The effect of temperature, pH and SDS on the ethanolic fractionation of dilute gelatin solutions

Abstract

The broad molecular weight profile (MWP) of the gelatin in solution, determines its behaviour in solution. The response of gelatin to a non-solvent is affected by the net charge of the molecule, which is determined by the pH of the solution. Thus the interaction of aqueous gelatin with sodium dodecyl sulfate (SDS) which is dependant on the net charge of the molecule should affect the overall behaviour of the solution in response to non-solvent change. The response of type B gelatin solution of Bloom Strength 225 to progressively increasing concentration of ethanol was investigated under various condition of pH, temperature and SDS concentration. It was observed that gelatin solution below the isoelectric point (IEP), where gelatin molecules bear a net positive charge, showed at certain temperature a primary and secondary desolvation process, while gelatin solution with pH above IEP, where gelatin molecules have a net negative charge showed only one desolvation process. This shows that in the presence of SDS, the degree and mechanism of SDS binding to gelatin are affected by the solutions pH. An increase in SDS concentration was observed to affects both the precipitation behaviour of gelatin and response to non-solvent. An increase in SDS concentration gave a higher precipitability of gelatin for both primary and secondary desolvation phenomena and a greater reluctance for gelatin to precipitate with increase in non-solvent ethanol. It was noted that apart from the combined effect of surfactant binding and the net charge of the molecule, the temperature effect was highly influential on the response of gelatin to non-solvent ethanol and the binding of SDS to the gelatin. This latter effect overrides the precipitation behaviour due to SDS concentration and non solvent