29B-34 |
The impact of heat and salt on the droplet flocculation in corn oil-in-water emulsion stabilized by WPI at pH 3 |
D. DJORDJEVIC1, H. J. Kim2, D. J. McClements1, and E. A. Decker1. (1) Dept. of Food Science, Univ. of Massachusetts, Amherst, Chenoweth Lab., Box 31410, Amherst, MA 01003-1410, (2) MA Whey proteins are functional ingredients of many foods, including emulsions. A major application of whey protein is an emulsifying agent. Ionic strength, heating and pH conditions common to foods can influence whey protein structure and therefore emulsion stability. The influence of oil concentration, heating, and salt addition on the droplet flocculation and rheology of corn oil-in-water emulsions stabilized by whey protein isolate (WPI) was studied. Different concentrations (5-50 wt %) of corn oil-in-water emulsions (pH 3) stabilized by WPI (0.5-5 wt %) were prepared by high-pressure valve homogenization. Salt (0 or 150 mM NaCl) was added to corn oil-in-water emulsions either before or after isothermal heat treatment (30-90°C for 30 min). Particle size distribution was measured by laser diffraction. Apparent viscosity and oscillation (shear modulus) were measured using a dynamic shear rheometer. The apparent viscosity of the emulsions increased with oil concentrations ³ 35 % wt oil, however particle size distribution was not effected. Addition of NaCl to the 30 wt % corn oil-in-water emulsion increased particle size distribution (0.4-0.5 µ m) compared to the emulsion without salt (0.25-0.35 µ m). At 0 mM NaCl, no droplet aggregation was observed in any of the heated emulsion. Addition of 150 mM NaCl to emulsions before or after heating increased particle size diameter (0.5-0.8 µ m) at heating temperatures 30-65°C. At temperatures above 65°C, increases in particle size distribution became less extensive when salt was added to the emulsion after heating, but more extensive when the salt was added before heating. Oscillation results indicated that gel formation in emulsions depended on the salt addition (150 mM NaCl) and heating (75°C for 30 min) with salt and heat-treated emulsion having the highest complex modulus. This study has important implications for the formation and stability of protein stabilized oil-in-water emulsions.
Session 29B, Food Chemistry: Lipids, antioxidants and emulsifiers
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