Interactions between pig gastric mucin and sodium caseinate in solutions and in emulsions

The interactions between pig gastric mucin (PGM) and sodium caseinate (Cas) were studied in solutions and in Cas-stabilized emulsions with respect to the ratio of the two components and the pH (1-7) with an emphasis on pH cycling, using absorbance, zeta potential, light scattering, creaming and microscopy measurements. In solutions, pH-reversible interactions were observed at pH 3 or lower, down to pH 1. Zeta potential measurements suggest that interactions are electrostatic in nature at pH 3, while the negligible charge of PGM allows for some attractive interactions with positively charged Cas at pH 1. Caseinate-stabilized oil-in-water emulsions are stable toward coalescence at pH 1 and pH 7; some coalescence is observed at pH 3. Addition of PGM results in flocculation, either due to depletion (pH 7), or due to bridging flocculation and Cas-PGM interactions similar to those observed in solution (pH 1 and pH 3). The flocculation is reversible, as is shown in pH cycling at pH 1 to pH 7, then to pH 1. Overall, the above can be of interest as an examination of the fate of emulsions in pH transitions and cycling in the human gastrointestinal tract. (C) 2012 Elsevier Ltd. All rights reserved.