29B-24 |
Influence of sodium dodecyl sulfate on the droplet flocculation of b-lactoglobulin stabilized oil-in-water emulsions |
J. Yokota, H. J. KIM, E. A. Decker, and D. J. McClements. Dept. of Food Science, Univ. of Massachusetts, Amherst, Chenoweth Lab., Box 31410, Amherst, MA 01003-1410 Ionic surfactants can be used to improve the thermal stability of protein stabilized oil-in-water emulsions. Various mechanisms may contribute to this effect, including (i) changing the thermal denaturation temperature of adsorbed b-lactoglobulin; (ii) altering the strength of droplet-droplet interactions by modifying droplet charge; (iii) displacing proteins. Our goal was to identify the physicochemical mechanism(s) by which a model anionic surfactant (sodium dodecyl sulfate, SDS) improved the thermal stability of a globular protein-stabilized emulsion. n-Hexadecane oil-in-water emulsions (pH 7.0, 20 wt%) stabilized by b-lactoglobulin (0.8 wt% b-Lg) were prepared using a high-pressure valve homogenizer. NaCl (150 mM) and SDS with various surfactant-to-protein molar ratios (R, 0 < R< 40) were added to the emulsions either before or after heating at 90 oC for 20 min. To examine the influence of SDS on the thermal stability of emulsions, SDS (R=10) and NaCl solution were added to the emulsion either before or after heat treatment (30-95 oC for 20 min). The degree of droplet flocculation in the emulsions was measured by laser light scattering. The electrical charge was measured by z-potential measurements. The protein concentration in the serum phase was determined by measuring the absorbance at 280 nm after repeated centrifugation and filtration. At R > 20, SDS replaced adsorbed protein at the interface and stabilized droplet flocculation against heat treatment. At R=10, SDS added before heating bound to the interfacial protein and greatly reduced droplet flocculation during heating, probably due to a reduced hydrophobic attraction and an increased electrostatic repulsion between the droplets. When SDS (R=10) was added after heating, it could not disrupt flocs that had been formed at the higher temperatures (> 65 oC). These results may have important applications in the development of emulsions with improve stability to thermal processing
Session 29B, Food Chemistry: Lipids, antioxidants and emulsifiers
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