Cereal Chem 53:902 - 909.  |  VIEW ARTICLE
Soy Protein Solubility: The Effect of Experimental Conditions on the Solubility of Soy Protein Isolates.

J. L. Shen. Copyright 1976 by the American Association of Cereal Chemists, Inc. 

For heterogeneous amorphous proteins, there cannot be a thermodynamically defined solubility at a given temperature and pressure. Instead, the solubilities of these proteins are dependent upon experimental conditions. In order to compare data from the different solubility methods now in use, we have made a systematic study of the effects of experimental conditions upon the solubilities of a freeze-dried, acid- precipitated soy curd, of three commercial soy isolates, and of a commercial sodium caseinate. Significant effects (as much as a 30% change in the solubility) that varied from isolate to isolate were caused by increasing the blending speed from mild shaking to high-speed blending at 11,000 rpm, or by changing from low-force centrifugation to centrifugation at 200,000 x g for 3 hr. Protein solubilities, however, were not affected by initial protein concentration or by equilibrium times longer than 100 min. Increasing temperature from 25 to 62 C raised the solubilities of some of the isolates significantly (8-14%). The Biuret reaction was used to determine "protein solubility" instead of "nitrogen solubility" as determined by Kjeldahl.