High-pressure induced physicochemical and functional modifications of low-density lipoproteins from hen egg yolk

High-pressure treatment represents a potential method to stabilize microbiologically agricultural raw materials that are sensitive to heat treatments. Low-density lipoproteins (LDL), the main contributors to the exceptional emulsifying properties of yolk, are particularly sensitive to heat treatment. In this study, high-pressure treatments have been performed on LDL, and their impact on LDL physicochemical and emulsifying properties has been assessed. LDL dispersions at two pH levels (pH 3 and 8) were treated at different pressure levels: 200, 400, and 600 MPa at 20 degrees C. LDL dispersion characteristics (solubility, aggregation, and protein denaturation) and LDL emulsifying properties (o/w 30:70 emulsions: droplet size, flocculation, and protein adsorption) of nontreated and high-pressure treated dispersions were compared. Solubility is not altered by high-pressure treatment whatever the pH, whereas aggregation and protein denaturation are drastically enhanced, in particular at pH 8. The effects of these modifications on LDL emulsifying properties are mainly a diminution of the flocculation (depletion and bridging) at this same pH. Finally, it seems that high-pressure treatment combined with an alkaline pH decreases droplet flocculation of LDL dispersions.     

咸蛋黄快速腌制过程中理化性质变化规律

该研究以新鲜蛋黄为原料,利用快速腌制模具,探究在咸蛋黄的上表面添加食盐单侧腌制过程中,食盐添加量和腌制时间对咸鸡蛋黄快速腌制过程中形貌特征和理化性质变化规律的影响。借助多种仪器分析手段对蛋黄腌制过程中形貌与物性的变化、水分及盐分的迁移规律进行了表征。低场核磁及成像结果表明：在腌制过程中,蛋黄中的水分不断向外迁移,含水率显著降低,当增加食盐的添加量和延长腌制时间,会加快水分的迁移速率;原子吸收结果表明：增加食盐添加盐量越多和腌制时间越长盐分迁移速率越快,质构、色差结果共同表明咸蛋黄腌制过程中,由于水分的向外迁移和盐分的向内渗入,使得蛋黄的蛋白质发生聚集使颜色加深;同时与市售整个腌制后分离的鸡蛋黄产品相比,当腌制时间为7d,添加盐量为3%;腌制时间为3d,添加盐量为5%时,所得的样品与市面的成品咸鸡蛋黄的感官品质及量化指标差异不显著（P<0.05）,为咸蛋黄单侧腌制技术提供理论的可行性。     

Preparation of novel functional oligophosphopeptides from hen egg yolk phosvitin

Novel hen egg phosvitin phosphopeptides (PPP) with molecular masses of 1-3 kDa were prepared from tryptic hydrolysis following partial alkaline dephosphorylation. The phosvitin treated with various NaOH concentrations (0.05-0.4 N) resulted in different dephosphorylated proteins ranging from 17.5 to 96.3% of phosphate retention. The protein was digested into 10-20 amino acid peptides with trypsin. Calcium-binding properties of PPP were compared with those of commercial casein phosphopeptides in vitro. The PPP with 35% phosphate retention is shown to be effective for enhancing calcium binding capacity and inhibiting the formation of insoluble calcium phosphate. The results provide potential novel functional oilgophosphopeptides as nutraceuticals.     

Protein components of low-density lipoproteins purified from hen egg yolk

To identify apoproteins present in purified low-density lipoproteins from hen egg yolk in relation with their emulsifying properties, they have been separated by SDS-PAGE. We identified two different proteins by liquid chromatography-tandem mass spectrometry analysis of the peptides obtained by the trypsin digestion of protein gel bands. Apovitellenin I was identified as a monomer and a dimer. Its amino acid sequence was totally confirmed, and molecular mass determination by liquid chromatography-mass spectrometry showed that it did not present post-translational modifications but only a slight heterogeneity by the loss of one or two amino acids at the C-terminal part of the protein. Apolipoprotein B was identified into seven bands corresponding to fragments resulting of a processing of the hen blood apo-B protein. The identity of the fragments was determined by the observation of the sequence coverage by trypsin peptides and the sequence alignment with homologous human blood apolipoprotein B-100.     

Competitive adsorption of proteins from total hen egg yolk during emulsification

In this article, the competitive adsorption of egg yolk proteins at oil/water interfaces during emulsification is studied. By using two-dimensional polyacrylamide electrophoresis and mass spectrometry, it was possible to characterize and identify adsorbing and non-adsorbing protein species. The egg yolk contains proteins with a wide range of molecular weights and pI. Lipoproteins adsorbed selectively throughout the pH range investigated. It is suggested that selectivity is determined by the average hydrophobic and hydrophilic domain lengths in the protein sequences where long average hydrophobic domain lengths result in high affinity for the interface and thus strong preferential adsorption.     

Antioxidative stress activity of oligophosphopeptides derived from hen egg yolk phosvitin in Caco-2 cells

The protective effects of hen egg yolk phosvitin phosphopeptides (PPPs) against hydrogen peroxide (H2O2)-induced oxidative stress were evaluated in an in vitro assay using human intestinal epithelial cells. Caco-2 cells were stimulated with 1 mM H2O2 for 6 h, and the secretion of IL-8, a proinflammatory mediator, was determined by ELISA as a biomarker of oxidative stress. The inhibition of H2O2-induced IL-8 secretion from Caco-2 cells was observed by pretreatment for 2 h with PPPs, but not with phosvitin. PPPs also suppressed the formation of malondialdehyde in H2O2-treated Caco-2 cells. Furthermore, intracellular glutathione levels and glutathione reductase activity were elevated by the addition of PPPs. The protective effects of PPPs against H2O2-induced oxidative stress were almost the same as that of glutathione, and PPPs with a high content of phosphorus exhibited higher protective activity than PPPs without phosphorus; however, phosphoserine itself did not show any significant antioxidative stress activity. These findings suggest that oligophosphopeptides from hen egg yolk phosvitin possess novel antioxidative activity against oxidative stress in intestinal epithelial cells and that phosphorus and peptide structure seem to have a key role in the activity.     

Effects of hen egg yolk immunoglobulin in passive protection of rainbow trout against Yersinia ruckeri

Anti-Yersinia ruckeri egg yolk immunoglobulin (IgY) was transferred to egg yolk after immunization of White Leghorn hens with formalin-killed whole cells of serovar 1 (RS1154) and serovar 2 (RS1153)Y. ruckeri and its lipopolysaccharide (LPS). The IgY was specific for its homologous LPS in western immunoblot, whereas some protein bands were commonly recognized, even by IgY from eggs of unimmunized hens. Purified LPS from both Y. ruckeri serovar types 1 and 2 had a very poor immunogenicity. The IgY activity was stable when processed into pellet form by a microbial transglutaminase treatment and showed a considerable resistance against acid pepsin for at least 2 h. Feeding specific anti-serovar 1 Y. ruckeri IgY to fish either before or after immersion infection produced marginal reductions in mortalities and in intestine infection. The same IgY did passively protect rainbow trout against infection when administered by intraperitoneal injection 4 h before an immersion challenge.     

Qualitative and quantitative liquid chromatographic analysis methods for the determination of the effects of feed supplements on hen egg yolk phospholipids

Quantitative and qualitative high-performance liquid chromatographic methods were utilized to separate phospholipid classes. After qualitative separation, the fatty acid moieties of each separated phospholipid class were determined using a gas chromatographic method. On the basis of these analyses, the effect of supplemented feeds on hen egg yolk lipids can be evaluated. The supplemented feeds contained 1-5% of vegetable-based or fish oils. The phospholipid content and composition were the same in all feeding groups, the proportions of phosphatidylcholines, phosphatidylethanolamines, and sphingomyelins being 70, 28, and 3%, respectively. In each feeding group, the fatty acid profiles of phosphatidylcholines and sphingomyelins were similar to each other and different from that of phosphatidylethanolamines. The supplemented feeds had a statistically significant (p < 0.05) effect on the fatty acid composition of phosphatidylcholines. The supplements decreased the proportion of saturated fatty acids in total fat, but this effect was not found in phospholipids.     

Metabolites of oxytetracycline, tetracycline, and chlortetracycline and their distribution in egg white, egg yolk, and hen plasma

4-epioxytetracycline and N-demethyloxytetracycline, as metabolites of oxytetracycline (OTC), 4-epitetracycline and N-demethyltetracycline, as metabolites of tetracycline (TC), and 4-epichlortetracycline, isochlortetracycline (ICTC), 4-epi-ICTC, and N-demethyl-ICTC, as metabolites of chlortetracycline (CTC), were detected in egg yolk and plasma obtained from feeding studies with either OTC, TC, or CTC. In egg white, only OTC, TC with its 4-epimer, and ICTC with its 4-epimer were detected in substantial concentrations. The ratios of epimerization and N-demethylation in the eggs did not change during the medication period. The samples were analyzed by an automated HPLC system (ASTED) with UV, fluorescence, or MS-MS detection.     

New insights into the structure of apolipoprotein B from low-density lipoproteins and identification of a novel YGP-like protein in hen egg yolk

Apoproteins of low-density lipoproteins (LDL) and soluble proteins (livetins) contained in hen egg yolk plasma have been demonstrated as being essential to the interfacial and emulsifying properties of yolk. The knowledge of their structure is necessary to better understand these properties. Purified protein fractions were separated by SDS-PAGE or 2D-PAGE and identified through the LC-MS/MS of their trypsin peptides. Hen blood apolipoprotein B gives rise to nine different apoproteins in LDL after maturation and proteolysis. Among these apoproteins, two protein fragments appeared to be less accessible to proteases and could be enriched in beta-sheets and firmly associated with lipids. Plasma soluble proteins were constituted by approximately 45% of yolk immunoglobulins with a high heterogeneity of the variable regions of both heavy and light chains, 41% of glycoproteins constituted by YGP42 and YGP40, 14% of albumins, and one new minor protein we called YGP30, showing 75% similarity to YGP40.     

Effect of cholecalciferol-enriched hen feed on egg quality

Eggs are one of the most important sources of vitamin D in the human diet, and their vitamin D content can be further increased by adding more vitamin D to hen feed. To investigate this issue more closely, we performed two feeding experiments. In both, zero egg samples were collected while the hens were fed regular feeds with a vitamin D content of 1720 or 4280 IU/kg. In experiment 1, egg samples were collected 2, 4, 7, 9, 11, 13, 16, 23, and 30 days after beginning the high-cholecalciferol (11 200 IU/kg) feeding period. In experiment 2, samples were collected 2, 4, 6, 8, 13, 28, 56, 84, 112, 140, and 168 days after beginning the high-cholecalciferol (12 000 IU/kg) diet. The egg samples were then assayed for their cholecalciferol content, and some samples, also for the presence of 25-hydroxycholecalciferol by an HPLC method. Further, the vitamin D-fortified eggs were compared with the controls by a sensory evaluation, by conducting fatty acid and functional analyses (emulsion capacity, gel forming capacity, foaming properties) and by measuring eggshell strength. Because vitamin D can be toxic in high doses, we also performed histopathological tests on the hens at the end of experiment 2. The top cholecalciferol contents in egg yolk (ca. 30 microg/100 g) were reached 8-13 days from starting the high-cholecalciferol diet. After 112 days feeding the cholecalciferol content gradually decreased to ca. 22 microg/100 g. When added to eggs as described above, vitamin D did not affect their sensory or functional properties or their fatty acid composition. Moreover, the cholecalciferol levels used in this study appeared not to affect eggshell strength or to be harmful for hens.     

Isolation and characterization of immunoglobulin in yolk (IgY) specific against hen egg white lysozyme by immunoaffinity chromatography

Six hens were intramuscularly (im) immunized once a week for 3 weeks using chicken egg white lysozyme (LS) as antigen. Antibody (immunoglobulin in yolk, IgY) ELISA values of 10(3)-fold diluted yolk were almost as high as 1.879 in the sixth week and maintained a value of 0.756 in the eighth week after the initial immunization treatment. The purification efficiency (specific activity of purified IgY against LS/specific activity of antibody in yolk against LS) of IgY specific against LS isolated by laboratory-prepared LS-bound (IgY-) Sepharose 4 Fast Flow immunoaffinity column was approximately 3380. By applying various amounts (0-22 mg) of the thusly obtained IgY specific against LS to the immunoaffinity column, the binding capacity (q(m)) and dissociation constant (K(d), M(-1)) of such immunoaffinity gel for IgY against LS were found to be 0.68 mg of IgY/mL of wet gel (0.54 mg of IgY/mg of LS) and 7.13 x 10(-6) M, respectively, as determined by Langmuir-type adsorption isotherms.     

Antimicrobial potential of egg yolk ovoinhibitor, a multidomain Kazal-like inhibitor of chicken egg

Chicken egg ovoinhibitor is a multidomain Kazal-type serine protease inhibitor with unknown function. Comparison of expression between different tissues indicated that ovoinhibitor is highly expressed in the magnum and liver followed by the uterus, which secrete egg white, egg yolk, and eggshell precursors, respectively. The results also revealed that ovoinhibitor expression is increased in the liver during sexual maturation followed by a subsequent decrease in mature hens. Ovoinhibitor was purified from the egg yolk plasma from nonfertilized eggs using two consecutive affinity chromatographies and gel filtration. Purified egg yolk ovoinhibitor was shown to inhibit trypsin and subtilisin. It was shown that purified egg yolk ovoinhibitor exhibited antimicrobial activities against Bacillus thuringiensis . The results suggest that this anti-protease plays a significant role in antibacterial egg defense against Bacillus spp., preventing contamination of table eggs (nonfertilized eggs) and protecting the chick embryo (fertilized eggs).     

Impact of surface-active compounds on physicochemical and oxidative properties of edible oil

The physical properties of lipids can have a major influence on lipid oxidation reactions. Edible oils contain surface-active compounds and water that can form physical structures such as reverse micelles. This study used the fluorescence probe, 5-dodecanoylaminofluorescein (DAF), to study both the physical and the chemical properties of stripped corn oil containing oleic acid and phosphatidylcholine. The fluorescence intensity of DAF increased with increasing water concentration in the edible oil. The addition of oleic acid decreased DAF fluorescence due to the ability of the free fatty acid to decrease the pH of the aqueous phase of the bulk oil. Phosphatidylcholine increased DAF fluorescence due to its ability to increase DAF exposure to the aqueous phase. Oleic acid had no impact on interactions between DAF and water-soluble peroxyl radicals, while phosphatidylcholine decreased peroxyl radical degradation of DAF. These results suggest that DAF could be a useful analytical tool to study the impact of the aqueous environment of bulk oil on lipid oxidation.     

Conjugated linoleic acids alter the fatty acid composition and physical properties of egg yolk and albumen

Effects of dietary conjugated linoleic acids (CLAs) and docosahexaenoic acid (DHA) on the fatty acid composition of different egg compartments after storage were studied. Four dietary treatments [supplemented with safflower oil (SAFF, control group), DHA, CLAs plus DHA (CAD), and CLAs alone] were administered to Single Comb White Leghorn (SCWL) laying hens. Eggs from the different treatment groups were collected and stored for 10 weeks at 4 degrees C before analysis. Fatty acids from the yolk (yolk granules and plasma), egg albumen, and vitelline membrane were analyzed by gas chromatography. The yolk of eggs from hens given CLAs had significantly higher amounts of saturated fatty acids, typically 16:0 and 18:0, but lower amounts of polyunsaturated fatty acids (PUFAs) compared to eggs from the control group (SAFF). CLA content was highest in the yolk and present in both neutral and polar lipids, with the greatest concentrations in neutral lipids. DHA was incorporated mainly into yolk polar lipids. Lipids in yolk plasma and granules contained similar amounts of CLAs. The fatty acid compositions of vitelline membrane and egg albumen mirrored that of the egg yolk. CLA supplementation resulted in hard and rubbery yolks when compared to hard-cooked eggs from the control group. This study showed that feeding CLAs to hens led to accumulation of the isomers in polar and neutral lipids of the egg yolk and that these isomers migrated into egg albumen. Because the sensory properties of hard-cooked eggs were negatively affected by the enrichment of a mixture of CLA isomers in this study, further research should be conducted to evaluate how the different isomers alter the properties of egg yolk and albumen so that the quality of designed eggs containing CLAs and DHA can be improved.     

Effect of steam pressure treatment on the physicochemical properties of Dioscorea starches

Dioscorea alata and Dioscorea rotundata starches were subjected to steam pressure treatments (0.35, 0.7, and 1.05 kg cm(-)(2)) for different periods. The total amylose content in the treated starches was not significantly affected, but the soluble amylose content decreased 3-5-fold. Reducing values and lambda(max) of the iodine complexes were unaffected. Viscosity of the starch paste was reduced by the treatments, and at higher pressures and longer time of treatments, the peak viscosity values were reduced to very low values. Pasting temperatures were enhanced considerably. Swelling volumes underwent reduction, but no change in solubility occurred. Clarity and paste stability were markedly lowered. The results suggest that starch granules are compressed by the steam pressure treatment, leading to vast changes in physicochemical properties.     

Effect of moisture content during dry-heating on selected physicochemical and functional properties of dried egg white

This article addresses the effect of moisture content (0.8-9.9%) during dry-heating (80 degrees C) on selected physicochemical (solubility, turbidity, residual denaturation enthalpy, aggregation, surface hydrophobicity, and sulfhydryl content) and functional (foaming ability, foam density, and stability) properties of freeze-dried egg white (FDEW). Moisture content during dry-heating proved to be a parameter determining the functionality of the resulting egg white powder. The degree of conformational changes induced in the egg white proteins by dry-heating was strongly dependent on the amount of water present. Preferentially, dry-heating at 80 degrees C should be performed on egg white powder with a moisture content below 6.8%, as the loss of protein solubility above this value is extensive. In addition to insoluble aggregates, soluble, strongly stabilized aggregates were also formed, especially at higher moisture contents. The decrease in denaturation enthalpy, increase in surface hydrophobicity, and exposure of SH groups previously hidden in the protein core and their subsequent oxidation were more pronounced at prolonged dry-heating times and at higher moisture contents. These conformational changes resulted in improved foaming ability and foams with lower density. No effect of dry-heating on the foam stability was observed.     

Identification and characterization of the precursor of chicken matrix metalloprotease 2 (pro-MMP-2) in hen egg

Using zymography and mass spectrometry, we identified for the first time the precursor of chicken matrix metalloprotease 2 (pro-MMP-2) as a complex with TIMP-2 (tissue inhibitor of metalloproteinases) in egg white and yolk. Real-time polymerase chain reaction confirmed that MMP-2 and its inhibitors TIMP-2 and TIMP-3 were expressed all along the oviduct and in the liver of laying hens. We also demonstrated that the processing of pro-MMP-2 into mature MMP-2 by serine proteases does not occur in vivo, although purified pro-MMP-2 undergoes proteolytic maturation by these proteases in vitro. Moreover, the relative pro-MMP-2 activity assessed by gelatin zymography was shown to decrease in egg white during the storage of unfertilized or fertilized eggs. However, the mature form of 62 kDa MMP-2 could not be detected. The fact that MMP-2 is found as a proform in fresh eggs suggests that the activity of this metalloprotease is regulated under specific conditions during embryonic development.     

Influence of a rare sugar, d-Psicose, on the physicochemical and functional properties of an aerated food system containing egg albumen

d-Psicose (Psi) might be an ideal sucrose (Suc) substitute for food products due to its sweet taste, easy processing, and functional properties (noncaloric and low glycemic response). In the present study, the effects of Psi on foaming properties of egg white (EW) protein and the quality of butter cookies were analyzed to find a better use of Psi in aerated food systems. The results showed that Psi could improve the foaming properties of EW protein with increasing whipping time in comparison to Suc and d-fructose (Fru). The addition of Psi to butter cookies, as partial replacement of Suc, had no influence on the cook loss while significantly contributing to a color change of the cookie crust through a nonenzymatic browning reaction. Furthermore, Psi-containing cookies possessed the highest antioxidant capacity in all tested cookies using two assays of radical scavenging activity and ferric reducing power. It was found that there was a close correlation between the crust color and the antioxidant activity of the cookie. The results suggest that the addition of Psi enhanced the browning reaction during cookie processing and, consequently, produced a strong antioxidant activity.     

Effects of soil moisture content on CO2 triggered soil physicochemical properties in a near-surface environment

Journal of Soils and Sediments - Carbon capture and storage (CCS) has been frequently discussed as a strategy for meeting CO2 emission reduction and its targets. However, some critical issues have...