Improved emulsion stability by succinylation of patatin is caused by partial unfolding rather than charge effects

This study investigates the influence of succinylation on the molecular properties (i.e. charge, structure and hydrophobicity) and the flocculation behavior of patatin-stabilized oil-in-water emulsions. Patatin was succinylated to five degrees (0% (R0) to 57% (R2.5)). Succinylation not only resulted in a change of the protein charge but also in (partial) unfolding of the secondary structure, and consequently in an increased initial adsorption rate of the protein to the oil-water interface. The stability against salt-induced flocculation showed two distinct regimes, instead of a gradual shift in stability as expected by the DLVO theory. While flocculation was observed at ionic strengths >30 mM for the emulsions stabilized by the variants with the lowest degrees of modification (R0-R1), the other variants (R1.5-R2.5) were stable against flocculation ≤200 mM. This was related to the increased initial adsorption rate, and the consequent transition from a protein-poor to a protein-rich regime. This was confirmed by the addition of excess protein to the emulsions stabilized by R0-R1 which resulted in stability against salt-induced flocculation. Therefore, succinylation of patatin indirectly results in stability against salt-induced flocculation, by increasing the initial adsorption rate of the protein to the oil-water interface, leading to a shift to the protein-rich regime.