| Abstract
| - The influence of thermal processing on droplet flocculation in oil-in-water emulsions stabilized by eitherβ-lactoglobulin (primary emulsions) or β-lactoglobulin−ι-carrageenan (secondary emulsions) at pH 6 hasbeen investigated. In the absence of salt, the ζ-potential of the primary emulsion was less negative (−40mV) than that of the secondary emulsion (−55 mV) due to adsorption of anionic ι-carrageenan to theanionic β-Lg-coated droplet surfaces. The ζ-potential and mean diameter (d43 ≈ 0.3 μm) of droplets inprimary and secondary emulsions did not change after storage at temperatures ranging from 30 to 90 °C.In the presence of 150 mM NaCl, the ζ-potential of the primary emulsion was much less negative (−27mV) than that of the secondary emulsion (−50 mV), suggesting that the latter was less influenced byelectrostatic screening effects. The ζ-potential of the primary emulsions did not change after storage atelevated temperatures (30−90 °C). The ζ-potential of the secondary emulsions became less negative, andthe aqueous phase ι-carrageenan concentration increased at storage temperatures exceeding 50 °C, indicatingι-carrageenan desorbed from the β-Lg-coated droplets. In the primary emulsions, appreciable dropletflocculation (d43 ≈ 8 μm) occurred at temperatures below the thermal denaturation temperature (Tm) ofthe adsorbed proteins due to surface denaturation, while more extensive flocculation (d43> 20 μm) occurredabove Tm due to thermal denaturation. In the secondary emulsions, the extent of droplet flocculation belowTm was reduced substantially (d43 ≈ 0.8 μm), which was attributed to the ability of adsorbed carrageenanto increase droplet−droplet repulsion. However, extensive droplet flocculation was observed above Tmbecause carrageenan desorbed from the droplet surfaces. Differential scanning calorimetry showed thatι-carrageenan and β-Lg interacted strongly in aqueous solutions containing 0 mM NaCl, but not in thosecontaining 150 mM NaCl, presumably because salt weakened the electrostatic attraction between themolecules.
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