A Collaborative Study to Develop a Standardized Food Protein Solubility Procedure

Abstract

ABSTRACT A colaborative study was conducted to develop a rapid, simple and reliable procedure for determining the solubility of food protein products, e.g., spray‐dried whey protein concentrate, sodium caseinate, egg white protein and soy protein isolate. The procedure was developed by modifying the nitrogen solubility index (NSI) procedure. Protein content and soluble protein were determined by micro‐Kjeldahl or biuret procedures with standard deviations of 0.83‐4.12 for all proteins except caseinate which had a value of 13.95. Although the biuret and micro‐Kjeldahl procedures generally provided comparable accuracy and precision for protein content and solubility of certain proteins, the biuret procedure exhibited considerable error and variability for other proteins.