Use of whey protein soluble aggregates for thermal stability-a hypothesis paper

The Influence of pH on the Emulsification Properties of Heated Whey Protein-Pectin Complexes

Interactions between proteins and polysaccharides could improve protein functional properties. Most studies focus on the formation of complex coacervates at pHs < pI. Much less attention has been given to the interactions at pHs > pI, especially when the mixtures are heated. The objective of this study was to investigate the emulsification properties of heated whey protein isolate (WPI) and pectin complexes formed at near neutral pHs. Heated soluble complexes (Cpxs) were formed by heating mixed WPI (3 wt% protein) and pectin (0 to 0.60 wt%) at pH 6.0, 6.5, or 7.0 at 85 °C for 30 min. Emulsions (5 wt% oil, 0.5 wt% protein, and pH 5.5) were characterized by measuring droplet size, zeta potential, rheological properties, and creaming stability. The results showed that, regardless of heating pH, Cpxs formed more stable emulsions with significantly smaller droplet sizes, higher negative charges, and less shear-thinning behavior in comparison to emulsions stabilized by heated WPI (p < 0.05). At fixed pectin concentrations, the emulsions stabilized by Cpx formed at pH 7.0 were the most stable. Increasing pectin concentrations led to a decrease in mean droplet sizes and an increase in negative charge. Maximum stability was achieved with the emulsion stabilized by Cpx formed with 0.60 wt% pectin at pH 7.0. The formation of Cpxs under proper conditions will allow for the utilization of WPI in a wider range of applications and fulfill the consumer need for clean label food products.

Dextran sulfate acting as a chaperone-like component on inhibition of amorphous aggregation and enhancing thermal stability of ovotransferrin

The tendency of ovotransferrin (OVT) to unfold and aggregate under 60 °C severely restricted sterilization temperature during egg processing. Searching for efficient strategies to improve OVT thermal stability is essential for improving egg product quality and processing suitability. Here, we investigated the effect of sulfate polysaccharide (dextran sulfate, DS) on heat-induced aggregation of OVT. We found that DS can effectively suppress amorphous aggregation of OVT at pH 7.0 after heating. Strikingly, the addition of 5 µM DS fully suppressed insoluble aggregates formation of 0.5 mg/mL OVT. Structure analysis confirmed that DS preserves nearly the entire secondary and tertiary structure of OVT during heating. The steric hindrance effect arising from strong electrostatic interactions between OVT and DS, coupled with reduced OVT hydrophobicity, is the underlying mechanism in suppressing protein-protein interactions, thus enhancing thermal stability. These findings suggest DS could act as protein stabilizers and chaperones, enhancing the thermostability of heat-sensitive proteins.

A comprehensive examination of ACE2 receptor and prediction of spike glycoprotein and ACE2 interaction based on in silico analysis of ACE2 receptor

The ACE2 receptor plays a vital role not only in the SARS-CoV-induced epidemic but also in various other diseases, including cardiovascular diseases and ARDS. While studies have explored the interactions between ACE2 and SARS-CoV proteins, comprehensive research utilizing bioinformatic tools on the ACE2 protein has been lacking. The one aim of present study was to extensively analyze the regions of the ACE2 protein. After utilizing all bioinformatics tools especially G104 and L108 regions on ACE2 were come forward. The results of our analysis revealed that possible mutations or deletions in the G104 and L108 regions play a critical role in both the biological functioning and the determination of the chemical-physical properties of ACE2. Additionally, these regions were found to be more susceptible to mutations or deletions compared to other regions of the ACE2 protein. Notably, the randomly selected peptide, LQQNGSSVLS (100-109), which includes G104 and L108, exhibited a crucial role in binding the RBD of the spike protein, as supported by docking scores. Furthermore, both MDs and iMODs results provided evidence that G104 and L108 influence the dynamics of ACE2-spike complexes. This study is expected to offer a new perspective on the ACE2-SARS-CoV interaction and other research areas where ACE2 plays a significant role, such as biotechnology (protein engineering, enzyme optimization), medicine (RAS, pulmonary and cardiac diseases), and basic research (structural motifs, stabilizing protein folds, or facilitating important inter molecular contacts, protein's proper structure and function).Communicated by Ramaswamy H. Sarma.

Improving myofibrillar proteins solubility and thermostability in low-ionic strength solution: A review

The development of myofibrillar proteins drinks (MPDs) can provide meat protein nutrition to specific groups of people. However, one major challenge is that myofibrillar proteins (MPs) are insoluble in solutions with a low ionic strength. Another functional constraint is the susceptibility of MPs to heat-induced aggregation. Currently, the primary approach used to improve the water solubility of MPs is to inhibit the assembly of myofilaments. Increasing the thermostability of MPs primarily inhibits the aggregation of myosin or oxidizes myosin to soluble substances. This review focuses on the description of several chemical and physical strategies, with an emphasis on the advantages, disadvantages, and recent progress. Under the myosin filament assembly process and the cross-linking aggregation mechanism, this summary helps improve our understanding of the solution and thermostability of MPs in low-ionic-strength solutions, thus providing new ideas to the development of MPDs.

In situ thermal modification of kafirin using infrared radiations and microwaves

BACKGROUND

Kafirin is a prolamin protein located in the corneous endosperm of sorghum. The conventional thermal processing of kafirin reduces its solubility, which limits its utilization in the food industry. Therefore, the study was aimed to investigate the effect of in situ thermal modification of kafirin using two different electromagnetic thermal treatments, namely infrared (IR) and microwave (MW) radiation, on the physicochemical, structural, thermal, and antioxidant properties.

RESULTS

The results demonstrated that both the thermal modifications improved yield, purity, and solubility of the kafirin with a decrease in hydrophobicity. However, IR-treated samples showed higher solubility (910.67 g kg^-1 ) and lower hydrophobicity (387.67). The IR modifications also improved the ratio of α helix/β sheets to a great extent. The alterations in the disulfide content were concomitant with the improvement in the thermal stability of kafirin. Sodium dodecyl sulfate polyacrylamide gel electrophoresis showed variations in the band intensities of β- and γ-kafirin, indicating alterations in the kafirin subunits. Morphological examination of kafirin revealed surface withering and agglomeration. Notably, IR treatment improved the antioxidant activity more efficiently (from 32.11% to 74.05%).

CONCLUSION

Although both the IR and MW treatments modified kafirin, the effect seemed to be more pronounced in IR modification. The IR-modified kafirin had better solubility and lesser hydrophobicity than MW-modified kafirin. The physicochemical and structural changes induced by IR treatment improved the biological activity of kafirin, in terms of antioxidant activity. Therefore, it was concluded that the in situ IR modification of kafirin can alter its characteristic properties, improving its potential as a food ingredient. © 2021 Society of Chemical Industry.

Physicochemical, structural and adhesion properties of walnut protein isolate-xanthan gum composite adhesives using walnut protein modified by ethanol

Low-sugar and high-protein adhesives have broad market application prospects, while natural plant proteins have confronted technical bottlenecks due to their poor adhesion. In this study, the effects of ethanol with different concentrations (0-80%) on the adhesion properties of walnut protein isolate-xanthan gum (WNPI-XG) composite adhesives were investigated. Results showed the bonding strength of WNPI-XG treated with 40% ethanol reached 12.55 MPa, the denaturation temperature and the surface hydrophobicity increased to 87.91 and 185.07 respectively, displaying the best rheological and texture properties. It also indicated appropriate concentration of ethanol (40%) didn't change the molecular weight of WNPI-XG, but greatly strengthened the fluorescence intensity, leading changes in contents of reactive sulfhydryl groups, electrostatic forces, hydrophobic interactions, hydrogen bonds and disulfide bonds. Furthermore, the treatment also facilitated a conformation conversion of the secondary structures from β-sheet to α-helix, promoting the full unfolding of protein molecules. The microstructure analysis showed after 40% ethanol treatment, the WNPI structure was uniform, the surface of WNPI-XG adhesive was flat and smooth, combined more closely with water molecules. By analyzing the influence of ethanol treatment on adhesion of WNPI-XG, the research laid a theoretical foundation for protein modification, providing good technical references for its development and utilization.

Effect of high pressure homogenization on aggregation, conformation, and interfacial properties of bighead carp myofibrillar protein

Fish myofibrillar protein is underutilized due to the formation of insoluble aggregates in low salt media. High pressure homogenization (HPH) at 20, 40, and 60 MPa for four passes was applied on bighead carp myofibrillar protein in order to modify its structure and interfacial properties. Changes in aggregation, conformation, solubility, emulsifying and foaming properties of myofibrillar protein were investigated. The aggregates of myofibrillar protein were obviously disrupted by HPH treatment. The size of myofibrillar protein aggregates became smaller and more uniform as the treating pressure increased, accompanied by notable decreases of cross-sectional height and Rq value in AFM image. Furthermore, the conformation of HPH-treated myofibrillar protein was unfolded into a flexible and open structure. α-helix and β-sheet were converted into β-turn and random coil. Surface hydrophobicity and zeta potential were strengthened, along with the exposure of sulfhydryl groups onto molecule surface. On the other hand, solubility, emulsifying activity index (EAI) and foaming capacity (FC) of HPH-treated myofibrillar protein were markedly enhanced with the increasing pressure. Especially after HPH treatment at 60 MPa, myofibrillar protein was almost dissolved in low salt media (solubility 91.86%) with 4.92 fold for EAI and 3.52 fold for FC. But there was little variation in emulsifying and foaming stabilities. These results suggested that HPH treatment has interesting potential to induce the dissociation and unfolding of myofibrillar protein in low salt media, therefore improving its interfacial properties. PRACTICAL APPLICATION: Carp myofibrillar protein was treated by high pressure homogenization (HPH). Aggregates of myofibrillar protein were disrupted into smaller size form. Conformation of myofibrillar protein was unfolded into open and loose structure. Emulsifying and foaming capacities of myofibrillar protein were improved. HPH treatment modified the structure and interfacial properties of myofibrillar protein.

Molecular Understanding of Fouling Induction and Removal: Effect of the Interface Temperature on Milk Deposits

Molecular details concerning the induction phase of milk fouling on stainless steel at an elevated temperature range were established to better understand the effect of temperature on surface fouling during pasteurization. The liquid-solid interface that replicates an industrial heat exchanger (≤75°C), including four stages (preheating, heating, holding, and cooling), was investigated using both a quartz crystal microbalance (QCM-D) and a customized flow cell. We found that the milk fouling induction process is rate-limited by the synergistic effects of bulk reactions, mass transfer, and surface reactions, all of which are controlled by both liquid and surface temperatures. Surface milk foulant becomes more rigid and compact as it builds up. The presence of protein aggregates in the bulk fluid leads to a fast formation of surface deposit with a reduced Young's modulus. Foulant adhesion and cohesion strength was enhanced as both interfacial temperature and processing time increased, while removal force increased with an increasing deposit thickness. During cleaning, caustic swelling and removal showed semilinear correlations with surface temperature (T_S), where higher T_S reduced swelling and enhanced removal. Our findings evidence that adsorption kinetics, characteristics of the foulant, and the subsequent removal mechanism are greatly dependent on the temperature profile, of which the surface temperature is the most critical one.

Impact of the Simulated Gastric Digestion Methodology on the In Vitro Intestinal Proteolysis and Lipolysis of Emulsion Gels

The aim of this work was to study the impact of the methodology of in vitro gastric digestion (i.e., in terms of motility exerted and presence of gastric emptying) and gel structure on the degree of intestinal proteolysis and lipolysis of emulsion gels stabilized by whey protein isolate. Emulsions were prepared at pH 4.0 and 7.0 using two homogenization pressures (500 and 1000 bar) and then the emulsions were gelled by heat treatment. These gels were characterized in terms of texture analysis, and then were subjected to one of the following gastric digestion methods: in vitro mechanical gastric system (IMGS) or in vitro gastric digestion in a stirred beaker (SBg). After gastric digestion, the samples were subjected to in vitro intestinal digestion in a stirred beaker (SBi). Hardness, cohesiveness, and chewiness were significantly higher in gels at pH 7.0. The degree of proteolysis was higher in samples digested by IMGS–SBi (7–21%) than SBg–SBi (3–5%), regardless of the gel’s pH. For SBg–SBi, the degree of proteolysis was not affected by pH, but when operating the IMGS, higher hydrolysis values were obtained for gels at pH 7.0 (15–21%) than pH 4.0 (7–13%). Additionally, the percentage of free fatty acids (%FFA) released was reduced by 47.9% in samples digested in the IMGS–SBi. For the methodology SBg–SBi, the %FFA was not affected by the pH, but in the IMGS, higher values were obtained for gels at pH 4.0 (28–30%) than pH 7.0 (15–19%). Our findings demonstrate the importance of choosing representative methods to simulate food digestion in the human gastrointestinal tract and their subsequent impact on nutrient bioaccessibility.

Gallic Acid-Aided Cross-Linking of Myofibrillar Protein Fabricated Soluble Aggregates for Enhanced Thermal Stability and a Tunable Colloidal State

Low colloidal stability of myofibrillar protein (MP) during heating is a technofunctional constraint encountered in its beverage application. Gallic acid (GA), a natural polyphenol, was applied to fabricate MP soluble aggregates for an enhanced thermal stability. Upon pH shifting, GA was grafted into MP with the cysteine and tryptophan residues being the binding sites. As a result, the antioxidant activity of MP was enhanced. Additionally, GA modification decreased the α-helix structure of MP and converted MP into cross-linked aggregates. At low dosages (10 and 25 μmol/g GA), disulfide-dominant covalent bonds were formed to generate myosin and actin aggregates, while MP aggregates were mostly bridged through GA-thiols or GA-tryptophan adducts when the dosages exceeded 50 μmol/g. Such aggregates prevented MP from thermal gelation, leading to a stable and tunable colloidal state. This work can foster technological advances in the tailor manufacture of muscle protein-based beverages for special dietary uses.

Modifying the Physicochemical and Functional Properties of Water-soluble Protein from Mussels by High-pressure Homogenization Treatment

This study investigated the changes in physicochemical and functional properties of water-soluble protein from mussels (MWP) induced by high-pressure homogenization (HPH). The results indicated that HPH treatment unfolded or disrupted the initial structure of MWP, exposing free sulfhydryl groups and buried hydrophobic groups. As the homogenization pressure increased, the aggregation of MWP particles gradually decreased. Moreover, protein solubility and dispersion stability increased in aqueous solution. Foaming and emulsifying properties were also improved. HPH treatment has proven to be an effective technique for enhancing the functional properties of shellfish protein, and 120 MPa was the optimum homogenization pressure to modify MWP.

The effect of heat treatment on the microstructure and functional properties of whey protein from goat milk

This work investigated the effects of thermal processing methods commonly used in the dairy industry and prolonged treatment at different temperatures on the denaturation, microstructure, and functional properties of whey proteins (WP) from goat milk. The complete denaturation of WP was observed in goat milk treated at 85°C for 30 min, and at a higher temperature (>85°C), a considerable amount of WP was easily denatured. The low temperature, long time treatment had the least effect on the secondary structure, whereas ultra-high temperature treatment had the greatest effect, and the amount of regular structures decreased gradually with prolonged time. The most serious morphological damage occurred after treatment at 85°C for 30 min, which was consistent with the denaturation results. This result indicated that the denaturation degree, particle size, surface hydrophobicity, and microstructure had a strong influence on the functional properties of WP from goat milk after heat treatment. The heat treatment of goat milk at 65°C for 30 min and 85°C for 15 s increased the particle size, turbidity, zeta potential, and surface hydrophobicity of WP, and these increases ensured that the WP had a good emulsifying activity index, water-holding capacity, oil-holding capacity, foaming capacity, and foam stability. This study simulated the heat treatment conditions used in actual production, aiming to provide a theoretical basis for industry.

Application of high-pressure homogenization for improving the physicochemical, functional and rheological properties of myofibrillar protein

The present work investigated effects of high-pressure homogenization (HPH) pressure (0, 40, 80 and 120 MPa) on physicochemical, functional and rheological properties of clam myofibrillar protein (CMP). Results showed that HPH changed the CMP secondary and tertiary structures. Absolute zeta potential and protein solubility increased but particle size and turbidity of CMP decreased after HPH treatment. Both of emulsifying properties and foaming properties were significantly improved. The shear stress, apparent viscosity and the viscosity coefficients reduced, but flow index increased. Application of HPH improved the physicochemical, functional and rheological properties of CMP, and 120 MPa was the optimal pressure for modification.

Systematical characterization of physiochemical and rheological properties of thermal-induced polymerized whey protein

BACKGROUND

Effects of pH (6-8), protein concentration (60-110, g kg^-1 ), heating temperature (70-95 °C) and time (5-30 min) on physiochemical and rheological properties of thermal-induced polymerized whey protein isolate (PWP) were systematically investigated. Degree of denaturation, particle size, zeta potential, free sulfhydryl group content, surface hydrophobicity and apparent viscosity were determined.

RESULTS

Heating whey protein above 75 °C at pH 7 or 8 resulted in denaturation of 80-90% whey protein. pH variation had a remarkable influence on particle size of samples (P < 0.05), whereas heating temperature and time did not generate significant changes. Zeta potential of PWP samples fell in the range of -30 to -40 mV. Free sulfhydryl group content of PWP samples decreased with increasing level regarding each factor. Surface hydrophobicity analysis showed that samples at higher pH or concentration became less hydrophobic, and increasing heating temperature or time resulted in higher hydrophobicity index. Time sweep test revealed that increasing protein concentration, heating temperature or time led to higher apparent viscosity. Flow behavior of PWP samples approached Newtonian character as protein concentration, heating temperature or time decreased.

CONCLUSION

Systematic data may provide helpful information in designing a heating process for dairy products and application of PWP in the food industry. © 2018 Society of Chemical Industry.

Cryptophane Nanoscale Assemblies Expand 129Xe NMR Biosensing

Cryptophane-based biosensors are promising agents for the ultrasensitive detection of biomedically relevant targets via 129Xe NMR. Dynamic light scattering revealed that cryptophanes form water-soluble aggregates tens to hundreds of nanometers in size. Acridine orange fluorescence quenching assays allowed quantitation of the aggregation state, with critical concentrations ranging from 200 nM to 600 nM, depending on the cryptophane species in solution. The addition of excess carbonic anhydrase (CA) protein target to a benzenesulfonamide-functionalized cryptophane biosensor (C8B) led to C8B disaggregation and produced the expected 1:1 C8B-CA complex. C8B showed higher affinity at 298 K for the cytoplasmic isozyme CAII than the extracellular CAXII isozyme, which is a biomarker of cancer. Using hyper-CEST NMR, we explored the role of stoichiometry in detecting these two isozymes. Under CA-saturating conditions, we observed that isozyme CAII produces a larger 129Xe NMR chemical shift change (δ = 5.9 ppm, relative to free biosensor) than CAXII (δ = 2.7 ppm), which indicates the strong potential for isozyme-specific detection. However, stoichiometry-dependent chemical shift data indicated that biosensor disaggregation contributes to the observed 129Xe NMR chemical shift change that is normally assigned to biosensor-target binding. Finally, we determined that monomeric cryptophane solutions improve hyper-CEST saturation contrast, which enables ultrasensitive detection of biosensor-protein complexes. These insights into cryptophane-solution behavior support further development of xenon biosensors, but will require reinterpretation of the data previously obtained for many water-soluble cryptophanes.

Systematical characterization of functional and antioxidative properties of heat-induced polymerized whey proteins

Effects of pH (6-8), protein concentration (6-11%, w/v), heating temperature (70-95 °C) and time (5-30 min) on functional and antioxidative properties of heat-induced polymerized whey protein were systematically investigated. All samples were determined for solubility at pH 4.6, emulsion capacity and stability, and antioxidative properties involving 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-azinobis(2-ethylbenzothiazoline-6-sulfonate) (ABTS) scavenging abilities. Heating resulted in significant loss in solubility, emulsion capacity and stability for whey protein, p < 0.05. Heating decreased DPPH but enhanced ABTS scavenging ability for whey protein significantly, p < 0.05. Changes caused by pH variation were much stronger than those observed for other factors. Both protein concentration and heating time had negative effects while heating temperature had positive effect on emulsion capacity of whey protein. Data indicates that functional and antioxidative properties of whey protein could be altered by factors including pH, protein concentration, heating temperature and time.

Water Soluble Self-Aggregates Induced Green Emission of Biocompatible Citric Acid-PEG Hyper Branched Polymer

An aliphatic citric acid-PEG hyper-branched polymer (CPHP) with a π-bond on the polymer backbone was synthesized by a single- step melt reaction in which the polymerization and π-bond formation occur simultaneously. The chemical structure of CPHP was confirmed by FTIR, 1H-NMR, 13C-NMR and MALDI-TOF mass spectral analyses. Aggregates are generally found to disperse in any solvent but the CPHP aggregates were soluble in water due to their hybrid nature. The π-bond in the aconitate unit induces green emission by CH/π interaction while the PEG unit of CPHP increases its solubility in water. The soluble aggregates induced green emission (SAIE) of the CPHP was investigated by UV-Visible absorption and emission spectra, time- correlated single photon counting (TCSPC) and zeta potential measurements. The fluorescence life time (τf) increased from 4.93 to11.38 ns with an increase in CPHP concentration. The fluorescence quantum yield (Φf) of CPHP can be altered by varying the concentration of CPHP.

Pepsin-Assisted Transglutaminase Modification of Functional Properties of a Protein Isolate Obtained from Industrial Sunflower Meal

The utilization of industrial sunflower meal to produce protein-rich products for the food industry is an alternative approach for better and more efficient use of this agricultural by-product. Sunflower meal proteins possess specific functional properties, which however need improvement to broaden their potential as supplements for delivering high--quality products for human nutrition. The aim of the study is to evaluate the combined influence of low-degree pepsin hydrolysis and transglutaminase (TG) modification on industrial sunflower meal protein isolate functionality at pH=2 to 10. Three TG-modified pepsin hydrolysates with the degree of hydrolysis of 0.48, 0.71 and 1.72% were produced and named TG-PH1, TG-PH2 and TG-PH3, respectively. All three TG-modified pepsin hydrolysates exhibited improved solubility at pH between 3.5 and 5.5 as the highest was observed of TG-PH3 at protein isoelectric point (pI=4.5). Sunflower meal protein isolate and TG-modified sunflower meal protein isolate had greater solubility than the three TG-modified hydrolysates at pH<3 and >7. Significant improvement of foam making capacity (p<0.05) was achieved with all three TG-modified pepsin hydrolysates in the entire pH area studied. Pepsin hydrolysis of the protein isolate with the three degrees of hydrolysis did not improve foam stability. Improved thermal stability was observed with TG-PH3 up to 80 °C compared to the protein isolate (pH=7). At 90 °C, TG modification of the protein isolate alone resulted in the highest thermal stability. Pepsin hydrolysis followed by a treatment with TG could be used to produce sunflower protein isolates with improved solubility, foam making capacity and thermal stability for use in the food industry.

Characterisation of heat-induced protein aggregation in whey protein isolate and the influence of aggregation on the availability of amino groups as measured by the ortho-phthaldialdehyde (OPA) and trinitrobenzenesulfonic acid (TNBS) methods

Whey protein isolate (WPI) solutions, with different levels of aggregated protein, were prepared by heating (5% protein, pH 7, 90°C for 30min) WPI solutions with either 20mM added NaCl (WPI+NaCl), 5mM N-ethylmaleimide (WPI+NEM) or 20mM added NaCl and 5mM NEM (WPI+NaCl+NEM). Gel electrophoresis demonstrated that the heated WPI and WPI+NaCl solutions had higher levels of aggregated protein, due to more covalent interactions between proteins, than the heated WPI+NEM and WPI+NaCl+NEM solutions. There were marked differences in the levels of amino groups between all heated WPI solutions when measured by the OPA and TNBS methods, with lower levels being measured by the TNBS method than by the OPA method. These results demonstrate that the measurement of available amino groups by the OPA method is less impacted than by the TNBS method after heat-induced structural changes, arising from disulfide or sulfhydryl-disulfide bond-mediated aggregation of whey protein molecules.