Effect of ultraviolet processing on selected properties of egg white

The effect of ultraviolet processing (10.6 and 63.7 kJ m(-2)) on selected properties of egg white (absorbance, particle size, protein fractions, free sulfhydryl content, immunoreactivity, viscosity, gelling and foaming properties) was investigated. Ultraviolet exposure induced the development of browning, the formation of large protein aggregates by disulfide exchange, and protein backbone cleavage. However, egg white proteins were differently sensitive to UV radiation. No changes in immunoreactivity, gelling temperature and gel firmness were observed. Independently on the UV dose, light treated egg white produced foams with higher stability. This effect was attributed to protein aggregates jamming in the fluid interstices between bubbles and/or to the higher viscosity of the aqueous phase. The latter was also associated to higher foam volume.     

Solubility and density of egg white proteins: Effect of pH and saline concentration

Influence of different pH values (3.0, 4.6, 6.0, 8.0 and 9.0) and salt concentrations (0.05, 0.1, 0.2, 0.35 and 0.5 mol/l) for three types of salt (NaCl, Na₂SO₄ and (NH₄)₂SO₄) on the solubility of egg white protein and density of egg white, at room temperature (25 °C) was studied. The results showed that the solubility of egg white protein was influenced by pH as well as concentration and type of salt present in the medium. Protein solubility increased with increase in pH, with higher solubility showed at pH 9.0 and lower solubility at pH 4.6. This behavior was verified for all the salts analysed. At acid pH (pH 3.0), it was observed the tendency of solubility elevation on the increase of the saline concentration, due to the salting-in effect. The density increased with increase in the salt concentration.     

Comparative effect of thermal treatment on the physicochemical properties of whey and egg white protein foams

The optimization of the functionalities of commercial protein ingredients still constitutes a key objective of the food industry. Our aim was therefore to compare the effect of thermal treatments applied in typical industrial conditions on the foaming properties of whey protein isolate (WPI) and egg white proteins (EWP): EWP was pasteurized in dry state from 1 to 5 days and from 60 °C to 80 °C, while WPI was heat-treated between 80 °C and 100 °C under dynamic conditions using a tubular heat exchanger. Typical protein concentrations of the food industry were also used, 2% (w/v) WPI and 10% (w/v) EWP at pH 7, which provided solutions of similar viscosity. Consequently, WPI exhibited a higher foamability than EWP. For WPI, heat treatment induced a slight decrease of overrun when temperature was above 90 °C, i.e. when aggregation reduced too considerably the amount of monomers that played the key role on foam formation; conversely, it increased foamability for EWP due to the lower aggregation degree resulting from dry heating compared to heat-treated WPI solutions. As expected, thermal treatments improved significantly the stability of WPI and EWP foams, but stability always passed through a maximum as a function of the intensity of heat treatment. In both cases, optimum conditions for foam stability that did not impair foamability corresponded to about 20% soluble protein aggregates. A key discrepancy was finally that the dry heat treatment of EWP provided softer foams, despite more rigid than the WPI-based foams, whereas dynamically heat-treated WPI gave firmer foams than native proteins.     

Novel peptides derived from egg white protein inhibiting alpha-glucosidase

The aim of this study was to search and identify potential anti-diabetic peptides with α-glucosidase and α-amylase inhibitory activities. After the Alcalase hydrolysis, egg white protein hydrolysates were purified and identified by LC–MS–MS. Eight identified peptides were further synthesized by the Fmoc solid-phase synthesis. The anti-diabetic activities of these synthetic peptides were assessed using enzymatic inhibitory assays against the α-glucosidase and α-amylase. Among the eight peptides, peptide RVPSLM was discovered as a potential α-glucosidase inhibitor with an IC₅₀ value at 23.07 μmol L⁻¹. However, it did not exhibit a visible or detectable inhibitory efficiency on the α-amylase. These studies indicate the potential of using egg white protein hydrolysates as a functional food product with the anti-diabetic activity.     

On hen egg fractionation: applications of liquid chromatography to the isolation and the purification of hen egg white and egg yolk proteins

Liquid chromatography has been used as a means of egg protein analysis or as a method for the purification of egg proteins. Several Chromatographic methods, including gel permeation, ion-exchange, reversed-phase, hydrophobic interaction, and immobilized-ligand-affinity chromatography, have been carried out for the separation or the purification of egg yolk or egg white proteins. Ion-exchange chromatography appears to be the most frequently used method for protein isolation and it is the easiest to adapt to a process scale. From an analytical point of view reversed-phase chromatography is, at the moment, the recommended method for egg white analysis. Egg white has been fractionated more often by liquid chromatography than has egg yolk. Several Chromatographic methods have been developed on a laboratory scale, but the application of these techniques on an industrial scale remains limited.     

Isolation and identification of angiotensin-converting enzyme inhibitory peptides from egg white protein hydrolysates

The aim of this study was to identify potential angiotensin I-converting enzyme (ACE) inhibitory peptide from egg white protein. The protein was hydrolysed by Alcalase and the hydrolysates were isolated with Gel filtration to get the high activity fraction. The fraction was identified by LC tandem mass spectrometric 4000 Q Trap MS. In the current work, 19 peptides were discovered in the fractions, five of which sourced from ovotransferrin and were synthesised by Fmoc solid phase method. ACE-inhibitory activity was measured by HPLC assay. The 50% inhibitory concentrations of Arg–Val–Pro–Ser–Leu (RVPSL) was 20 μM. Based on this remarkable ACE-inhibitory activity, it is suggested that RVPSL may have potential applications as a functional food, which could be used as nutraceutical compounds.     

Food properties of egg white protein modified by rare ketohexoses through Maillard reaction

d ‐psicose (Psi), a rare ketohexose, improves food properties of proteins through the Maillard reaction (MR) much more than d ‐fructose (Fru). This encouraged us to investigate the improvement of food properties of proteins through MR with various rare ketohexoses (d ‐psicose, Psi; d ‐tagatose, Tag; and d ‐sorbose, Sor). The food properties of egg white protein (EWP) after reaction with Psi, Tag, Sor and Fru were studied. Psi‐EWP (43.3 μmol TE g^?1) and Tag‐EWP (43.4 μmol TE g^?1) had the highest antioxidant activity, followed by Sor‐EWP (38.4 μmol TE g^?1) and Fru‐EWP (38.9 μmol TE g^?1). MR enhanced the breaking stress of heat‐induced EWP gels by 224–267%. The breaking stress was higher in Psi‐EWP (81.1 kN m^?2), Tag‐EWP (80.0 kN m^?2) and Sor‐EWP (77.8 kN m^?2) than in Fru‐EWP (71.6 kN m^?2). Furthermore, the foaming capacity was highest in Psi‐EWP and Sor‐EWP. Rare ketohexoses improved food properties of EWP more than Fru. Overall, Psi offered the greatest functional improvement.     

Effect of NaCl on thermal aggregation of egg white proteins from duck egg

Thermal aggregation of duck egg white solution (1 mg protein/ml, pH 7) was monitored in the presence of different NaCl concentrations (0–6%, w/w) across the temperature range of 20–90 °C. Duck egg white solution exhibited higher turbidity with coincidental increases in surface hydrophobicity and decreases in sulfhydryl group content as temperatures increased from 70 to 90 °C (p < 0.05). As NaCl concentration increased, the negative charge decreased, with coincidental increases in particle size of aggregate after heating to 90 °C. As visualised by confocal laser scanning microscopy, larger clusters of protein aggregates were observed with increasing NaCl concentrations. Major duck egg white protein with molecular mass of 45 kDa disappeared in the presence of 2–6% NaCl after heating above 80 °C, regardless of concentrations. Therefore, NaCl, especially at high concentrations, could induce thermal aggregation of duck egg white protein, which could determine the characteristics of salted egg white after heating.     

Probing the sol–gel transition of egg white proteins by pulsed-NMR method

The utility of pulsed NMR spectroscopy as a convenient means to monitor a sol–gel transition during heat-induced gelation of egg white proteins was investigated. This is based on the notion that, regardless of the mechanism of gel formation, the transition from sol to a gel state in such system is accompanied by the appearance of solid-like domain and a concomitant increase in the NMR signal attributed to protons in the solid-like fraction. The transition from sol to a gel state was clearly evident when the egg white was held isothermally at 80 °C in a water bath. The effects of some sugars and chemical cross-linking agents were also investigated in order to establish whether the method is capable of differentiating the relative effect of the chemicals on the kinetics of the gelation process. The results showed that pulsed NMR has a potential value as a complementary method to study sol–gel transition of food biopolymer.     

Primary and secondary structure of novel ACE-inhibitory peptides from egg white protein

The primary structure of novel angiotensin converting enzyme (ACE) inhibitory peptide from egg white protein was investigated, and secondary structure of the peptide was explored for the first time. The potential effects of bioactive peptides were submitted to bioactivity screening with ACE inhibitory activity, antioxidant property, and anticoagulation activity. Bioactive peptides from egg white protein were characterized by LC tandem mass spectrometric, and secondary structures of those peptides were investigated by FT-IR. Our results showed that total 11 bioactive peptides with three new and eight known structures were identified with LC/MS/MS, which then were synthesized by Fmoc solid phase method. Peptide Thr-Asn-Gly-Ile-Ile-Arg (TNGIIR) exhibited higher activity against ACE to other two new peptides. The concentration of the peptide TNGIIR, necessary to inhibit 50% the activity of ACE was 70 μM. Results also suggested that the secondary structural differences between peptides could also influence the ACE inhibition capacity. Thus, it appears that primary and secondary structure of peptide plays the potential role inhibiting the ACE activity.     

Effect of moisture content on selected physicochemical properties of two commercial hen egg white powders

After short-term storage at 23 °C, selected physicochemical properties of two hen egg white powders (with and without hydrolysis) were studied. Overall, the effect of moisture content on physicochemical properties of Hydrolysed Egg White powder (HEW) was more severe than those of Dried Egg White powder (DEW). The denaturation temperature (T_d) and its enthalpy change (ΔH_d) of ovalbumin in DEW followed an exponential model, as well as the T_d of HEW. The Gordon-Taylor equation modelled well the glass transition temperatures (T_g) of HEW and DEW. The Guggenheim-Anderson-de Boer (GAB) model fitted well to the type II moisture sorption isotherm. At the critical moisture content (12.0%, dry basis), compared with DEW, the colour of HEW began to darken dramatically and its hardness started to change significantly. These changes were closely related to the inherent characteristics of the two products. The mechanisms relevant to these physicochemical changes were discussed.     

Immunoreactivity of hen egg allergens: Influence on in vitro gastrointestinal digestion of the presence of other egg white proteins and of egg yolk

Hen egg white comprises of a complex mixture of proteins, which greatly differ in their physicochemical characteristics and relative abundance. We aimed to identify potential undiscovered egg allergens within the egg white proteome and investigated the existence of matrix effects on the proteolytic stability and resultant IgE-binding of the allergenic proteins. In addition to the main egg allergens: ovalbumin (OVA), ovomucoid (OM) and lysozyme (LYS), two minor egg white proteins, tentatively identified as ovoinhibitor and clusterin, were found to react with serum IgE from egg-allergic patients. Egg white exhibited residual immunoreactivity after gastrointestinal digestion due to the presence of intact OVA and LYS, as well as of several IgE-binding peptides derived from OVA. The presence of egg yolk slightly increased the susceptibility to hydrolysis of egg white proteins and abrogated bile salt-induced precipitation of LYS in the duodenal medium. However, the resultant immunoreactivity against IgE of egg white proteins after in vitro digestion was not significantly modified by the presence of yolk components.     

Dual mode diffusion and sorption of sodium chloride in pre-cooked egg white

The concentration profiles of NaCl by the one-dimensional diffusion in pre-cooked EW (egg white) were obtained at 5-80 °C. D's (Fick's diffusion coefficients) estimated at respective concentrations of NaCl in EW showed peaks at a certain NaCl concentration in the substrate. The peak became prominently high with the increase in temperature. These variations were interpreted in terms of the dual mode sorption and diffusion theory, which was successfully applied to the diffusion behavior of NaCl in Japanese radish. In EW, the water swollen protein phase coexists with the dispersed liquid water phase. It is in the former phase where the diffusion rate in EW is determined via the dual mode mechanism. By applying the theory, thermodynamic diffusion coefficients, D_T(p), of the partitioned species at respective temperatures were found to be smaller than those, D_T(L), of the Langmuir sorption species. The variations of D with peaks were interpreted with these two D_T's and equilibrium parameters of the two species. The sorption isotherms of NaCl by EW were found to be slightly convex upward at low NaCl concentrations, which were successfully interpreted by considering the two phases mentioned above and the equilibrium parameters for the partitioned and Langmuir species.     

大孔吸附树脂对蛋清蛋白水解物的吸附特性研究

为纯化蛋清蛋白质水解物以得到质量良好的产品，采用大孔吸附树脂对蛋清蛋白质水解液进行脱盐处理。对9种不同树脂进行了筛选实验，通过测定9种树脂的吸附率与解吸率衡量它们的性能，发现DA201-C型树脂的吸附率为80．85％，解吸率在70％酒精作为洗脱剂时为79．27％，两项指标皆优于其它树脂，从而筛选出最佳树脂为DA201-C型。为了阐明吸附行为的物化本质，进一步对吸附的静态吸附动力学与热力学性质进行了研究，结果表明：树脂对EWPH的吸附属于快速平衡型，且是吸热的物理吸附过程。     

Impact of pH on the interactions between whey and egg white proteins as assessed by the foamability of their mixtures

The impact of protein–protein interactions on foaming properties of mixtures consisting of egg white proteins (EWP) and whey proteins (WP) with total protein content of 60 g/L was examined at pH 5, 7 and 9. The ratio between EWP and WP in the mixtures was varied between 67:33, 50:50 and 33:67 (in %; w/w). The ionic strength was adjusted to that of milk (I = 176 mM). The foamability of the protein products was characterized by the foam capacity, stability and firmness. In addition, the hydrophobicity in the protein solutions was assessed as a measure for the physical behaviour and ability of proteins to adsorb at the air–water interface.The individual egg white proteins and whey proteins each showed the best foaming properties at pH 5 and pH 9, respectively. At pH 9 a synergism was observed in the capacity and stability of the foams from EWP/WP-mixtures. This effect appears to be caused by the electrostatic interactions between egg white and whey proteins which occur in the bulk solution after the pH adjustment prior to the foaming. In contrast, at pH 5 no positive influence of foaming the components in a mixture as well as no indication of intermolecular interactions was found. At pH value near the pI of ovalbumin the protein interactions occur when the proteins have adsorbed at the air–water interface. The protein systems foamed at pH 7 showed intermediate foamability compared to the values obtained at alkaline and acidic pH.     

Impact of food processing on the structural and allergenic properties of egg white

BackgroundEgg is one of the most nutritious foods that is easily available and it has become a favorite source of major nutrients like lipids and proteins around the world. However, eggs can trigger severe allergic reactions, especially in infants and children. The reactions are mostly IgE-mediated with a range of symptoms related to nose and throat and further can lead to life-threatening anaphylaxis. A total of ten allergens have been recognized to date and researchers are actively working on understanding their structure-function relationship which could help reduce the allergy incidences. Major egg allergens are abundant in egg white which include ovalbumin (OA), ovomucoid (OVM), ovotransferrin (OVT) and lysozyme (Lys). In addition to allergens, avidin present in egg white is also extensively studied due to its anti-nutritional properties. Avidin is known to form a complex with biotin which makes it unavailable for absorption.Scope and approachThis review focuses on the effects of thermal and non-thermal processing methods on the structure and functional properties of various egg proteins including a wide range of allergens and anti-nutrients.Key findings and conclusionsNovel processing techniques including various non-thermal techniques show promising results in reducing the allergic reactions of egg. Anti-nutrients like avidin can be partly inactivated under combined high-pressure processing and heat treatment.     

Functional properties of ovotransferrin from chicken egg white and its derived peptides: a review

Food Science and Biotechnology - With emerging trends in the food and pharmaceutical industries, potential applications of egg-derived bioactive compounds were recognized. Ovotransferrin is a major...     

Real-time monitoring of alcalase hydrolysis of egg white protein using near infrared spectroscopy technique combined with efficient modeling algorithm

The degree of hydrolysis is one of the most important indexes for process control and quality assessment in proteins enzymatic hydrolysis. This article proposed a simple and rapid near infrared spectroscopy method for real-time quantifying the degree of hydrolysis in alcalase hydrolysis process. Efficient variables selection algorithms were systemically studied in multivariate calibrations; the partial least squares coupled with uninformative variables elimination and ant colony optimization were proposed for modeling with results yielding Rp = 0.9525. Additionally, 10 independent samples with the relative error less than 10% further confirmed the stability and reliability of this method. This work demonstrated that the near infrared spectroscopy technique with a selected multivariate calibration has a high potential for in situ monitoring of alcalase hydrolysis process in protein industry.     

Functionality of egg white proteins as affected by high intensity ultrasound

The goal of this contribution was to determine the impact of HIUS on the thermal aggregation, gelation, foaming and emulsifying properties of egg white (EW) proteins.     

Effects of soy protein isolate and egg white solids on the physicochemical properties of gluten-free bread

Gluten-free formulations are often supplemented with proteins to improve their quality. To determine the effects of alternative proteins on a hydroxypropyl methylcellulose (HPMC)-treated gluten-free dough system, soy protein isolate was added at 1%, 2% and 3% while egg white solids were investigated at 5%, 10% and 15%. The formulated doughs were analysed using thermoanalytic and rheological techniques to determine the role of water and subsequent flow behaviour upon hydrocolloid addition. The baked loaves were measured for specific loaf volume and tensile strength to determine bread quality. The addition of soy protein isolate and egg white solids (5% and 10%) reduced dough stability by suppressing HPMC functionality, reducing available water, weakening HPMC interactions with the starch matrix and reducing foam stability. At 15% addition, egg white solids became the primary protein scaffolding in the dough and overcame negative interactions with HPMC, improving the loaf volume. However, this formulation may need further optimisation to meet full consumer acceptability.