Dual mode diffusion and sorption of sodium chloride in pork meats under cooking conditions

This study aims to obtain insight into mechanisms of NaCl diffusion in pork meats under cooking conditions: the loins at 5 (raw), 63 (pre-cooked) and 98 °C (pre-cooked), the mince at 98 °C (pre-cooked), and the filet at 98 °C (pre-cooked). It has been generally presumed that NaCl in any of pork meats diffuses with a constant Fick's diffusion coefficient, D, through liquid water channel imbibed in them. However in the present study, we experimentally obtained skewed bell shape variations of D in all of the above meats with respective maxima at certain low NaCl concentrations. These variations were interpreted in terms of a dual mode sorption and diffusion theory, which had been successfully applied to NaCl diffusion behaviors in Japanese radish and solidified egg white. This interpretation gives a thermodynamic diffusion coefficient, D_T(p) for the partition species of NaCl and another one, D_T(L) for the Langmuir type sorption species, both in the water swollen substrates in the meats. It was found that D_T(p) values are sizably smaller than corresponding D_T(L) values. This difference was ascribed to the lower water content in the p region than that in the L region. With the two D_Ts and additional equilibrium parameters, the theory explained the remarkable decrease of D value with C at 21 °C found by Guiheneuf et al. and nearly constant D values in the higher C range at 5 °C reported by other researchers. Experimentally obtained sorption isotherms of NaCl, which were slightly convex upward in the low C range, were satisfactorily reproduced with the parameters and the fractions of water swollen substrates in the whole meats.     

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.     

酶解卵清白蛋白条件的研究及其应用

对卵清白蛋白的最佳水解条件及水解液的应用进行了研究，结果表明：底物浓度5％，酶用量5000μ/g底物，反应温度50℃、反应初始pH5.0时，Flavourzyme对卵清白蛋白的水解度达55．1％，此条件下所获酶解液可制成富含多种氨基酸的白蛋白营养液。     

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.     

Tetracyclines and their metabolites in egg white and yolk

 4-Epimers of tetracycline (TC) and chlortetracycline (CTC) were formed in vivo in laying hens and excreted in substantial amounts besides the residues of the administered parent compounds via the egg. The recent observation of isochlortetracycline (i-CTC) and its 4-epimer as being the principal metabolites in eggs after feeding CTC could be confirmed. The ratio of 4-epimer to parent compound of TC, CTC and i-CTC was lower in egg white and higher in yolk and did not change during medication with TC or CTC. Further, yet unidentified, in vivo formed metabolites were observed. Received: 27 July 1998     

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.     

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.     

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.     

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.     

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.     

Dual mode diffusion of NaCl in Japanese radish under cooking conditions

ABSTRACT:  Sorption and diffusion of NaCl in Japanese radish have been studied. The sorption isotherm was obtained at 98 °C by the conventional method. The concentration profile by the 1-dimensional diffusion of NaCl in Japanese radish from the 3.0% solution was measured at 98 °C with the FRITRUC method involving a foodstuff rod in a thin rubber casing. Fick's diffusion coefficient, D , calculated therefrom showed a threefold variation with a maximum. This variation was quantitatively interpreted by applying a dual-mode sorption and diffusion theory under an assumption that the rate determining step of the diffusion is that in the cell wall. Two thermodynamic diffusion coefficients, D_T ( p ) and D_T ( L ), where p and L are the species of NaCl sorbed by partition and Langmuir modes, respectively, a parameter, α, derived from the local equilibrium relations between the p and L species, and S , the concentration of the Langmuir adsorption site in the cell wall of the radish, were estimated. D_T ( p ) was found to be smaller than D_T ( L ). As an explanation of the larger D_T ( L ), we invoked the higher hydration state of the adsorption site of the L species, being ascribed to residual anionic pectin in the radish than the local environment of the p species. The sorption isotherm showed a convex upward deviation from the linear relation. By using the parameters for the local equilibrium and some assumed parameters, the isotherm was found to be explainable. We suggest possible applications of the present method and interpretation to the diffusion study on the cooking systems comprising varieties of seasoning components and foodstuffs.     

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.     

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...     

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.     

Macromolecular crowding affects protein photosensitivity: The case of egg white immunoreactivity

An aqueous solution containing 0.1 g/l egg white proteins was exposed to increasing irradiance (0, 1.6, 7.2, 10.5, 17.0 and 29.1 W m⁻²) UV-C light for up to 30 min at 8 °C. In all cases, a decrease in immunoreactivity was detected. A 10-fold decrease of immunoreactivity was obtained in circa 7 min at 29.1 W/m² and in more than 4 h at 1.6 W/m². The loss of immunoreactivity was attributed to denaturation phenomena leading to the formation of protein fragments partially retaining the original epitopes. A progressive decrease in protein photosensitivity was observed by increasing its concentration. Above a limit concentration of 2.2 g/l, egg white proteins became extremely resistant to UV-light, even prolonging exposure time at 29.1 W/m² to 3 h. Photostability of egg white proteins was attributed to the occurrence of crowding effects which favoured protein folding and hindered photolysis.     

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.     

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 sugar, citric acid and egg white type on the microstructural and mechanical properties of meringues

Meringues are characterized by a predominant air phase and their overall quality is intimately related with microstructure. The formation of meringues microstructure relies on the capacity of egg white (EW) proteins to form voluminous and stable foams and it is ultimately related with the chemical properties of proteins and with the addition of ingredients such as sugars, salts, acids and surfactants.The study aimed at assessing the influence of sugar/EW ratio, citric acid and EW type on the microstructural and mechanical properties of meringues. Meringues prepared with different sugar/EW, citric acid level and different EW type were subjected to microstructural analysis by X-ray microtomography and to mechanical assessment by compression tests.Results demonstrate the ability of X-ray microtomography to reconstruct the 3D microstructure of meringues allowing the measurement of porosity, size, shape and distribution of pores. Citric acid, sugar concentration and EW type play a fundamental role on meringues microstructural parameters and mechanical properties. Low sugar/EW ratios as well as increasing citric acid levels increase the air phase and result in a softer texture of meringues. Moreover, low sugar/EW ratios and increasing citric acid in the meringue result in a reduction of pore size and also influence the shape of pores. Meringues microstructural and mechanical properties are affected by the EW quality: fresh and pasteurized EWs and EWs stored at refrigerated temperatures scored the highest structural and mechanical performances, while powdered and frozen EWs and albumens from old eggs showed the worst results. Not only the balance among ingredients but also the choice of raw materials can strongly affect the final quality of meringues.     

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.     

Antihypertensive,ACE-inhibitory and vasodilator properties of an egg white hydrolysate: Effect of a simulated intestinal digestion

In previous studies we showed that the egg white hydrolysate with pepsin (HEW) and its fraction with molecular mass lower than 3000 Da (HEW < 3000) have ACE-inhibitory activity in vitro and exert antihypertensive effects after single-oral and long-term administrations to spontaneously hypertensive rats (SHR). In this paper we have simulated an intestinal digestion on HEW and HEW < 3000 and addressed its effect on their ACE-inhibitory and vasodilator activities in vitro and antihypertensive activity in vivo. The results showed that the ACE-inhibitory activity of HEW and HEW < 3000 was maintained after the simulated intestinal digestion. HEW also exerted vasodilator activity in isolated aortic rings before and after the digestion. Both activities may explain the antihypertensive effects of these products in SHR. The peptides RADHP and YPI, which were detected by RP–HPLC–MS in the hydrolysates after the action of the pancreatic enzymes, could be responsible for the antihypertensive effects. In conclusion, HEW or HEW < 3000 could be useful in the prevention and/or treatment of hypertension and other associated disorders.