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 11,252 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We report on shear rheological measurements at 30&deg;C of fine oil-in-water emulsions (volume-surface average diameter < 0.5 &mgr;m) prepared at pH 6.8 with sodium caseinate as the sole emulsifier (1-6 wt%) and n -tetradecane as the dispersed phase (10, 35, or 45 vol%). Strong sensitivity of rheological behavior to total protein concentration was indicated by both steady-state viscometry and small-deformation oscillatory experiments. The behavior can be classified into three types, depending on the protein/oil ratio. (1) Emulsions containing insufficient protein for (near-) saturation protein surface coverage develop a time-dependent increase in low-stress apparent viscosity and associated shear-thinning behavior; this can be attributed to bridging flocculation. (2) Emulsions having full protein surface coverage but relatively little excess unadsorbed protein in the continuous phase are stable Newtonian liquids. (3) Emulsions containing a substantial excess of unadsorbed sodium caseinate exhibit considerable pseudoplasticity which can be attributed to depletion flocculation. Taken as a whole, the time-dependent rheological properties for this set of emulsions as a function of protein content and oil volume fraction are largely consistent with our previous results on the creaming stability and the particle gel microstructure for these same emulsion systems. In particular, the reversible flocculation of emulsion samples of high protein content is readily explicable in terms of depletion flocculation of droplets by unadsorbed protein existing in the form of approximately spherical caseinate submicelles.
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PMID:Rheology of Sodium Caseinate Stabilized Oil-in-Water Emulsions 924 Dec 17

The creaming and rheology of fine n-tetradecane oil-in-water emulsions at pH 6.8 containing the commercial protein sodium caseinate and the ionic surfactant sodium dodecyl sulfate (SDS) have been studied, and an overview diagram relating surfactant composition and creaming stability has been constructed. The presence of both SDS and sodium caseinate in an emulsion system increases the overall stability with respect to creaming. Excess SDS promotes destabilization through fast creaming; this can be attributed to depletion flocculation brought about by unadsorbed surfactant micelles. Addition of sodium caseinate was found to reduce this effect, even at relatively high SDS concentrations. The behavior of the caseinate + SDS emulsions is thus different from the behavior of the previously reported caseinate + Tween 20 systems, where the combination of the two surface-active agents was found to reduce the emulsion stability, as indicated by fast creaming and shear-thinning rheology. Addition of sodium chloride was found to increase the extent of non-Newtonian behavior and to enhance the degree of creaming for SDS-containing emulsions. Increased caseinate levels in these systems seem to offer some stabilization through reduction of the shear-thinning character and improvement in creaming stability. These phenomena can be explained in terms of a considerable amount of SDS binding to the protein, which reduces the amount of SDS available to promote protein displacement and depletion flocculation. In contrast to the SDS systems, the properties of equivalent emulsions containing caseinate + nonionic surfactant Tween 20 are relatively insensitive to salt content. Copyright 2000 Academic Press.
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PMID:Creaming and Rheology of Oil-in-Water Emulsions Containing Sodium Dodecyl Sulfate and Sodium Caseinate. 1070 4

The formation, stability, and rheological behavior of a hexagonal phase based gel-emulsion (O/H1 gel-emulsion) have been studied in water/C12EO8/hydrocarbon oil systems. A partial phase behavior study indicates that the oil nature has no effect on the phase sequences in the ternary phase diagram of water/C12EO8/oil systems but the domain size of the phases or the oil solubilization capacity considerably changes with oil nature. Excess oil is in equilibrium with the hexagonal phase (H1) in the ternary phase diagram in the H1+O region. The O/H1 gel-emulsion was prepared (formation) and kept at 25 degrees C to check stability. It has been found that the formation and stability of the O/H1 gel-emulsion depends on the oil nature. After 2 min observation (formation), the results show that short chain linear hydrocarbon oils (heptane, octane) are more apt to form a O/H1 gel-emulsion compared to long chain linear hydrocarbon oils (tetradecane, hexadecane), though the stability is not good enough in either system, that is, oil separates within 24 h. Nevertheless, the formation and stability of the O/H1 gel-emulsion is appreciably increased in squalane and liquid paraffin. It is surmised that the high transition temperature of the H1+O phase and the presence of a bicontinuous cubic phase (V1) might hamper the formation of a gel-emulsion. It has been pointed out that the solubilization of oil in the H1 phase could be related to emulsion stability. On the other hand, the oil nature has little or no effect on the formation and stability of a cubic phase based gel-emulsion (O/I1 gel-emulsion). From rheological measurements, it has found that the rheogram of the O/H1 gel-emulsion indicates gel-type structure and shows shear thinning behavior similar to the case of the O/I1 gel-emulsion. Rheological data infer that the O/I1 gel-emulsion is more viscous than the O/H1 gel-emulsion at room temperature but the O/H1 gel-emulsion shows consistency at elevated temperature.
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PMID:Hexagonal phase based gel-emulsion (O/H1 gel-emulsion): formation and rheology. 1884 93

Oil-in-water emulsions (10% w/w n-tetradecane) were prepared at pH = 5.7 by using, as surface active agents, electrostatically formed complexes of sodium stearoyl lactylate (SSL) at a concentration of 0.4% (w/w) and chitosan (CH) in a concentration range between 0 and 0.48% w/w. The use of complexes in emulsions with a low concentration of CH (<0.24% w/w) resulted in highly flocculated systems; instead, with increased level of CH, the emulsions had a smaller average droplet size and exhibited greater stability during storage. Emulsions stabilised by SSL/CH complexes showed non-Newtonian flow behavior with pronounced shear thinning. Among all formulations studied none showed a gel-like behavior since in all cases the G' (storage modulus) was lower that G'' (loss modulus). Adsorption kinetics of pure SSL and SSL/CH complexes to the oil/water interfaces were evaluated using an automated drop tensiometer (ADT). Even though complexation of SSL with CH resulted in a delay of the adsorption of the surface active species at the oil/water interface, the inclusion of the polysaccharide resulted in substantially improved interfacial properties as indicated by a significant increase of the dilatational modulus. Furthermore, the enhanced interfacial properties of the emulsion droplets resulted in improved stability against freeze-thaw cycling. The results of this study may facilitate the development of frozen food products such as desserts with an ameliorated stability and favorable sensorial characteristics.
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PMID:Engineering interfacial properties by anionic surfactant-chitosan complexes to improve stability of oil-in-water emulsions. 2229 29