Improved approach for characterizing the coalescence stability of legumin stabilized O/W emulsions by analytical ultracentrifugation

Abstract

The coalescence stability of n-decane-in-water emulsions stabilized by native and highly (>90%) acetylated legumin, the 11 S main storage protein from faba beans (Vicia faba L.) has been investigated by analytical ultracentrifugation. The method is based on centrifugation at constant rotor speeds (sufficiently high to produce a detectable amount of separated oil) up to (pseudo-) equilibrium values for all layers. Coalescence pressures are calculated as a measure of coalescence stability.

Acetylation of legumin results in a significant increase of the coalescence stability (about three-fold). The coalescence pressure of the emulsion with the native legumin decreases after a storage period of about 2 months. By contrast, the emulsion prepared from the acetylated legumin shows a higher coalescence pressure, even after about 8 months. This observation is in agreement with the storage stability.

Initial results from applying sedimentation velocity experiments in connection with the method for characterizing the coalescence stability have provided the following results: i) only the 11–12 S protein component in the starting native legumin solution occurred in the separated continuous phase after (incomplete) demulsification. A 15 S aggregate (11%) could no longer be detected in the separated continuous phase. ii) The 16–17 S aggregation component and a lower molecular weight dissociation product (≤2 S, 25–30%) present in the starting solution of acetylated legumin did not occur in the separated continuous phase, but only an aggregated 22–26 S component. This supports the conclusion for a preferred adsorption of low molecular components during preparation of the emulsion.