Protein solubility at different pHs
The plot of protein solubility at different pH extractions (Fig. 2) shows a typical bowl-shaped curve. Protein solubility was highest (70%) at pH 10. The minimum protein solubility ranged from pH 4 to 5.5 where 9-10% of the protein remained in solution. Alkali protein extraction is usually carried out at pH 9 to minimize the production of lysinoalanine, which occurs at high pH values and temperatures (Lusas and Rhee, 1995). Lysinoalanine causes reduced protein nutritional quality and digestibility in rodents and primates (Friedman, 1999). For silflower, the protein solubility at pH 9 is about 62%, which is 11.4% lower than at pH 10.