Protein solubility characteristics of commercial soy protein products

Solubility characteristics of commercial soy protein products (flours, concentrates, and isolates) were determined under various conditions. From the solubility profiles at various pH values and NaCl concentrations, soy protein isolates can be divided into three groups. One group had high solubility near the pl. Another group had low solubility near the pl, but high solubility at pH 11. The third group had low solubility even at pH I I. Except for the hydrolyzed products, the protein solubilities of the soy protein products at various salt concentrations were very low. Temperature did not significantly affect the protein solubility, although a few products showed more than a 20% increase at temperatures > 50degreesC. Soy protein concentrates and soy protein isolates showed similar solubility profiles. The proteins in all commercial products (except flours) tested were denatured, as evident from the solubility profiles in the presence of salt and the enthalpy values from DSC.