Hydrophobic interaction adsorption of hen egg white proteins albumin, conalbumin, and lysozyme

Chicken egg white precipitates induced by water dilution

Chicken egg whites (whole egg white, EW; thick egg white, TKEW; thin egg white, TNEW) become turbid and are accompanied by the formation of precipitates after being diluted with an equal mass of deionized water. The precipitates of TKEW induced by water dilution (Thick Egg White Precipitates, TKEWP) account for 14.47 % of TKEW total dry matter, much higher than that of thin egg white precipitates (TNEWP) (1.51 %) and whole egg white precipitates (EWP) (5.53 %). Quantitative proteomic analysis identified 27 differentially abundant proteins (p < 0.05) among EW, EWP, TNEWP, and TKEWP. Lysozyme was found to be a key protein in the formation of EW precipitates induced by water dilution, as its abundance was significantly higher in TNEWP and TKEWP. Mucin-5B (α-ovomucin) had the highest abundance in TKEWP, suggesting that its insolubility is one of the important factors contributing to the large formation of TKEWP. This paper systematically studies the formation, characteristics, and composition of egg white precipitation caused by water dilution, and puts forward a new understanding of the processing characteristics of egg white liquid, thus laying a theoretical foundation for further research methods to reduce egg white precipitation by water dilution.

The enhanced properties and bioactivity of poly-ε-caprolactone/poly lactic-co-glycolic acid doped with carbonate hydroxyapatite-egg white

Synthetic polymers, such as PCL and PLGA, are among the main material choices in tissue engineering because of their stable structures and strong mechanical properties. In this study, we designed polycaprolactone (PCL)/polylactic-co-glycolate acid (PLGA) nanofibers doped with carbonate hydroxyapatite (CHA) and egg white (EW) with enhanced properties. The addition of CHA and EW significantly influenced the properties and morphology of PCL/PLGA nanofibers; whereby the CHA substitution (PCL/PLGA/CHA) greatly increased the mechanical properties related to the Young's modulus and EW doping (PCL/PLGA/CHA/EW) increased the elongation at break. Bioactivity tests of PCL/PLGA/CHA/EW after immersion in the SBF for 3 to 9 days showed increased fiber diameters and a good swelling capacity that could improve cell adhesion, while biocompatibility tests with NIH-3T3 fibroblast cells showed good cell proliferation (85%) after 48 h and antibacterial properties against S. aureus.

The pre-addition of "blocking" proteins decreases subsequent cellulase adsorption to lignin and enhances cellulose hydrolysis

The pre-adsorption of non-catalytic/blocking proteins onto the lignin component of pretreated biomass has been shown to significantly increase the effectiveness of subsequent enzyme-mediated hydrolysis of the cellulose by limiting non-productive enzyme adsorption. Layer-by-layer adsorption of non-catalytic proteins and enzymes onto lignin was monitored using Quartz Crystal Micro balancing combined with Dissipation monitoring (QCM-D) and conventional protein adsorption. These methods were used to assess the interaction between soft/hardwood lignins, cellulases and the three non-catalytic proteins BSA, lysozyme and ovalbumin. The QCM-D analysis showed higher adsorption rates for all of the non-catalytic proteins onto the lignin films as compared to cellulases. This suggested that the "blocking" proteins would preferentially adsorb to the lignin rather than the enzymes. Pre-incubation of the lignin films with blocking proteins resulted in reduced adsorption of cellulases onto the lignin, significantly enhancing cellulose hydrolysis.

Lysozyme impacts gel properties of egg white protein via electrostatic interactions, polarity differences, local pH regulation, or as a filler

The effects of lysozyme on egg white gel properties and their underlying causes were investigated under comparison between lysozyme removed with ion exchange resin and three levels of commercial lysozyme powder (1/2, 2/2, 3/2 the natural concentration in egg white) re-added in the lysozyme-removed system. Results showed that a lysozyme-removed gel obtained the best water holding capacity (61.61 %), lowest cooking loss (11.85 %), and enhanced textural properties (hardness, 638.04 g; resilience, 0.57; and gumminess), which was attributed to lysozyme promoting protein aggregation and weakening electrostatic repulsion by charge neutralization and competition for water, and this could be eliminated by removing lysozyme. Besides, the stronger intermolecular interactions (enhanced ionic bonds, hydrogen bonds and inhibited hydrophobic interactions), the shorter transverse relaxation time (T₂₁ and T₂₂), as well as more uniform microstructure formed in the lysozyme-removed gel, allowing the gels to bind more water molecules. With return of lysozyme, the gel properties were weakened to varying degrees, which was also ascribed to the filling of lysozyme in gel matrix narrowed interspace for binding and storage of water. In sum, adjustment on the content of lysozyme can regulate the gel properties of egg white, so as to obtain gels with regulable gel quality and processing characteristics.

Synthesis and Characterization of a New Cryogel Matrix for Covalent Immobilization of Catalase

The advantages of cryogels for enzyme immobilization applications include their mechanical and chemical robustness, ease of production, superior porosity, and low cost. Currently, many researchers are exploring porous material-based systems for enzyme immobilization that are more efficient and economically viable. Here, poly(2-Hydroxyethyl methacrylate-co-allyl glycidyl ether) (p(HEMA-co-AGE)) cryogel matrices were synthesized via the free radical cryopolymerization method to be employed as the support material. For the immobilization of the catalase enzyme onto the p(HEMA-co-AGE) cryogel matrix (catalase@p(HEMA-co-AGE), the best possible reaction conditions were determined by altering parameters such as pH, catalase initial concentration, and flow rate. The maximum catalase immobilization amount onto the p(HEMA-co-AGE) cryogel was found to be 48 mg/g cryogel. To determine the advantages of the cryogel matrix, e.g., the stability and reusability of the cryogel matrix, the adsorption–desorption cycles for the catalase enzyme were repeated five times using the same cryogel matrix. At the end of the reusability tests, it was found that the cryogel was very stable and maintained its adsorption capacity with the recovery ratio of 93.8 ± 1.2%. Therefore, the p(HEMA-co-AGE) cryogel matrix affords repeated useability, e.g., up to five times, without decreasing its catalase binding capacities significantly and has promising potential for many industrial applications. Cryogels offer clear distinctive advantages over common materials, e.g., micro/nano particles, hydrogels, films, and composites for these applications. At present, many researchers are working on the design of more effective and economically feasible, porous material-based systems for enzyme immobilization

Aldehydes as Wort Off-Flavours in Alcohol-Free Beers—Origin and Control

Although present in concentrations in microgrammes per litre level, aldehydes, in particular those derived from Strecker degradation, are known to majorly contribute to the undesired wort flavour of alcohol-free beers. In order to improve currently available products, one needs to understand the underlying cause for the over-prevalence and identify leverage points and methods to selectively reduce the aldehydes in alcohol-free beers. This work gives a short overview on relevant flavour-active wort flavours identified in alcohol-free beer and on their involved chemical formation pathways. Consequently, aldehyde removal technologies in general and in brewing industry are presented. Adsorptive removal of off-flavours by aldehyde-scavenging groups is already widely exploited in the packaging industry and may achieve reduction of these components to near depletion, depending on the process conditions. Its principles are adaptable to recovering off-flavours before filling. Also, supercritical CO2 extraction has been successfully applied to separate flavours from food matrices. In brewing, the focus has been set to biologic conversion by restricted fermentation steps, but the reduction of key components of more than 70% is not achieved. Newer developments focus on thermal separation techniques that not only include non-specific physical dealcoholisation but also more selective technologies such as pervaporation, where aldehydes are reduced to near depletion. However, for most unit operations, selectivity and capacity are not yet investigated. Future research should explore the shortcomings of current techniques and overcome bottlenecks either by developing more specific methods for aldehyde removal and/or a clever combination of unit operations to optimise the separation and process integration.

Complex coacervation between lysozyme and pectin: Effect of pH, salt, and biopolymer ratio

The complexation between lysozyme and pectin was studied by acidification using zeta potential, turbidity measurements and calorimetry titration. The complexes were analyzed in various NaCl concentrations with different ratios. At ratio 1:1 with 0.01M NaCl, is worth mentioning that the insoluble complexes were formed between pH 2.0 and 7.0, which represents a great range to apply this complex to different food matrices. When the ratio was increased from 1:1 to 3:1, the pH range between the pH_φ1 and pH_φ2 increased even more. When the NaCl concentration was increased from 0.01M to 0.2M, a progressive reduction of turbidity was observed. At 0.4M NaCl, there was total suppression of complex formation at ratio ≤ 3:1. The process of complex coacervate formation occurred in two different steps, presenting favorable enthalpic as well as entropic contributions. The positive entropy change is a strong indication that water molecules have been released from the complex surface, however the positive sign of TΔS suggests that hydrophobic interactions were involved in the interaction between lysozyme and pectin. Microscopy images of the samples revealed that the complexes presented a spheroid-like appearance which may contribute to possible future applications.

When the Label Matters: Adsorption of Labeled and Unlabeled Proteins on Charged Surfaces

Fluorescent labels are often attached to proteins to monitor binding and adsorption processes. Docking simulations for native hen egg white lysozyme (HEWL) and HEWL labeled with fluorescein isothiocyanate show that these adsorb differently on charged surfaces. Attachment of even a small label can significantly change the interaction properties of a protein. Thus, the results of experiments with fluorescently labeled proteins should be interpreted by modeling the structures and computing the interaction properties of both labeled and unlabeled species.

Recent advances for the production and recovery methods of lysozyme

Lysozyme is an antimicrobial peptide with a high enzymatic activity and positive charges. Therefore, it has applications in food and pharmaceutical industries as an antimicrobial agent. Lysozyme is ubiquitous in both animal and plant kingdoms. Currently, egg-white lysozyme is the most commercially available form of lysozyme. The main concerns of egg-white lysozyme are high recovery cost, low activity and most importantly the immunological problems to some people. Therefore, human lysozyme production has gained importance in recent years. Scientists have developed transgenic plants, animals and microorganisms that can produce human lysozyme. Out of these, microbial production has advantages for commercial productions, because high production levels are achievable in a relatively short time. It has been reported that fermentation parameters, such as pH, temperature, aeration, are key factors to increase the effectiveness of the human lysozyme production. Moreover, purification of the lysozyme from the fermentation broth needs to be optimized for the economical production. In conclusion, this review paper covers the mechanism of lysozyme, its sources, production methods and recovery of lysozyme.

Composite cryogels for lysozyme purification

Beads-embedded novel composite cryogel was synthesized to purify lysozyme (Lyz) from chicken egg white. The poly(hydroxyethyl methacrylate-N-methacryloyl-L-phenylalanine) (PHEMAPA) beads of smaller than 5 µm size were synthesized by suspension polymerization and then embedded into a poly(hydroxyethyl methacrylate) (PHEMA)-based cryogel column. The PHEMAPA bead-embedded cryogel (BEC) column was characterized by swelling tests, scanning electron microscopy (SEM), surface area measurements by the Brunauer-Emmett-Teller (BET) method, elemental analysis, and flow dynamics. The specific surface area of the PHEMAPA BEC was found as 41.2 m(2) /g using BET measurements. Lyz-binding experiments were performed using aqueous solutions in different conditions such as initial Lyz concentration, pH, flow rate, temperature, and NaCl concentration of an aqueous medium. The PHEMAPA BEC column could be used after 10 adsorption-desorption studies without any significant loss in adsorption capacity of Lyz. The PHEMAPA BEC column was used to purify Lyz from chicken egg white, and gel electrophoresis was used to estimate the purity of Lyz. The chromatographic application of the PHEMAPA BEC column was also performed using fast protein liquid chromatography.

Interaction of Quillaja bark saponins with food-relevant proteins

The surface activity and aggregation behaviour of two Quillaja bark saponins (QBS) are compared using surface tension, conductometry and light scattering. Despite formally of the same origin (bark of the Quillaja saponaria Molina tree), the two QBS show markedly different ionic characters and critical micelle concentrations (7.7·10(-6) mol·dm(-3) and 1.2·10(-4) mol·dm(-3)). The new interpretation of the surface tension isotherms for both QBS allowed us to propose an explanation for the previous discrepancy concerning the orientation of the saponin molecules in the adsorbed layer. The effect of three food-related proteins (hen egg lysozyme, bovine β-lactoglobulin and β-casein) on surface tension of the saponins is also described. Dynamic surface tension was measured at fixed protein concentrations and QBS concentrations varying in the range 5·10(-7)-1·10(-3) mol·dm(-3). Both dynamic and extrapolated equilibrium surface tensions of the protein/QBS mixtures depend not only on the protein, but also on the QBS source. In general, the surface tension for mixtures of the QBS with lower CMC and less ionic character shows less pronounced synergistic effects. This is especially well visible for β-casein/QBS mixtures, where a characteristic maximum in the surface tension isotherm around the molar ratio of one can be noticed for one saponin product, but not for the other.

Emulsifying and foaming properties of ultraviolet-irradiated egg white protein and sodium caseinate

The physicochemical and functional properties of ultraviolet (UV)-treated egg white protein (EW) and sodium caseinate (SC) were investigated. UV irradiation of the proteins was carried out for 30, 60, 90, and 120 min. However, the SC samples were subjected to extended UV irradiation for 4 and 6 h as no difference was found on the initial UV exposure time. Formol titration, SDS-PAGE, and FTIR analyses indicated that UV irradiation could induce cross-linking on proteins and led to improved emulsifying and foaming properties (P < 0.05). These results indicated that the UV-irradiated EW and SC could be used as novel emulsifier and foaming agents in broad food systems for stabilizing and foaming purposes.

Mechanism of hen egg white lysozyme adsorption on a charged solid surface

The mechanism of hen egg white lysozyme (HEWL) adsorption on a negatively charged, hydrophilic surface has been studied using atomistic molecular dynamics (MD) simulation. Sixteen 90 ns trajectories provide adequate data to allow a detailed description of the adsorption process to be formulated. Two distinct adsorption sites have been identified. The main one is located on the N,C-terminal protein face and comprises Arg128 (the crucial one), supplemented by Arg125, Arg5, and Lys1; the minor one is used accidentally and contains only Arg68. Adsorption of this protein is driven by electrostatics, where the orientation of the protein dipole moment defines the direction of protein movement. The diffusion range on the surface depends on protein side-chain penetration through the surface water layers. This is facilitated by the long-range electric field of the charged surface, which can align polar side chains to be perpendicular to the surface. A simulation of adsorption onto a neutral ionic surface shows no such surface water layer penetration. Therefore, protein flexibility is seen to be an important factor, and to adsorb the HEWL has to adjust its structure. Nevertheless, at a flat surface only a slight loss of α-helical content is required. The adsorbed HEWL molecule is oriented between side-on and end-on ways, where the angle between the protein long axis (which mostly approximates the dipole moment) and the surface varies between 45° and 90°. Simulations with targeted mutations confirm the picture that emerges from these studies. The active site is located on the opposite face to the main adsorption site; hence, the activity of the immobilized HEWL should not be affected by the surface interactions. Our results provide a detailed insight into the adsorption mechanism and protein mobility at the surface. This knowledge will aid the proper interpretation of experimental results and the design of new experiments and functional systems.

A new thermodynamic model describes the effects of ligand density and type, salt concentration and protein species in hydrophobic interaction chromatography

A new thermodynamic model is derived that describes both loading and pulse-response behavior of proteins in hydrophobic interaction chromatography (HIC). The model describes adsorption in terms of protein and solvent activities, and water displacement from hydrophobic interfaces, and distinguishes contributions from ligand density, ligand type and protein species. Experimental isocratic response and loading data for a set of globular proteins on Sepharose resins of various ligand types and densities are described by the model with a limited number of parameters. The model is explicit in ligand density and may provide insight into the sensitivity of protein retention to ligand density in HIC as well as the limited reproducibility of HIC data.