digestibility of a Black Bean (Glycine max (L.) Merr.) Protein Isolate

The utilization of black beans as a protein-rich ingredient presents remarkable prospects in the protein food industry. The objective of this study was to assess the impact of germination treatment on the physicochemical, structural, and functional characteristics of a black bean protein isolate. The findings indicate that germination resulted in an increase in both the total and soluble protein contents of black beans, while SDS-PAGE demonstrated an increase in the proportion of 11S and 7S globulin subunits. After germination, the particle size of the black bean protein isolate decreased in the solution, while the absolute value of the zeta potential increased. The above results show that the stability of the solution was improved. The contents of β-sheet and β-turn gradually decreased, while the content of α-helix increased, and the fluorescence spectrum of the black bean protein isolate showed a red shift phenomenon, indicating that the structure of the protein isolate and its polypeptide chain were prolonged, and the foaming property, emulsification property and in vitro digestibility were significantly improved after germination. Therefore, germination not only improves functional properties, but also nutritional content.

Effect of pH-shifting on the water holding capacity and gelation properties of mung bean protein isolate

In this study, alkaline pH-shifting modified the globular structure of mung bean protein isolate (MBPI) to form flexible and stretched structures. In contrast, acidic pH-shifting increased the rigidity of MBPI. The increased flexibility (at the level of the secondary structure) and newly exposed intermolecular amino acid groups induced by alkaline pH-shifting improved the water holding capacity and gelation properties of proteins. Specifically, MBPI treated at pH 12 (MP12) showed the most flexible structure and highest water holding capacity and gel formation properties (least gelation concentration). The water-holding capacity of native MBPI increased from 1.56 g/g to 4.81 g/g, and its least gelation concentration decreased from 22 % to 15 % by pH-shifting at pH 12. Furthermore, MP12 formed stronger and more elastic heat-induced gels than native MBPI. We identified significant differences in the structural properties and water holding capacity, and gelation properties of acidic and alkaline pH-shifted MBPI and investigated the gelation properties of MP12 including rheological and morphological analyses. Our findings can facilitate the use of mung beans as a protein source in a wide range of food applications, including plant-based and processed meats.

Comparison of milk protein concentrate, micellar casein, and whey protein isolate in loading astaxanthin after the treatment of ultrasound-assisted pH shifting

Milk proteins can be used as encapsulation walls to increase the bioavailability of active compounds because they can bind hydrophobic, hydrophilic, and charged compounds. The objective of this study was to investigate the effects of astaxanthin (ASTA) encapsulation and the functional properties of milk protein and ASTA nanocomposites by an ultrasound-assisted pH-shifting treatment of different milk proteins, including milk protein concentrate (MPC), micellar casein (MCC), and whey protein isolate (WPI). The ultrasound-assisted pH-shifting treatment of milk protein helped to improve the encapsulation rate of ASTA. Therein, MCC showed great improvement of encapsulating ASTA after co-treatment with the raised encapsulated rate of 5.11%, followed by WPI and MPC. Furthermore, the nanocomposites of ASTA with milk protein exhibit improved bioavailability, antioxidant capacity, and storage stability. By comparison, MCC-encapsulated ASTA has the best storage stability, followed by MPC, and WPI-encapsulated ASTA has the least stability over a 28-d storage period. The results of intrinsic fluorescence and surface hydrophobicity showed that milk protein underwent fluorescence quenching after binding to ASTA, which was due to the hydrophobic sites of the protein being occupied by ASTA. In general, the nanocomposites of milk protein and ASTA fabricated by using an ultrasound-assisted pH-shifting treatment have the potential to be better nano-delivery systems for ASTA in functional foods, especially MCC, which showed excellent performance in encapsulation after treatment technique.

Redesign of air/oil-water interface via physical fields coupled with pH shifting to improve the emulsification, foaming, and digestion properties of plant proteins

The application of plant proteins in food systems is largely hindered by their poor foaming or emulsifying properties and low digestibility compared with animal proteins, especially due to the aggregate state with tightly folded structure, slowly adsorbing at the interfaces, generating films with lower mechanical properties, and exposing less cutting sites. Physical fields and pH shifting have certain synergistic effects to efficiently tune the structure and redesign the interfacial layer of plant proteins, further enhancing their foaming or emulsifying properties. The improvement mechanisms mainly include: i) Aggregated plant proteins are depolymerized to form small protein particles and flexible structure is more easily exposed by combination treatment; ii) Particles with appropriate surface properties are quickly adsorbed to the interfacial layer, and then unfolded and rearranged to generate a tightly packed stiff interfacial layer to enhance bubble and emulsion stability; and iii) The unfolding and rearrangement of protein structure at the interface may result in the exposure of more cutting sites of digestive enzymes. This review summarizes the latest research progress on the structural changes, interfacial behaviors, and digestion properties of plant proteins under combined treatment, and elucidates the future development of these modification technologies for plant proteins in the food industry.

Isolation, virtual screening, action mechanisms, chelation with zinc ions, and stability of ACE-inhibitory peptides from ginkgo seed globulin

Ginkgo seed has potential applications in the prevention and treatment of hypertension, but its application in food is limited. Thus, ginkgo seed globulin was hydrolyzed using dual enzymes (Alcalase and thermolysin). After gel column separation, reverse-phase high-performance liquid chromatographic purification, and ESI-MS/MS analysis, five oligopeptides containing fewer than 12 amino acid residues were obtained. Among them, the heptapeptide Glu-Ala-Ser-Pro-Lys-Pro-Val (EASPKPV) offered relatively high capacities to inhibit ACE (IC50: 87.66 μmol L-1) and bind with zinc ions (5.35 ± 0.32 mg g-1). Moreover, EASPKPV showed competitive inhibitory kinetics against ACE. Fourier-transform infrared spectroscopy analysis evidenced that the amino group and carboxyl group of EASPKPV could both provide binding sites for zinc ions. EASPKPV can restrain ACE in the following ways: (i) competitively linking with five key residues (Gln281, Ala354, Glu376, Lys511, and Tyr523) in the S1 and S2 pockets of ACE by short hydrogen bonds; (ii) binding to thirteen active residues of ACE via hydrophobic interactions; and (iii) binding with residue His383 or the zinc ion of zinc tetrahedral coordination. Additionally, simulated gastrointestinal digestion did not show any remarkable efficacy on the capacities of EASPKPV to restrain ACE and bind with zinc ions. These results indicate that ginkgo peptides may be used for antihypertension.

Impacts of Industrial Modification on the Structure and Gel Features of Soy Protein Isolate and its Composite Gel with Myofibrillar Protein

Native soy protein isolate (N-SPI) has a low denaturation point and low solubility, limiting its industrial application. The influence of different industrial modification methods (heat (H), alkaline (A), glycosylation (G), and oxidation (O)) on the structure of SPI, the properties of the gel, and the gel properties of soy protein isolate (SPI) in myofibril protein (MP) was evaluated. The study found that four industrial modifications did not influence the subunit composition of SPI. However, the four industrial modifications altered SPI's secondary structure and disulfide bond conformation content. A-SPI exhibits the highest surface hydrophobicity and I_850/830 ratio but the lowest thermal stability. G-SPI exhibits the highest disulfide bond content and the best gel properties. Compared with MP gel, the addition of H-SPI, A-SPI, G-SPI, and O-SPI components significantly improved the properties of the gel. Additionally, MP-ASPI gel exhibits the best properties and microstructure. Overall, the four industrial modification effects may impact SPI's structure and gel properties in different ways. A-SPI could be a potential functionality-enhanced soy protein ingredient in comminuted meat products. The present study results will provide a theoretical basis for the industrialized production of SPI.

Alkali-Induced Phenolic Acid Oxidation Enhanced Gelation of Ginkgo Seed Protein

The effect of alkali-induced oxidation of three phenolic acids, namely gallic acid, epigallocatechin gallate, and tannic acid, on the structure and gelation of ginkgo seed protein isolate (GSPI) was investigated. A mixture of 12% (w/v) GSPI and different concentrations of alkali-treated phenolic acids (0, 0.06, 0.24, and 0.48% w/w) were heated at 90 °C, pH 6.0, for 30 min to form composite gels. The phenolic treatment decreased the hydrophobicity of the GSPI sol while enhancing their rheological properties. Despite a reduced protein solubility, water holding capacity, stiffness, and viscoelasticity of the gels were improved by the treatments. Among them, the modification effect of 0.24% (w/v) EGCG was the most prominent. Through the analysis of microstructure and composition, it was found to be due to the covalent addition, disulfide bond formation, etc., between the quinone derivatives of phenolic acids and the side chains of nucleophilic amino acids. Phenolic acid modification of GSPI may be a potential ingredient strategy in its processing.

Elastic and transparent ovalbumin hydrogels formed via succinylation combined with pH-shifting treatment

Ovalbumin (OVA) is a model protein with extensive research on structure and function, however, the application of OVA in food processing is limited due to its low gelation properties. In this study, thermally-induced highly transparent and elastic hydrogels from OVA pretreated by succinylation combined with pH-shifting method were reported. Transmission electron microscope (TEM) and free sulfhydryl groups determination revealed that the pretreatment induced the stretching of the protein structure and promoted the formation of preliminary aggregates. Further heating the pretreated OVA suspension resulted in a homogeneous and macroporous gel network with thin connecting walls. Such homogeneous gel network structures may be related to the effective modulation of the thermal aggregation efficiency of proteins by succinylation and the high level of protein unfolding by pH-shifting treatments, which synergistically allowed for more active sites to be created during heating to facilitate intermolecular interactions, including hydrogen bonding and hydrophobic interactions. Notably, the method resulted in a 507.14% increase in elasticity, a 60.74% increase in water holding capacity of the OVA hydrogels compared to the native OVA hydrogels without pretreatment. Also, the hydrogels were transparent with 73.11% light transmittance. In conclusion, succinylation and pH-shifting combined treatment could be an effective method for the preparation of OVA hydrogels with superior gelation properties.

Synergistic effects of pH shift and heat treatment on solubility, physicochemical and structural properties, and lysinoalanine formation in silkworm pupa protein isolates

The application of silkworm pupa protein isolates (SPPI) in food industry was limited because SPPI's solubility is poor and it contains a potential harmful component of lysinoalanine (LAL) which formed during protein extraction. In this study, combined treatments of pH shift and heating were performed to improve the solubility of SPPI and to reduce the content of LAL. The experimental results showed that the promoting effect on SPPI's solubility by alkaline pH shift + heat treatment was greater than that by acidic pH shift + heat. And an 8.62 times increase of solubility was observed after pH 12.5 + 80 ℃ treatment compared to the control SPPI sample which was extracted at pH 9.0 without pH shift treatment. Very strong positive correlation was found between alkali dosage and SPPI solubility (Pearson's correlation coefficient r = 0.938). SPPI with pH 12.5 shift treatment showed the highest thermal stability. Alkaline pH shift combined with heat treatment altered the micromorphology of SPPI and destroyed the disulfide bonds between macromolecular subunits (72 and 95 kDa), resulting in reduced particle size and increased zeta potential and free sulfhydryl content of the isolates. The fluorescence spectra analysis showed red shifts phenomena with pH increasing and fluorescence intensity increase with temperature increasing, implying the alterations in the tertiary structure of protein. Compared to the control SPPI sample, the amount of LAL reduced by 47.40 %, 50.36 % and 52.39 % using pH 12.5 + 70 ℃, pH 12.5 + 80 ℃ and pH 12.5 + 90 ℃ treatment, respectively. These findings provide fundamental information for the development and application of SPPI in food industry.

Effect of sodium trimetaphosphate on the physicochemical properties of modified soy protein isolates and its lutein-loaded emulsion

Due to people's pursuit of healthy and green life, soy protein isolate (SPI) is occupying a larger and larger market share. However, the low solubility of SPI affects its development in the field of food and medicine. This paper aimed to investigate the effects of sodium trimetaphosphate (STMP) on the functional properties and structures of phosphorylated SPI and its lutein-loaded emulsion. After modification by STMP, the phosphorus content of phosphorylated SPI reached 1.2-3.61 mg/g. Infrared spectrum and X-ray photoelectron spectrum analysis confirmed that PO₄ ^3- had phosphorylation with -OH in serine of SPI molecule. X-ray diffraction analysis showed that phosphorylation destroyed the crystal structure of protein molecules. Zeta potential value of phosphorylated SPI decreased significantly. When STMP addition was 100 g/kg, particle size of protein solution decreased to 203 nm, and solubility increased to 73.5%. Furthermore, emulsifying activity and emulsifying stability increased by 0.51 times and 8 times, respectively. At the same protein concentration (1%-3% [w/w]), lutein-loaded emulsion prepared by phosphorylated SPI had higher absolute potential and smaller particle size. The phosphorylated protein emulsion at 2% concentration had the best emulsion stability after storage for 17 days. PRACTICAL APPLICATION: Phosphorylation significantly improved the emulsifying properties and solubility of SPI. Phosphorylated SPI significantly improved the stability of lutein-loaded emulsion. It provides theoretical basis for the application of phosphorylated SPI as emulsifier in delivery system and broadens the development of lutein in food and medicine field.

Improvement in Emulsifying Capacity of Goose Liver Protein Treated by pH Shifting with Addition of Sodium Tripolyphosphate and Its Proteomics Analysis

Goose liver isolate treated by pH shifting and pH shifting/non-enzyme phosphorylation with goose liver isolate was used as a control. The functional property differences in the protein and proteins involved in the interfacial layer treated with pH shifting and non-enzyme phosphorylation were studied. Compared with the goose protein isolates (GPIs) at pH 7.0, the GPIs treated by pH shifting was not a good choice to be an emulsifier in a neutral environment, and non-enzyme phosphorylation inhibited the negative effects of pH shifting treatment and improved protein properties. The results of proteomics showed that the identified proteins in the interfacial layer belong to hydrophilic proteins. Non-enzyme phosphorylation increased the abundances of most proteins due to ion strength, including some phosphorylated proteins. Correlation analysis indicated that protein solubility was highly positively related with S₀, intrinsic fluorescence, total sulfhydryl, free sulfhydryl, A0A0K1R5T3, R0KA48, R0KFP7, U3J1L1, P01989, R0JSM9, and R0LAD1, and was also highly negatively related with particle size and R0M210, R0M714, and R0LFA3. The emulsifying activity index (EAI) demonstrated highly positive correlation with protein solubility, and was correlated with R0JKI4, R0KK84, R0L1Y3, R0LCM7, A0A068C605, and U3IW62.

Preparation and characterization of octenyl succinic anhydride-modified ginkgo seed starch with enhanced physicochemical and emulsifying properties

A quick preparation of octenylsuccinylated (OS)-ginkgo seed starch was proposed by lipase-coupling esterification within 30 min, and the physicochemical and emulsifying properties of OS-ginkgo seed starch were evaluated. High-performance liquid chromatography results revealed that ginkgolic acid in ginkgo seed starch was too low to be detected, which improved the biosafety and application range of OS-ginkgo seed starch. The degree of substitution (DS) of OS-ginkgo starch varied from 0.006 to 0.0169 depending on the lipase concentration increased from 0% to 1% (w/w, based on the volume of starch solution), and the reaction efficiency obtained the highest value of 68.5% at the lipase concentration of 1%. Fourier transform infrared spectra of OS-ginkgo seed starch confirmed ester carbonyl splicing in the starch molecular with the characteristic peaks at 1722 and 1567 cm^-1 . Scanning electron microscopy observations revealed that the esterification occurred mainly in the amorphous regions with slight morphological modification. X-ray diffractions suggested that no crystal change occurred on the starch granule. The thermal analysis revealed that OS-ginkgo seed starch showed a lower temperature and endothermic enthalpy for gelatinization, and presented enhanced and DS-dependent emulsifying properties and in vitro antidigestion properties. PRACTICAL APPLICATION: Results indicated that OS-ginkgo seed starch prepared by lipase-coupling esterification would be an alternative emulsion stabilizer for encapsulation and delivery of hydrophobic components. This study would provide an alternative method for the efficient and economical production of OS-ginkgo seed starch, thereby broadening its application in commercial exploitation.

Modifying the physicochemical properties, solubility and foaming capacity of milk proteins by ultrasound-assisted alkaline pH-shifting treatment

This study investigated the effects of different treatment of alkaline pH-shifting on milk protein concentrate (MPC), micellar casein concentrate (MCC) and whey protein isolate (WPI) assisted by the same ultrasound conditions, including changes in the physicochemical properties, solubility and foaming capacity. The solubility of milk proteins had a significant increase with gradual enhancement of ultrasound-assisted alkaline pH-shifting (p < 0.05), especially for MCC up to 99.50 %. Also, treatment made a significant decline in the particle size of MPC and MCC, as well as the turbidity of the proteins (p < 0.05). The foaming capacity of MPC, MCC, and WPI was all improved, especially at pH 11, and at this pH, the milk protein also showed the highest surface hydrophobicity. The best foaming capacity at pH 11 was the result of the combined effect of particle size, potential, protein conformation, solubility, and surface hydrophobicity. In conclusion, ultrasound-assisted pH-shifting treatment was found to be effective in improving the physicochemical properties and solubility and foaming capacity of milk proteins, especially MCC, with promising application prospect in food industry.

Effects of proteins on emulsion stability: The role of proteins at the oil-water interface

To obtain a stable protein-added emulsion system, researchers have focused on the design of the oil-water interface. This review discussed the updated details of protein adsorption behavior at the oil-water interface. We evaluated methods of monitoring interfacial proteins as well as their strengths and limitations. Based on the effects of structure on protein adsorption, we summarized the contribution of pre-changing methods to adsorption. In addition, the interaction of proteins and other surface-active molecules at the interface had been emphasized. Results showed that protein adsorption is affected by conformation, oil polarity and aqueous environments. The monitoring of interfacial proteins through spectroscopic properties in actual emulsion systems is an emerging trend. Pre-changing could improve the protein adsorption and the purpose of pre-changing of proteins is similar. In the interaction with other surface-active molecules, co-adsorption is desirable. By co-adsorption, the respective advantages can be exploited to obtain a more stable emulsion system.

A combined approach for modifying pea protein isolate to greatly improve its solubility and emulsifying stability

Pea protein-based delivery systems have drawn much attention in the food and pharmaceutical fields in recent years. However, its broad application faces great limitations because of the low solubility. Here, we present a novel and effective approach to overcome this difficulty and enhance the techno-functional characteristics, especially emulsifying stability, of the pea protein isolate (PPI). By combining pH-shifting with ultrasound and heating (PUH), we concluded that the solubility of PPI greatly increased from 29.5 % to 90.4 %, whereas its surface hydrophobicity increased from 1098 to 3706. This was accompanied by the changes of PPI structure, as shown by circular dichroism and scanning electron microscopy. In addition, the modified PPI was applied to stabilize sunflower oil-in-water emulsions. The droplet size of the emulsion with PUHP was reduced and its emulsion stability was significantly elevated. Taken together, we propose a novel combined approach to prepare modified PPI with high solubility and emulsion stability. We expect our method will have a wider application in modifying plant proteins and improving their industrial processing.

Effects of pH and Ionic Salts on the Emulsifying and Rheological Properties of Acorn Protein Isolate

This study was designed to evaluate the emulsifying and rheological properties of acorn protein isolate (API) in different pH mediums (pH 3, 7 and 9) and in the presence of ionic salts (1 M NaCl and 1 M CaCl2). API shows higher solubility in distilled water at pH 7, while at the same pH, a decrease in solubility was observed for API in the presence of CaCl2 (61.30%). A lower emulsifying activity index (EAI), lower stability index (ESI), larger droplet sizes and slight flocculation were observed for API in the presence of salts at different pHs. Importantly, CaCl2 treated samples showed relevantly higher EAI (252.67 m2/g) and ESI (152.67 min) values at all pH as compared to NaCl (221.76 m2/g), (111.82 min), respectively. A significant increase in interfacial protein concentration (4.61 mg/m2) was observed for emulsion at pH 9 with CaCl2, while the major fractions of API were observed in an interfacial layer after SDS-PAGE analysis. All of the emulsion shows shear thinning behavior (τc > 0 and n < 1), while the highest viscosity was observed for emulsion prepared with CaCl2 at pH 3 (11.03 ± 1.62). In conclusion, API, in the presence of ionic salts at acidic, neutral and basic pH, can produce natural emulsions, which could be substitutes for synthetic surfactants for such formulations.

A combination of alkaline pH-shifting/acidic pH and thermal treatments improves the solubility and emulsification properties of wheat glutenin

Glutenin has limited applicability in food industry due to poor water solubility and emulsifying properties. In this study, the physicochemical properties of glutenin were improved by combined treatments of alkaline pH-shifting or acidic pH with heating. The surface morphology, structure and physicochemical properties were measured during the modification process of glutenin. Results showed that the smaller square clusters and regular tubular fibrils were observed in modified glutenin and the α-helix proportion of the treated glutenin was finally increased to 59.90 ± 0.01%. Compared with untreated glutenin, the combined treatments of pH-shifting with heating as well as fibrillation process increased the solubility of glutenin by 21.3 and 3.5 times, respectively. Moreover, the treated glutenin showed excellent emulsifying stability (EAI: 50.84 ± 0.51 m²g^-1) and thermal stability (peak temperature increased from 109.58 to 149.05 °C). This study provides an informative basis for improving the physicochemical and functional properties of glutenin.