29B-32 |
Role of non-adsorbed protein on droplet flocculation in hexadecane oil-in-water emulsions stabilized by b-lactoglobulin |
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 Most food emulsions contain a certain quantity of non-adsorbed proteins (free protein) in the aqueous phase. These proteins are known to influence emulsion stability, but there is currently a poor understanding of the physicochemical origin of this effect. Our goal is to understand the role of free protein on droplet flocculation in oil-in-water emulsions. n-Hexadecane oil-in-water emulsions (pH 7.0, 20 wt%) stabilized by b-lactoglobulin (0.8 wt% b-Lg) were prepared (free protein < 0.05 wt%). Isothermal stability studies were carried out by adding NaCl (0-150 mM) and free protein (0 to 0.6 wt %) to emulsions immediately after homogenization, and measuring the increase in mean particle diameter (d) using laser diffraction with time at 30 oC. Thermal stability studies were carried out by adding NaCl (0 or 150 mM) and free protein (0 or 0.4 wt%) to the emulsions and measuring d after heat treatments (30-95 oC for 20 min). In the isothermal stability studies, we observed a rapid increase in d when salt was added to emulsions containing no free protein, but a much slower increase when salt was added with free protein. The added protein likely adsorbed to the droplet surfaces and reduced their surface hydrophobicity, thereby reducing droplet attraction. In the thermal stability studies, we observed extensive droplet flocculation at all temperatures when NaCl was added to emulsions containing no free protein, but little droplet flocculation at any temperature when NaCl was added in the presence of free protein. It seems that when free proteins are in close proximity during heating, interactions between adsorbed and free proteins are favored, but when free proteins are not in close proximity, interactions between proteins adsorbed onto different droplets are favored. This study has important implications for the formulation and production of protein stabilized oil-in-water emulsions with improved stability.
Session 29B, Food Chemistry: Lipids, antioxidants and emulsifiers
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