Elisabeth David-Briand

Lipolysis in muscles during refrigerated storage as related to the metabolic type of the fibres in the rabbit.

The relation between lipolysis and the metabolic fibre type was investigated during refrigerated storage of rabbit muscles. Free fatty acid, monoacylglycerol and diacylglycerol contents and free fatty acid composition were compared in five muscles immediately after slaughter and after a 7-day-storage at 4°C. The results showed that. (1) The amount of free fatty acids sharply increased during the refrigerated storage (from 2-10 to 11-32 mg/100 g of muscle), especially that of long chain polyunsaturated fatty acids (from less than 0.1 to 1.4-3.3 mg/100 g of muscle). (2) The glycolytic muscles contained 1.5 times less free fatty acids than the oxidative ones. However, the rates of phospholipid and triacylglycerol hydrolysis were not related to the metabolic type of the fibres. (3) The contribution of phospholipids to free fatty acid fraction was twice that of triacylglycerols in the glycolytic muscles whereas it was similar or lower to that of triacylglycerols in the oxidative muscles.

Egg yolk phosvitin: preparation of metal-free purified protein by fast protein liquid chromatography using aqueous solvents

Two chromatographic methods for hen egg yolk phosvitin purification avoiding organic solvents were evaluated. Hydrophobic interaction and ion-exchange chromatographies were applied to isolated phosvitin. Hydrophobic interaction chromatography has better capacity than ion-exchange chromatography to fractionate phosvitin in their different polypeptides, but its protein yield was lower (0.7 vs. 1.7% of egg yolk dry matter). Finally, ion-exchange chromatography was selected and allowed to fractionate phosvitin polypeptides, including the recovering of phosphoproteins with high electrophoretic mobility: phosvettes. Highly purified (>98%) and free metal protein was obtained in reduced time. Phosvitin polypeptide heterogeneity was evidenced.

Interfacial and oil/water emulsions characterization of potato protein isolates.

Interfacial and emulsifying properties of potato protein isolate (PPI) have been studied to evaluate its potential application to stabilize oil/water emulsions at two pH values (2 and 8). The amount, type, and solubility of proteins and the size of aggregates have been determined in aqueous dispersion. Air-water and oil-water interfacial properties (adsorption, spreading, and viscoelastic properties) have been determined as a function of concentration and pH using soluble phases of PPI. The behavior of PPI stabilized oil/water emulsions has been then analyzed by droplet size distribution measurements and interfacial concentration. PPI exhibits low solubility over a wide range of pH values, with the presence of submicrometer aggregates. The pH value exerts a negligible effect on interfacial tension (oil-water) or surface pressure (air-water) but displays very important differences in viscoelastic properties of the interfacial films formed between oil and water. In this sense, pH 8 provides a major elastic response at oil-water interfaces as compared to pH 2. In relation with this result, a much higher ability to produce fine and stable emulsions is noticed at pH 8 as compared to pH 2. Consequently, there is an evident relationship between the rheological properties of the oil-water interfacial films and the macroscopic emulsion behavior.

Influence of Ionic Complexation on Release Rate Profiles from Multiple Water-in-Oil-in-Water (W/O/W) Emulsions

Water-in-oil-in-water (W/O/W) double emulsions were prepared, and the kinetics of release of magnesium ions from the internal to the external water phase was followed. Different chelating agents (phosvitin and gluconate) were used to bind magnesium within the prospect of improving the ion retention in the internal aqueous droplets. Magnesium release was monitored for 1 month of storage, for each formulation, with and without chelation, at two storage temperatures (4 and 25 degrees C). Leakage occurred without film rupturing (coalescence) and was mainly due to entropically driven diffusion/permeation phenomena. The experimental results revealed a clear correlation between the effectiveness of chelating agents to delay the delivery and their binding capacity characterized by the equilibrium affinity constant. The kinetic data (percent released versus time curves) were interpreted within the framework of a kinetic model based on diffusion and taking into account magnesium chelation.

Organization of lipids in the artificial outer membrane of bull spermatozoa reconstructed at the air–water interface

Cryopreservation is widely used to preserve the quality of bull spermatozoa over time. Sequestration of seminal plasma proteins by low density lipoproteins and formation of a protective film around the spermatozoa membrane by low density lipoproteins were the main mechanisms proposed. However, the organization of lipids in the outer leaflet of the spermatozoa membrane has been never considered as a possible parameter. This study evaluated whether a change in the organization of the outer leaflet of the spermotozoa membrane could occur during cooling down. The organization of the main components of the spermatozoa membranes outer layer at the liquid-gas interface was analysed. Cryopreservative media (at 8° and 34°C) were used to study the miscibility of the spermatozoa membrane lipids using epifluorescence imaging and by tensiometry on Langmuir films. The results show that the four lipids: sphingomyelin, cholesterol, 1-palmitoyl-2-docosahexaenoyl-sn-glycero-3-phosphocholine (PC) and plasmalogen 1-(1Z-octadecenyl)-2-docosahexaenoyl-sn-glycero-3-phosphocholine (P-PC) were not fully miscible and their organization was controlled by temperature. Cholesterol and sphingomyelin form condensed domains surrounded by a mixture of PC and P-PC at 34°C while these condensed domains are surrounded by separated domains of pure PC and pure P-PC at 8°C. The organization of the outer membrane lipids, in particular the separation of PC and P-PC lipids during cooling down, must be considered to fully understand preservation of membrane integrity during cryopreservation.

The phase and charge of milk polar lipid membrane bilayers govern their selective interactions with proteins as demonstrated with casein micelles

The biological membrane surrounding fat globules in milk (milk fat globule membrane; MFGM) is an interface involved in many biological functions and interactions with the surrounding proteins or lipolytic enzymes in the gastro-intestinal tract during digestion. The MFGM exhibits lateral heterogeneities resulting from the different phase states and/or head-group charge of the polar lipids, which were both hypothesized to drive interaction with the casein micelles that is the major milk protein assembly. Atomic force microscopy (AFM) imaging was used to track the interactions of casein micelles with hydrated supported lipid bilayers of different composition, phase state and charge. Zeta-potential and Langmuir isotherms of the different polar lipids offered additional information necessary to interpret AFM observations. We showed that the negatively-charged casein micelles did not interact with milk sphingomyelin in the gel or liquid-ordered phases but did interact with polar lipids in the liquid-disordered phase (unsaturated polar lipids and milk sphingomyelin above its melting point). A wide intermolecular distance between polar lipids allowed protein adsorption on the membranes. However, the presence of the anionic polar lipids phosphatidylserine and phosphatidylinositol prevented any interaction with the casein micelles, probably due to electrostatic repulsion. These results open perspectives for the preparation of tailored emulsions covered by polar lipids able to modulate the interfacial interactions with proteins.