Effects of pH and different sugars on the structures and emulsification properties of whey protein isolate-sugar conjugates

The non-covalent and covalent interactions of whey proteins and saccharides: influencing factor and utilization in food

During the application of Whey proteins (WPs), they often have complex interactions with saccharides (Ss), another important biopolymer in food substrate. The texture and sensory qualities of foods containing WPs and Ss are largely influenced by the interactions of WPs-Ss. Moreover, the combination of WPs and Ss is possible to produce many excellent functional properties including emulsifying properties and thermal stability. However, the interactions between WPs-Ss are complex and susceptible to some processing conditions. In addition, with different interaction ways, they can be applied in different fields. Therefore, the non-covalent interaction mechanisms between WPs-Ss are firstly summarized in detail, including electrostatic interaction, hydrogen bond, hydrophobic interaction, van der Waals force. Furthermore, the existence modes of WPs-Ss are introduced, including complex coacervates, soluble complexes, segregation, and co-solubility. The covalent interactions of WPs-Ss in food applications are often formed by Maillard reaction (dry or wet heat reaction) and occasionally through enzyme induction. Then, two common influencing factors, pH and temperature, on non-covalent/covalent bonds are introduced. Finally, the applications of WPs-Ss complexes and conjugations in improving WP stability, delivery system, and emulsification are described. This review can improve our understanding of the interactions between WPs-Ss and further promote their wider application.

Effects of Different pH Levels on the Structural and Functional Properties of Proteins of Phaeodactylum tricornutum

Phaeodactylum tricornutum is identified by its capacity for rapid growth, reproduction, and in vitro cultivation, as well as the presence of a range of high-value active compounds, including proteins, with potential food applications. The objective of this study was to investigate the effects of pH shift treatments (pH of 3, 5, 7, 9, and 11) on the structural and functional properties of the Phaeodactylum tricornutum protein (PTP). The molecular weight of the PTP was predominantly distributed within the following ranges: below 5 kDa, 5-100 kDa, and above 100 kDa. Compared to the acidic environment, the PTP demonstrated higher solubility and greater free sulfhydryl group content in the alkaline environment. Additionally, PTP had a smaller particle size and higher thermal stability in alkaline environments. The PTP exhibited superior foaming ability (135%), emulsification activity index (3.72 m2/g), and emulsion stability index (137.71 min) in alkaline environments. The results of this investigation provide a foundation for the future development and application of the PTP in the food industry.

Euglena gracilis Protein: Effects of Different Acidic and Alkaline Environments on Structural Characteristics and Functional Properties

Due to the growing demand for human-edible protein sources, microalgae are recognized as an economically viable alternative source of proteins. The investigation into the structural characteristics and functional properties of microalgin is highly significant for its potential application in the food industry as an alternative source of protein. In this research, we extracted protein from Euglena gracilis by using alkaline extraction and acid precipitation and investigated its structural characteristics and functional properties in different acidic and alkaline environments. The molecular weight distribution of Euglena gracilis protein (EGP), as revealed by the size exclusion chromatography results, ranges from 152 to 5.7 kDa. EGP was found to be rich in hydrophobic amino acids and essential amino acids. Fourier infrared analysis revealed that EGP exhibited higher α-helix structure content and lower β-sheet structure content in alkaline environments compared with acidic ones. EGP exhibited higher foaming properties, emulsifying activity index, solubility, free sulfhydryl, and total sulfhydryl in pH environments far from its isoelectric point, and lower fluorescence intensity (2325 A.U.), lower surface hydrophobicity, larger average particle size (25.13 µm), higher emulsifying stability index, and water-holding capacity in pH environments near its isoelectric point. In addition, X-ray diffraction (XRD) patterns indicated that different acidic and alkaline environments lead to reductions in the crystal size and crystallinity of EGP. EGP exhibited high denaturation temperature (Td; 99.32 °C) and high enthalpy (ΔH; 146.33 J/g) at pH 11.0, as shown by the differential scanning calorimetry (DSC) results. The findings from our studies on EGP in different acidic and alkaline environments provide a data basis for its potential commercial utilization as a food ingredient in products such as emulsions, gels, and foams.

Stability of Protein Pharmaceuticals: Recent Advances

There have been significant advances in the formulation and stabilization of proteins in the liquid state over the past years since our previous review. Our mechanistic understanding of protein-excipient interactions has increased, allowing one to develop formulations in a more rational fashion. The field has moved towards more complex and challenging formulations, such as high concentration formulations to allow for subcutaneous administration and co-formulation. While much of the published work has focused on mAbs, the principles appear to apply to any therapeutic protein, although mAbs clearly have some distinctive features. In this review, we first discuss chemical degradation reactions. This is followed by a section on physical instability issues. Then, more specific topics are addressed: instability induced by interactions with interfaces, predictive methods for physical stability and interplay between chemical and physical instability. The final parts are devoted to discussions how all the above impacts (co-)formulation strategies, in particular for high protein concentration solutions.'

Structure, functional and physicochemical properties of lotus seed protein under different pH environments

BACKGROUND

The present study investigated the structure, functional and physicochemical properties of lotus seed protein (LSP) under different pH environments. The structures of LSP were characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, Fourier transform infrared spectroscopy (FTIR), zeta potential, particle size distributions, free sulfhydryl and rheological properties. The functional and physicochemical properties of LSP were characterized by color, foaming property, emulsification property, solubility, oil holding capacity, water holding capacity, differential scanning calorimetry analysis and surface hydrophobicity.

RESULTS

LSP was mainly composed of eight subunits (18, 25, 31, 47, 51, 56, 65 and 151 kDa), in which the richest band was 25 kDa. FTIR results showed that LSP had high total contents of α-helix and β-sheet (44.81-46.85%) in acidic environments. Meanwhile, there was more β-structure and random structure in neutral and alkaline environments (pH 7.0 and 9.0). At pH 5.0, LSP had large particle size (1576.98 nm), high emulsion stability index (91.43 min), foaming stability (75.69%) and water holding capacity (2.21 g g-1), but low solubility (35.98%), free sulfhydryl content (1.95 μmol g-1) and surface hydrophobicity (780). DSC analysis showed the denaturation temperatures (82.23 °C) of LSP at pH 5.0 was higher than those (80.10, 80.52 and 71.82 °C) at pH 3.0, 7.0 and 9.0. The analysis of rheological properties showed that LSP gel had high stability and great strength in an alkaline environment.

CONCLUSION

The findings of the present study are anticipated to serve as a valuable reference for the implementation of LSP in the food industry. © 2024 Society of Chemical Industry.

A curcumin oral delivery system based on sodium caseinate and carboxymethylpachymaran nanocomposites

The food industry has paid lots of attentions to curcumin because of its potential bioactive qualities. However, its use is severely constrained by its low bioavailability, stability and water solubility. Herein, we created sodium caseinate and carboxymethylpachymaran (CMP) nanoparticles (SMCNPs) that were loaded with curcumin. The composite nanoparticles were spherical, as characterized by SEM and TEM, the fluorescence spectroscopy, FTIR and XRD research revealed that hydrogen bonding, hydrophobic interaction and electrostatic interaction were the main drivers behind the creation of the nanoparticles. The SMCNPs exhibited lower particle size, greater dispersion and higher encapsulation rate when the mass ratio of sodium caseinate to CMP was 3:5 (particle size of 166.8 nm, PDI of 0.15, and encapsulation efficiency of 88.07 %). The composite nanoparticles had good antioxidant activity, physical stability and sustained release effect on intestinal tract during the in vitro simulation experiments, successfully preventing the early release of curcumin into gastric fluid. Finally, cytotoxicity studies told that the prepared composite nanoparticles have good biocompatibility and can inhibit the growth of tumor cells (HT-29). In conclusion, using CMP and sodium caseinate as carriers in this study may open up a fresh, environmentally friendly, and long-lasting way to construct a bioactive material delivery system.

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.

Comparison of ovalbumin glycation induced by high-temperature steaming and high-temperature baking: A study combining conventional spectroscopy with high-resolution mass spectrometry

High-temperature steaming (HTS) and high-temperature baking (HTB)-induced ovalbumin (OVA)-glucose glycation (140 °C, 1-3 min) were compared, and the different mechanisms were evaluated by changes in protein conformation, glycation sites and average degree of substitution per peptide molecule (DSP) values as well as the antioxidant activity of glycated OVA. Conventional spectroscopic results suggested that in comparison with HTB, HTS promoted protein expansion, increased β-sheet content and made OVA structure more orderly. Liquid chromatography-high resolution mass spectrometry (LC-HRMS) analysis showed that 10 glycation sites were found under HTB, while 4 new glycation sites R111, R200, R219 and K323 appeared under HTS, and 2 of them (R219 and K323) were located in internal β-sheet chains. The antioxidant activities of glycated OVA increased with increasing treatment time, and HTS showed stronger enhancement effect than HTB. Furthermore, the DSP values were generally higher under HTS than HTB. Compared with HTB, HTS with high penetrability could enhance the change of OVA primary structure and spatial conformation, making the protein structure more unfolded and stable, leading to more protein-sugar collisions occurred in inner OVA molecular and significantly promoted glycation. In conclusion, HTS is a promising method for high-temperature short-time glycation reaction, with drastically increasing the protein antioxidant activities.

Physicochemical and functional property of the Maillard reaction products of soy protein isolate with L-arabinose/D-galactose

BACKGROUND

Soy protein isolate (SPI) is widely used in the food industry because of its nutritional and functional properties. During food processing and storage, the interaction with co-existing sugars can cause changes in the structural and functional properties of SPI. In this study, SPI-l-arabinose conjugate (SPI:Ara) and SPI-d-galactose conjugate (SPI:Gal) were prepared using Maillard reaction (MR), and the effects of five-carbon/six-carbon sugars on the structural information and function of SPI were compared.

RESULTS

MR unfolded and stretched the SPI, changing its ordered conformation into disorder. Lysine and arginine of SPI were bonded with the carbonyl group of sugar. The MR between SPI and l-arabinose has a higher degree of glycosylation compared to d-galactose. MR of SPI enhanced its solubility, emulsifying property and foaming property. Compared with SPI:Ara, SPI:Gal exhibited better aforementioned properties. The functionalities of amphiphilic SPI were enhanced by MR, SPI:Gal possessed better hypoglycemic effect, fat binding capacity and bile acid binding ability than SPI:Ara. MR endowed SPI with enhanced biological activities, SPI:Ara showed higher antioxidant activities, and SPI:Gal exhibited stronger antibacterial activities.

CONCLUSION

Our work revealed that l-arabinose/d-galactose exhibited different effects on the structural information of SPI, and further affected its physicochemical and functional property. © 2023 Society of Chemical Industry.

Designing ultra-stable linseed oil-in-water Mickering emulsions using whey protein isolate cold-set microgels containing marjoram aqueous extract: Effect of pH and extract on rheological, physical, and chemical properties

In this study, whey protein isolate (WPI) cold-set microgels containing marjoram (Origanum majorana) aqueous extract (MAE) were prepared at different pHs (4.0, 5.0, and 6.0). After characterization, the microgel dispersion was used to stabilize linseed oil-in-water Mickering emulsions (MEs). The resultant MEs were then characterized in terms of physicochemical and rheological properties under the effect of pH and MAE addition. The morphology, particle size, zeta potential, and interfacial tension of microgels were affected by pH and MAE. XRD patterns showed the amorphous structure. Microgel-stabilized MEs did not reveal any significant sign of instability under gravity during 6 months of storage. All MEs had dominant elastic character. Despite the lowest zeta potential values, MEs prepared at pH 4 showed the highest physical stability against gravity but the lowest centrifugal stability against oiling off, which indicated that both viscous and elastic components are required for MEs stability. This sample had the highest apparent viscosity and the strongest viscoelastic properties. Rheological data were best fitted with Herschel-Bulkley and Power Law models. An increase in pH and presence of MAE improved the oxidative stability of MEs. The results of this study showed that WPI microgels are appropriate candidate for long-term stabilization of linseed oil-in-water MEs. The presence of MAE is useful in designing special emulsions in which the aqueous phase is partially replaced by the aqueous extract of medicinal plants.

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.

Food protein glycation: A review focusing on stability and in vitro digestive characteristics of oil/water emulsions

Recently, increasing studies have shown that the functional properties of proteins, including emulsifying properties, antioxidant properties, solubility, and thermal stability, can be improved through glycation reaction under controlled reaction conditions. The use of glycated proteins to stabilize hydrophobic active substances and to explore the gastrointestinal fate of the stabilized hydrophobic substances has also become the hot spot. Therefore, in this review, the effects of glycation on the structure and function of food proteins and the physical stability and oxidative stability of protein-stabilized oil/water emulsions were comprehensively summarized and discussed. Also, this review sheds lights on the in vitro digestion characteristics and edible safety of emulsion stabilized by glycated protein. It can further serve as a research basis for understanding the role of structural features in the emulsification and stabilization of glycated proteins, as well as their utilization as emulsifiers in the food industry.

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.

Effects of Glucose and Homogenization Treatment on the Quality of Liquid Whole Eggs

To investigate the effect of glucose on the protein structure, physicochemical and processing properties of liquid whole eggs (LWE) under homogenization, different concentrations of glucose (0.01, 0.02, 0.04, 0.08 g/mL) were added into LWE, followed by homogenizing at different pressures (5, 10, 20, 40 MPa), respectively. It was shown that the particle size and turbidity of LWE increased with the increase in glucose concentration while decreasing with the increase in homogenization pressure. The protein unfolding was increased at a low concentration of glucose combined with homogenization, indicating a 40.33 ± 5.57% and 165.72 ± 33.57% increase in the fluorescence intensity and surface hydrophobicity under the condition of 0.02 g/mL glucose at 20 MPa, respectively. Moreover, the remarkable increments in foaming capacity, emulsifying capacity, and gel hardness of 47.57 ± 5.1%, 66.79 ± 9.55%, and 52.11 ± 9.83% were recorded under the condition of 0.02 g/mL glucose at 20 MPa, 0.04 g/mL glucose at 20 MPa, and 0.02 g/mL glucose at 40 MPa, respectively. Reasonably, glucose could improve the processing properties of LWE under homogenization, and 0.02 g/mL–0.04 g/mL and 20–40 MPa were the optimal glucose concentration and homogenization pressure. This study could contribute to the production of high-performance and stable quality of LWE.

Glycosylation with bioactive polysaccharide obtained from Rosa roxburghii Tratt fruit to enhance the oxidative stability of whey protein isolate emulsion

Whey protein isolate (WPI) is an excellent source of emulsifier, but its function is limited for oxidative unstable in emulsion. In this study, WPI was glycated with Rosa roxburghii Tratt fruit polysaccharides (RTFP) by Maillard reaction under optimum conditions. The sodium dodecyl sulfate-polyacrylamide gel electrophoresis profile confirmed the formation of WPI-RTFP conjugates. The intrinsic fluorescence spectrum, CD and FT-IR indicated that the structure of WPI was affected after glycated with RTFP. In addition, the antioxidant activity of WPI-RTFP conjugates and WPI-RTFP emulsion were 3.5-fold and 1.5-fold stronger than that of WPI and WPI emulsion, respectively. Furthermore, the emulsion coated by conjugates demonstrated better oxidative stability than WPI with less peroxides produced after accelerated oxidation for 7 days. The results lay good foundation for the modification of protein by natural bioactive polysaccharides as well as for the application in healthy foods.

Improving physicochemical properties of myofibrillar proteins from wooden breast of broiler by diverse glycation strategies

The effect of diverse glycation strategies on the physicochemical and structural properties of wooden breast myofibrillar protein (WBMP) were studied. The WBMP was mixed with D-ribose (RI), sodium alginate (SA), and glucosamine (GH) respectively in a weight ratio of 1:2 (w/w) at 70 °C, and was heated for 6 h. Atomic force microscopy and particle size results showed that the glycation reaction in the presence of RI made WBMP to be more evenly dispersed in the solution and had a significantly smaller particle size (78-955 nm, average 361.06 nm) (P < 0.05). There was an increase in WBMP-RI solubility (76.23 ± 0.56%) and α-helix content (51.23 ± 1.1%) than other groups. Compared with WBMP-RI, WBMP-SA and WBMP-GH have poor performance in particle distribution, solubility and emulsification. This study clarified the aldehyde group in aldose was more suitable for the glycation modification of WBMP than the ketone group in ketose.

Comparison of the interfacial properties of native and refolded myofibrillar proteins subjected to pH-shifting

The emulsion abilities of pale, soft, exudative (PSE)-like chicken breast protein are unsatisfied, which are urgently needed to be ameliorated. This study evaluated the improvement of pH-shifting (11.0-, 11.5- and 12.0-7.0) on emulsion properties of the PSE-like chicken breast myofibrillar proteins (MPs) and the underlined structure-driven interfacial mechanism. It was found pH-shifting promoted the exposure of buried hydrophobic groups and free sulfhydryl groups, and changed secondary structures. Emulsions stabilized by refolded MPs exhibited more uniform and dispersed distributions with more adsorbed proteins at the interface. Electrophorogram showed both disulfide and non-disulfide covalent bonds were involved during interfacial protein-protein interaction. The results from circular dichroism and front-surface fluorescence spectroscopy revealed interfacial MPs were exposed to a more hydrophobic environment and increased β-sheets enhanced their molecular interactions. In addition, interfacial proteins after pH-shifting was less likely to be replaced by Tween 20.

Effects of Superheated Steam Treatment on the Allergenicity and Structure of Chicken Egg Ovomucoid

The aim of this study was to explore the effects of an emerging and efficient heating technology, superheated steam (SS), on the allergenicity and molecular structure of ovomucoid (OVM). OVM was treated with 120–200 °C of SS for 2 to 10 min. The allergenicity (IgG/IgE binding abilities and cell degranulation assay) and molecular structure (main functional groups and amino acids modification) changes were investigated. The IgG-binding ability of OVM decreased and the releases of β-hex and TNF-γ were inhibited after SS treatment, indicating that the protein allergenicity was reduced. Significant increases in oxidation degree, free SH content and surface hydrophobicity were observed in SS-treated OVM. The protein dimer and trimer appeared after SS treatment. Meanwhile, obvious changes occurred in the primary structure. Specifically, serine can be readily modified by obtaining functional groups from other modification sites during SS treatment. Moreover, the natural OVM structure which showed resistance to trypsin digestion was disrupted, leading to increased protein digestibility. In conclusion, SS-induced OVM aggregation, functional groups and amino acids modifications as well as protein structure alteration led to reduced allergenicity and increased digestibility.

Study on the emulsification and oxidative stability of ovalbumin-pectin-pumpkin seed oil emulsions using ovalbumin solution prepared by ultrasound

Pumpkin seed oil (PSO), which is a valuable compound with high nutritional value used for the prevention of various chronic diseases, is prone to oxidation. In this work, small and uniform (su) ovalbumin (OVA) and pectin (PEC) were used to stabilize PSO in the form of an emulsion. The results showed that suOVA-PEC-PSO emulsion with a droplet size of 9.82 ± 0.05 μm was successfully self-assembled from PSO, PEC, and suOVA solution (with a droplet size of 230.13 ± 14.10 nm) treated with 300 W ultrasound, owing to the formation of a more stable interfacial film on the surface of droplets. The interfacial, rheological, emulsifying, and antioxidant properties of the suOVA-PES-PSO emulsions were excellent, owing to the synergistic effects between PEC and suOVA solution. Moreover, the physical stability of the suOVA-PEC-PSO emulsions to salt stress, a freeze-thaw cycle, and heat treatment was also increased and the oxidation of linolenic acid was notably delayed. These results have extended the food-related applications of OVA and PSO, and provide a promising foundation for further exploration of the self-assembly of composite emulsions by small and uniform proteins.