The effect of Sodium Dodecyl Sulfate on the ethanolic fractionation of dilute gelatin solutions

Abstract

Gelatin is a heterogeneous protein with a broad molecular weight profile (MWP), which determines its behaviour in solution. Addition of a non-solvent, such as ethanol, to aqueous gelatin solutions causes progressive desolvation of the polymer. When sufficient solvent molecules are removed, the gelatin molecules begin to aggregate, resulting in phase separation, and forming a coacervate or, if sufficient desolvation occurs, a precipitate.1 Sodium dodecyl sulphate (SDS) associates with gelatin through hydrophobic interactions involving the hydrocarbon tail, and through ionic interactions between the negatively charged headgroup of SDS and positively charged side groups on the gelatin molecule; both mechanisms cause unfolding of the protein and yield a hydrophobic complex.2 It can be hypothesised that addition of SDS to dilute gelatin solutions will affect their desolvation behaviour, depending on the degree of binding of SDS to gelatin at different pH’s. The objective of this work was to determine the effect of dilute SDS concentrations on the response of B225 gelatin to the non-solvent ethanol at different pH’s.