Composition of fat protein layer in complex food emulsions at various weight ratios of casein-to-whey proteins

Abstract

-We studied three complex food emulsions which differed only by the weight ratio of casein-to-whey proteins (80:20, 60:40, 0:100). We considered the stability of the fat droplets against aggregation/coalescence, the amount of adsorbed proteins, and the protein composition of the interface. Our results indicated that coalescence was inhibited whatever the protein composition. However, aggregation between fat droplets was observed in the casein-free emulsion (0:100), where the amount of adsorbed proteins at the fat globule surface was the lowest. Quantitative SDS-PAGE experiments showed that preferential adsorption of caseins over globular proteins occurs only in the emulsion based on the intermediate (60:40) casein-to-whey protein ratio. Furthermore, the proportion of adsorbed proteins which were found in polymeric forms seemed to increase with decreasing casein-to-whey protein ratio. The fat globule stability, total fat protein load and proportion of adsorbed protein in the polymeric forms were discussed in terms of adsorption properties of milk proteins at the oil-water interface, in relation to the casein-to-whey protein ratio.Milk protein / emulsion / stability / protein adsorption / disulfide bond Résumé -Composition de la couche protéique adsorbée à la surface des globules gras dans des émulsions alimentaires complexes contenant différents rapports caséine/protéines sériques. Nous avons étudié trois émulsions alimentaires complexes qui ne diffèrent entre elles que par le rapport massique caséine/protéines sériques (80:20 ; 60:40 et 0:100). Cette étude a été réalisée en considérant la stabilité des gouttelettes lipidiques vis-à-vis de l'agrégation/coalescence, la quantité de protéines adsorbées par unité de surface de globule gras et la composition de l'interface. Nos résultats ont montré l'absence de coalescence dans les trois émulsions, et la présence d'agrégats n'a été observée que dans l'émulsion (0:100) ne contenant pas de caséine. Dans ce dernier cas, la quantité de protéines adsorbées à la surface des globules gras est la plus faible. Une étude quantitative par électro-phorèse sur gel de polyacrylamide a indiqué une adsorption préférentielle des caséines par rapport aux protéines sériques dans le cas de l'émulsion préparée à base du ratio intermédiaire (60:40) de caséine/protéines sériques. De plus, la proportion de polymères adsorbés à la surface de globules gras semble augmenter lorsque le rapport massique caséine/protéiques sériques diminue. La stabilité des émulsions, la charge protéique des globules gras et la proportion de polymères adsorbés sont discutées en fonction du rapport caséine/protéines sériques.Protéine laitière / émulsion / stabilité / adsorption des protéines / pont disulfure

Factors governing partial coalescence in oil-in-water emulsions

“…For hydrogenated palm kernel oil (9%) emulsions stabilised by a mixture of caseins and WP, Sourdet et al [55] and Relkin et al [53,56] concluded the preferential adsorption of casein micelles over WP and thereby a higher surface load and stability against partial coalescence of the casein containing emulsions over the 100% whey stabilised emulsions. Next to the effect on the membrane composition, also differences in crystallisation behaviour between the casein containing and the 100% whey stabilised emulsions, were observed by Relkin et al [53,56].…”

Aeration of low fat dairy emulsions: Effects of saturated–unsaturated triglycerides

“…Before sampling, the emulsions were gently stirred at 20 1C, and diluted $1:1000 with either distilled water or a 1% SDS solution to dissociate non-covalently bound fat droplet aggregates (Sourdet, Relkin, Fosseux, & Aubry, 2002). The presentation factor was selected after measuring the refractive index (ABBE Atago 3T, Kent, UK) of dispersed fat relative to water (1.08) and absorbance (0.1) at 633 nm (Varian Cary 100, spectrophotometer, Les Ulis, France).…”

Structural properties of stirred yoghurt as influenced by whey proteins

“…Moreover, the influence of casein to whey protein ratio on the fat globule membrane was examined (Sourdet, Relkin, Fosseux, & Aubry, 2002). In the absence of casein, emulsions tend to aggregation and decreasing fat integration.…”