Saliva-Induced Emulsion Flocculation: Role of Droplet Charge - Food Colloids: Self-Assembly and Material Science - page 471

Figure 4 Saliva (0.6 mg mL 1 ) before mixing (left cuvette) and after mixing (right
cuvette) with protein (5 mg mL 1 lysozyme solution) at pH ¼ 7. On the
extreme right is a CSLM image (79 79 m m) showing complex formation
between saliva and OG-lysozyme
mechanism of emulsion + saliva mixtures. Different scenarios have been
shown to occur depending upon the measured z -potential of the droplets. No
flocculation was found for highly negatively charged emulsions, which is
ascribed to electrostatic repulsion preventing close approach of the droplets.
Reversible flocculation was found for weakly negatively charged and neutral
emulsion droplets, probably induced by salivary mucins via depletion interac-
tions. Instead, for positively charged emulsion droplets, we propose a bridging
mechanism induced by electrostatic attraction between salivary proteins and
the surface of the droplets. Furthermore, we have demonstrated that saliva can
form complexes in solution with a positively charged polymer such as lysozyme,
and this is likely to occur in the continuous phase of emulsions as well. It
reinforces the idea that the electrostatic interaction between salivary compo-
nents - for example, the negatively charged mucins - and positively charged
emulsifiers, both in the adsorbed state and in the continuous phase, can have an
influence on emulsion behaviour in the oral cavity.
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