[Protein isolation by means of complexing agents. 2. Formation of insoluble complexes of sunflower albumins with alginate or pectin].
The formation of insoluble complexes of sunflower seed albumin and alginate or pectin is studied by means of turbidimetric titration and by determining the pH-dependent precipitability of protein. The complex formation that is based on electrostatic interaction is a function of the pH value and the protein-polyanion ratio. Consequently, it is affected by the neutral salt content of the solutions. 90% and more of the dissolved protein may be precipitated if the proportion of the precipitant amounts to 20%. A sodium chloride content of 0.6% reduces the precipitability by alginate to 74%. In the presence of 0.3% sodium chloride, at most 55% of protein are still precipitated by pectin. The difference in strength between the albumin-alginate and the albumin-pectin complex is also expressed by the dye-binding power. Albumin-pectin complexes bind the same amount of amido black as free protein. On the contrary, albumin-alginate complexes exhibit reduced dye-binding power due to stronger binding of the protein to the polyanion. The results obtained by turbidimetric titration of model systems can, in principle, be extrapolated to the precipitation of albumins from protein extracts. In accordance with the heterogenicity of the protein, the turbidimetric titration of the albumin-alginate and the albumin-pectin complexes exhibits two maxima.