Yolk Lipoproteins Research Articles

Specific polyunsaturated fatty acids modulate lipid delivery and oocyte development in C. elegans revealed by molecular-selective label-free imaging.

Polyunsaturated fatty acids (PUFAs) exhibit critical functions in biological systems and their importance during animal oocyte maturation has been increasingly recognized. However, the detailed mechanism of lipid transportation for oocyte development remains largely unknown. In this study, the transportation of yolk lipoprotein (lipid carrier) and the rate of lipid delivery into oocytes in live C. elegans were examined for the first time by using coherent anti-Stokes Raman scattering (CARS) microscopy. The accumulation of secreted yolk lipoprotein in the pseudocoelom of live C. elegans can be detected by CARS microscopy at both protein (~1665 cm−1) and lipid (~2845 cm−1) Raman bands. In addition, an image analysis protocol was established to quantitatively measure the levels of secreted yolk lipoprotein aberrantly accumulated in PUFA-deficient fat mutants (fat-1, fat-2, fat-3, fat-4) and PUFA-supplemented fat-2 worms (the PUFA add-back experiments). Our results revealed that the omega-6 PUFAs, not omega-3 PUFAs, play a critical role in modulating lipid/yolk level in the oocytes and regulating reproductive efficiency of C. elegans. This work demonstrates the value of using CARS microscopy as a molecular-selective label-free imaging technique for the study of PUFA regulation and oocyte development in C. elegans.

Iron Overload Coordinately Promotes Ferritin Expression and Fat Accumulation in Caenorhabditis elegans.

The trace element iron is crucial for living organisms, since it plays essential roles in numerous cellular functions. Systemic iron overload and the elevated level of ferritin, a ubiquitous intracellular protein that stores and releases iron to maintain the iron homeostasis in cells, has long been epidemiologically associated with obesity and obesity-related diseases. However, the underlying mechanisms of this association remain unclear. Here, using Caenorhabditis elegans, we show that iron overload induces the expression of sgk-1, encoding the serum and glucocorticoid-inducible kinase, to promote the level of ferritin and fat accumulation. Mutation of cyp-23A1, encoding a homolog of human cytochrome P450 CYP7B1 that is related to neonatal hemochromatosis, further enhances the elevated expression of ftn-1, sgk-1, and fat accumulation. sgk-1 positively regulates the expression of acs-20 and vit-2, genes encoding homologs of the mammalian FATP1/4 fatty acid transport proteins and yolk lipoproteins, respectively, to facilitate lipid uptake and translocation for storage under iron overload. This study reveals a completely novel pathway in which sgk-1 plays a central role to synergistically regulate iron and lipid homeostasis, offering not only experimental evidence supporting a previously unverified link between iron and obesity, but also novel insights into the pathogenesis of iron and obesity-related human metabolic diseases.

Metabolome and proteome changes with aging in Caenorhabditis elegans

To expand the understanding of aging in the model organism Caenorhabditis elegans, global quantification of metabolite and protein levels in young and aged nematodes was performed using mass spectrometry. With age, there was a decreased abundance of proteins functioning in transcription termination, mRNA degradation, mRNA stability, protein synthesis, and proteasomal function. Furthermore, there was altered S-adenosyl methionine metabolism as well as a decreased abundance of the S-adenosyl methionine synthetase (SAMS-1) protein. Other aging-related changes included alterations in free fatty acid levels and composition, decreased levels of ribosomal proteins, decreased levels of NADP-dependent isocitrate dehydrogenase (IDH1), a shift in the cellular redox state, an increase in sorbitol content, alterations in free amino acid levels, and indications of altered muscle function and sarcoplasmic reticulum Ca2+ homeostasis. There were also decreases in pyrimidine and purine metabolite levels, most markedly nitrogenous bases. Supplementing the culture medium with cytidine (a pyrimidine nucleoside) or hypoxanthine (a purine base) increased lifespan slightly, suggesting that aging-induced alterations in ribonucleotide metabolism affect lifespan. An age-related increase in body size, lipotoxicity from ectopic yolk lipoprotein accumulation, a decline in NAD+ levels, and mitochondrial electron transport chain dysfunction may explain many of these changes. In addition, dietary restriction in aged worms resulting from sarcopenia of the pharyngeal pump likely decreases the abundance of SAMS-1, possibly leading to decreased phosphatidylcholine levels, larger lipid droplets, and ER and mitochondrial stress. The complementary use of proteomics and metabolomics yielded unique insights into the molecular processes altered with age in C. elegans.

Phase separation behavior of egg yolk suspensions after anionic polysaccharides addition

The objectives of this study were to understand the interactions between three anionic polysaccharides (gum arabic, xanthan gum and ι-carrageenan) and egg yolk at pH 3, 5, 6, 8, 10 and possible phase separation behavior. Zeta potential of egg yolk was not affected by gum arabic addition while it became more negative at pH 5 after xanthan gum and ι-carrageenan addition. The particle size of ι-carrageenan yolk suspension was considerably higher than the other polysaccharide yolk suspensions at pH below 6 but was dramatically decreased at alkaline pH. Most polysaccharide yolk suspensions formed either a biphasic or a monophasic system, whereas three distinct phases were observed for xanthan gum yolk suspension at pH 6. Protein profile analysis of the lipid-rich cream phase obtained from xanthan gum added yolk showed similarities to apoproteins from low density lipoproteins (LDL) of egg yolk. Microscopy analysis indicated the co-presence of xanthan gum and LDL in the creamy phase, within a network formed by xanthan gum. It was suggested that electrostatic and hydrophobic interactions between the egg yolk and xanthan gum as well as xanthan gum's rheological properties could be responsible for the unique phase separation observed in the study. The findings of this study can form the basis for future studies to develop a new method to separate LDL from egg yolk.

Supplementation of different concentrations of Orvus Es Paste (OEP) to ostrich egg yolk lipoprotein extender improves post-thaw boar semen quality.

This study aimed to compare post-thaw quality of boar semen following freezing in an ostrich egg yolk lipoprotein (LPFo) extender supplemented with 0%, 0.25% and 0.50% Orvus Es Paste (OEP). Sperm assessments included total motility (TMOT), mitochondrial function (MF), plasma membrane integrity (PMI) and acrosome integrity (normal apical ridge, NAR). Considerable variations among boars and OEP treatments had a significant effect (P < 0.001) on post-thaw sperm characteristics. It was observed that post-thaw sperm characteristics were significantly compromised in semen samples frozen in the absence of OEP. By contrast, lactose-LPFo-glycerol extender supplemented with either 0.25% OEP or 0.50% OEP markedly enhanced post-thaw sperm characteristics. In all boars, there were no marked differences in post-thaw sperm TMOT between the freezing extenders supplemented with 0.25% and 0.50% OEP. However, a decline in the percentage of post-thaw motile spermatozoa was more pronounced in the extender supplemented with 0.50% OEP following a 120-min incubation period. Furthermore, the proportions of frozen-thawed spermatozoa with MF, PMI and NAR acrosomes varied significantly among the boars in the OEP-supplemented extenders. The findings of this study indicate that different OEP concentrations, in the presence of ostrich egg yolk lipoproteins, could have varying effects on post-thaw sperm survival.

Lipid droplet pattern and nondroplet-like structure in twofatmutants ofCaenorhabditis elegansrevealed by coherent anti-Stokes Raman scattering microscopy

Lipid is an important energy source and essential component for plasma and organelle membranes in all kinds of cells. Coherent anti-Stokes Raman scattering (CARS) microscopy is a label-free and nonlinear optical technique that can be used to monitor the lipid distribution in live organisms. Here, we utilize CARS microscopy to investigate the pattern of lipid droplets in two live Caenorhabditis elegans mutants (fat-2 and fat-3). The CARS images showed a striking decrease in the size, number, and content of lipid droplets in the fat-2 mutant but a slight difference in the fat-3 mutant as compared with the wild-type worm. Moreover, a nondroplet-like structure with enhanced CARS signal was detected for the first time in the uterus of fat-2 and fat-3 mutants. In addition, transgenic fat-2 mutant expressing a GFP fusion protein of vitellogenin-2 (a yolk lipoprotein) revealed that the enhanced CARS signal colocalized with the GFP signal, which suggests that the nondroplet-like structure is primarily due to the accumulation of yolk lipoproteins. Together, this study implies that CARS microscopy is a potential tool to study the distribution of yolk lipoproteins, in addition to lipid droplets, in live animals.

Fluorescent nanodiamond as a probe for the intercellular transport of proteins in vivo

This study investigates the intercellular transport of yolk lipoproteins in Caenorhabditis elegans by using fluorescence lifetime imaging microscopy (FLIM) and fluorescent nanodiamonds (FNDs) as photostable labels and tracers. The yolk lipoproteins in the nematode are similar to human serum low-density lipoproteins (LDLs), serving as an intercellular transporter of fat molecules and cholesterol. To study this fundamentally important process, FNDs were first coated with yolk lipoprotein complexes (YLCs) and then microinjected into the intestinal cells of the living organism. Real-time imaging over a time period of more than 50 min with FLIM revealed the process of YLC-FND secretion from the intestine to the pseudocoelomic space, followed by transporting into oocytes and subsequent accumulation in the multi-cellular embryos derived from the oocytes. Colocalization studies of the rme-2 adult hermaphrodites expressing green fluorescent protein (GFP)-tagged YLCs confirmed that the injected YLC-FNDs were taken up by oocytes through endocytosis mediated by the LDL receptor, RME-2, functioning as an YLC receptor. Our results demonstrate that FND is useful as a biomolecular nanocarrier without significantly altering the functionality of the cargos for intercellular transport, cell-specific targeting, and long-term imaging applications in vivo.

A Heterogeneous Mixture of F-Series Prostaglandins Promotes Sperm Guidance in the Caenorhabditis elegans Reproductive Tract

The mechanisms that guide motile sperm through the female reproductive tract to oocytes are not well understood. We have shown that Caenorhabditis elegans oocytes synthesize sperm guiding F-series prostaglandins from polyunsaturated fatty acid (PUFA) precursors provided in yolk lipoprotein complexes. Here we use genetics and electrospray ionization tandem mass spectrometry to partially delineate F-series prostaglandin metabolism pathways. We show that omega-6 and omega-3 PUFAs, including arachidonic and eicosapentaenoic acids, are converted into more than 10 structurally related F-series prostaglandins, which function collectively and largely redundantly to promote sperm guidance. Disruption of omega-3 PUFA synthesis triggers compensatory up-regulation of prostaglandins derived from omega-6 PUFAs. C. elegans F-series prostaglandin synthesis involves biochemical mechanisms distinct from those in mammalian cyclooxygenase-dependent pathways, yet PGF2α stereoisomers are still synthesized. A comparison of F-series prostaglandins in C. elegans and mouse tissues reveals shared features. Finally, we show that a conserved cytochrome P450 enzyme, whose human homolog is implicated in Bietti's Crystalline Dystrophy, negatively regulates prostaglandin synthesis. These results support the model that multiple cyclooxygenase-independent prostaglandins function together to promote sperm motility important for fertilization. This cyclooxygenase-independent pathway for F-series synthesis may be conserved.

Mobilization of ectopic yolk in Gallus domesticus: a novel reverse lipid transport process

In many oviparous animals, bursting type atresia of ovarian follicles occurs during the reproductive cycle, resulting in the escape of yolk into the extracellular compartment. In birds, this ectopic yolk is rapidly cleared by an unknown process that involves the appearance of yolk-engorged macrophage-like cells. To study this unique type of lipid transport, we injected young male chickens intra-abdominally with egg yolk. Absorption of egg yolk from the body cavity markedly increased the triacylglyceride-rich fraction (TRL) of plasma lipoproteins and was coincident with increased levels of plasma triacylglycerides (TAGs) but not non-esterified fatty acids (NEFAs). Thus, the transport of yolk lipids from the abdominal cavity appears to occur in lipoproteins and be more similar to the transport of hepatic TAGs to the periphery via lipoproteins than to transport of adipose TAGs to the periphery via NEFAs released by the action of lipases. When macrophages were exposed to yolk in vitro, they quickly phagocytized yolk; however, it is unclear whether this level of phagocytosis contributes significantly to total yolk clearance. Instead, the chicken macrophage may function more as a facilitator of yolk clearance through the modification of yolk lipoproteins and the regulation of the local and systemic immune response to ectopic yolk. Yolk appears to be anti-inflammatory in nature. Yolk did not increase levels of the inflammatory cytokines IL-1, IL-6 and IFNγ either in vivo or in vitro; in fact, yolk dampened many inflammatory changes caused by lipopolysaccharide (LPS). Conversely, LPS-induced inflammation retarded yolk clearance from the abdominal cavity and plasma TAG levels.

Complex coacervates obtained from interaction egg yolk lipoprotein and polysaccharides

Protein–polysaccharide coacervates formation was evaluated under influence of pH (3.0, 4.0, 6.5, 8.5 and 10.0), temperature (10, 20, 30, 40 and 50 °C) and polysaccharide mass (0.025, 0.033 and 0.050 g). It was possible to observe that solutions with lower turbidity values were found in pH band 3.0 to 4.0. Statistical analysis of turbidity data have shown that for all polymers pH was meaningful in coacervate formation, although for some, besides pH, temperature and polymer concentration could also influence significantly (p < 0,05) in coacervate formation. Encapsulates morphology made by coacervation was directly linked to the kind of polymer used and its interactional degree. Dehydrated coacervates have presented heterogeneous morphology, different from their original structures.

Cloning and expression profiling of the VLDLR gene associated with egg performance in duck (Anas platyrhynchos)

BackgroundThe very low density lipoprotein receptor gene (VLDLR), a member of the low density lipoprotein receptor (LDLR) gene family, plays a crucial role in the synthesis of yolk protein precursors in oviparous species. Differential splicing of this gene has been reported in human, rabbit and rat. In chicken, studies showed that the VLDLR protein on the oocyte surface mediates the uptake of yolk protein precursors into growing oocytes. However, information on the VLDLR gene in duck is still scarce.MethodsFull-length duck VLDLR cDNA was obtained by comparative cloning and rapid amplification of cDNA ends (RACE). Tissue expression patterns were analysed by semi-quantitative reverse-transcription polymerase chain reaction (RT-PCR). Association between the different genotypes and egg performance traits was investigated with the general linear model (GLM) procedure of the SAS® software package.ResultsIn duck, two VLDLR transcripts were identified, one transcript (variant-a) containing an O-linked sugar domain and the other (variant-b) not containing this sugar domain. These transcripts share ~70 to 90% identity with their counterparts in other species. A phylogenetic tree based on amino acid sequences showed that duck VLDLR proteins were closely related with those of chicken and zebra finch. The two duck VLDLR transcripts are differentially expressed i.e. VLDLR-a is mainly expressed in muscle tissue and VLDLR-b in reproductive organs. We have localized the duck VLDLR gene on chromosome Z. An association analysis using two completely linked SNP sites (T/C at position 2025 bp of the ORF and G/A in intron 13) and records from two generations demonstrated that the duck VLDLR gene was significantly associated with egg production (P < 0.01), age of first egg (P < 0.01) and body weight of first egg (P < 0.05).ConclusionsDuck and chicken VLDLR genes probably perform similar function in the development of growing oocytes and deposition of yolk lipoprotein. Therefore, VLDLR could be a candidate gene for duck egg performance and be used as a genetic marker to improve egg performance in ducks.

Insulin/FOXO Signaling Regulates Ovarian Prostaglandins Critical for Reproduction

Abnormalities in insulin/IGF-1 signaling are associated with infertility, but the molecular mechanisms are not well understood. Here we use liquid chromatography with electrospray ionization tandem mass spectrometry to show that the C. elegans insulin/FOXO pathway regulates the metabolism of locally acting lipid hormones called prostaglandins. C. elegans prostaglandins are synthesized without prostaglandin G/H synthase homologs, the targets of nonsteroidal anti-inflammatory drugs. Our results support the model that insulin signaling promotes the conversion of oocyte polyunsaturated fatty acids (PUFAs) into F-series prostaglandins that guide sperm to the fertilization site. Reduction in insulin signaling activates DAF-16/FOXO, which represses the transcription of germline and intestinal genes required to deliver PUFAs to oocytes in lipoprotein complexes. Nutritional and neuroendocrine cues target this mechanism to control prostaglandin metabolism and reproductive output. Prostaglandins may be conserved sperm guidance factors and widespread downstream effectors of insulin actions that influence both reproductive and nonreproductive processes.

Interactions of egg yolk lipoprotein fraction with boar spermatozoa assessed with a fluorescent membrane probe.

The interactions of a fluorescent membrane probe, 1-anilinonaphthalene-8-sulfonic acid (1,8-ANS), with boar spermatozoa were followed through the use of lipoprotein fraction of ostrich egg yolk (LPFo). Semen samples, extended in Kortowo 3 (K3) extender, were supplemented with 2% or 5% LPFo and stored for 3h at 16 degrees C. Additionally, cold shock-treated spermatozoa (1h at 4 degrees C) were stored in K3 extender supplemented with LPFo for 3h at 16 degrees C. In each boar, the fluorescent enhancement of ANS was observed in K3-extended semen supplemented with LPFo, prior to storage. Following storage, there was a significant increase in LPFo-ANS fluorescence, particularly in the sperm membrane overlying the head and midpiece regions. There were significant differences among the boars with respect to the sperm populations defined by the LPFo-ANS fluorescence. Sperm viability was not significantly affected during the storage period. Furthermore, the proportions of spermatozoa defined by the different patterns of LPFo-ANS fluorescence were low and remained unchanged after storage of cold shock-treated spermatozoa with 2% or 5% LPFo, suggesting irreversible damage to the sperm membrane architecture. These findings indicate that the ANS fluorescent probe could be used to shed more light on the nature of the interactions between LPFo and sperm membrane following semen preservation. Such valuable information could contribute to the development of an optimal protocol for cryopreservation of boar semen.

Interactions of egg yolk lipoprotein fraction with boar spermatozoa assessed with a fluorescent membrane probe.

Interactions of egg yolk lipoprotein fraction with boar spermatozoa assessed with a fluorescent membrane probe.

Effect of different storage temperatures on the metabolic activity of spermatozoa following liquid storage of boar semen

This study investigated the effects of different temperatures (5o and 16oC) on the metabolic activity of boar spermatozoa preserved in a standard semen extender, Kortowo 3 (K3), supplemented with or without egg yolk lipoprotein fractions (LPF) isolated from hen or ostrich egg yolk. Besides motility and plasma membrane integrity (PMI) assessments of spermatozoa, analysis of the metabolic activity of spermatozoa included mitochondrial energy status, oxygen uptake, ATP content and L-lactate production. Total motility and PMI of spermatozoa decreased over time. The metabolic activity of spermatozoa was significantly higher in the extenders containing LPF than in the K3 extender. Marked changes in the sperm metabolic activity observed during storage of semen samples at 5oC indicated that glycolysis (fructolysis) was the major metabolic pathway. It seemed likely that mitochondrial respiration was the predominant metabolic activity exhibited by spermatozoa during storage at 16oC. The findings of this study indicate that different storage temperatures can modulate the metabolic pathways of boar spermatozoa during liquid semen storage.

Efecto del antiveneno botrópico sobre las actividades de fosfolipasa a2, l-aminoácido oxidasa y hialuronidasa de los venenos de serpientes peruanas

Bothrops sp. snakes causing the largest number of cases of ophidism in Peru, their venom contain several enzymes related to poison spreading, miotoxic and platelet aggregation disturbances. Objectives. The inhibiting capacity of liquid polivalent bothropic antivenom from Instituto Nacional de Salud (INS) has been evaluated on phospholipase A 2 (PLA2), L amino acid oxidase (LAO) and hyaluronidase activities using B. atrox, B. barnetti, B. brazili and B. pictus venoms. Material and methods. In each case on 45% egg yolk lipoprotein, Lleucina and O-dianisidine, as well as hyaluronic acid as substrates respectively, using for each enzyme ½, 1 and 2 doses of either natural and heated (37 °C during five days) antivenom, assayed in triplicate. Results. HA was more neutralized enzyme for antivenin, all venoms with the exception of B. brazili were totally inhibited at any dose. For LAO had values of inhibition of 68 to 100% using two doses of the antivenin, PLA2 was the least inhibited (70 to 80%) to two doses. With the heated antivenin was a decline of the inhibitory effect initially found. Conclusions. The measurement of the HA might serve as an indicator of the in vitro potency of antivenins, the bothropic antivenin produced by INS keeping in vitro conditions for inhibition of three major activities of the Peruvian snake venoms.

Molecular dynamics simulations of a lipovitellin-derived amphiphilic β-sheet homologous to apoB-100 β-sheets at a hydrophobic decane–water interface

Lipovitellin, an egg-yolk lipoprotein, transports lipids in a pocket surrounded by amphiphilic β-sheets. Its X-ray structure provides possibilities to study interactions between lipophilic β-sheets and lipids at the atomic level. Here, we studied a 67-residue-long amphiphilic β-sheet of lipovitellin previously suggested a suitable working model for studies of the lipid-binding behaviour of amphiphilic β-sheet regions in apolipoprotein B-100 (apoB-100). We performed four molecular dynamics simulations with different starting configurations to define characteristics of the amphiphilic β-sheet model at a decane–water interface. In each simulation the model β-sheet bound keenly to the decane layer via its hydrophobic surface. The structural profiles showed unchanged secondary structure of the β-sheet during the attachment. Also, aromatic side chains, especially tryptophans and tyrosines, mediated the attachment to the hydrophobic layer and influenced the orientation of the decane molecules that are in contact with the β-sheet. In conclusion, the present simulations reveal high affinity of a lipovitellin-derived amphiphilic β-sheet to a hydrophobic decane layer. They lay thereby the basis for further studies of the interaction between amphiphilic β-sheets and lipids in complex molecular systems, like LDL particles, in which the large apoB-100 is the main protein component.

Cholesterol-Lowering Activity of Plant Sterol-Egg Yolk Lipoprotein Complex in Rats

Free plant sterols cannot be dissolved in oil or water. Using free plant sterols and egg yolks, we developed a plant sterol-egg yolk lipoprotein complex (PSY) that can be dispersed in water and considered suitable for use in processed foods. The cholesterol-lowering activity of PSY was equal to that of free plant sterols and plant sterol esters. Consumption of a freeze-dried PSY-containing omelet reduced serum and hepatic cholesterol concentrations. The results suggest that PSY has cholesterol-lowering activity equivalent to that of free plant sterols and plant sterol esters. Moreover, the cholesterol-lowering activity of PSY was maintained in processed foods.

Is there a relationship between the chromatin status and DNA fragmentation of boar spermatozoa following freezing–thawing?

In this study a radioisotope method, which is based on the quantitative measurements of tritiated-labeled actinomycin D ( 3H-AMD) incorporation into the sperm nuclei ( 3H-AMD incorporation assay), was used to assess the chromatin status of frozen–thawed boar spermatozoa. This study also tested the hypothesis that frozen–thawed spermatozoa with altered chromatin were susceptible to DNA fragmentation measured with the neutral comet assay (NCA). Boar semen was diluted in lactose-hen egg yolk-glycerol extender (L-HEY) or lactose ostrich egg yolk lipoprotein fractions-glycerol extender (L-LPFo), packaged into aluminum tubes or plastic straws and frozen in a controlled programmable freezer. In Experiment 1, the chromatin status and DNA fragmentation were measured in fresh and frozen–thawed spermatozoa from the same ejaculates. There was a significant increase in sperm chromatin destabilization and DNA fragmentation in frozen–thawed semen as compared with fresh semen. The proportions of spermatozoa labeled with 3H-AMD were concurrent with elevated levels of sperm DNA fragmentation in K-3 extender, without cryoprotective substances, compared with L-HEY or L-LPFo extender. Regression analysis revealed that the results of the 3H-AMD incorporation assay and NCA for frozen–thawed spermatozoa were correlated. Boars differed significantly in terms of post-thaw sperm DNA damage. In Experiment 2, the susceptibility of sperm chromatin to decondensation was assessed using a low concentration of heparin. Treatment of frozen–thawed spermatozoa with heparin revealed enhanced 3H-AMD binding, suggesting nuclear chromatin decondensation. The deterioration in post-thaw sperm viability, such as motility, mitochondrial function and plasma membrane integrity, was concurrent with increased chromatin instability and DNA fragmentation. This is the first report to show that freezing–thawing procedure facilitated destabilization in the chromatin structure of boar spermatozoa, resulting in an unstable DNA that was highly susceptible to fragmentation.

Depletion flocculation effects in egg-based model salad dressing emulsions

The influence of dehydrated egg white (DEW) addition on the droplet aggregation of yolk-based model salad dressing emulsions was studied in an attempt to investigate the role of the egg albumen fraction in the physicochemical changes that take place during the storage of acidic emulsions containing whole egg. Analysis of the adsorbed protein in emulsion by the application of SDS–PAGE provided strong evidence for the almost complete exclusion of the egg albumen from the droplet surfaces by the more flexible yolk lipoproteins. The results on emulsion stability are discussed in terms of possible depletion effects that may arise from the presence of the non-adsorbed egg white proteins in the continuous phase. Observations of emulsions under the light microscope and rheological measurements are presented to support the hypothesis that the extensive droplet–droplet aggregation effects, arising from the presence of unadsorbed albumen proteins, result in emulsion destabilization against creaming.