The effect of sodium chloride on ethanolic fractionation of dilute gelatin solutions

Abstract

Gelatin is the denaturation product of the protein collagen, the main constituent of animal skin, bone, and connective tissue. The conversion of collagen to gelatin results in a heterogeneous product with a broad molecular weight profile (MWP), which is important in determining the behaviour of the protein in solution. Addition of successive increments of a non-solvent, such as ethanol, to gelatin solutions causes the Florey- Huggins solvent-protein interaction parameter, χ, of the system to successively exceed the critical value for the different molecular weight fractions, causing 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. Modification of the net charge of the protein molecules, by adjusting the solution pH to values ranging about the iso-electric point (IEP), influences the degree of interaction between the different molecular weight fractions, and hence the response of the protein to non-solvent.1 It can be hypothesised that alteration of the molecular charge intensity by changes in the ionic strength of the solution would affect the overall response of the protein. The objective of this work was to determine the effect of dilute NaCl concentrations on the response of B225 and B75 gelatins to the non-solvent ethanol at different pH’s.