An international collaborative study on the new AOCS proposed method Ba 15-2023 for measuring protein solubility index

Protein quality affects nutritional values and functional properties of protein products. It is important to assess protein quality accurately and cost-effectively. Recently, a new indicator for protein quality, protein solubility index (PSI), was developed (J. Am. Oil Chem. Soc. 2022; 99, 855–871). The method features 5 mM alkali hydroxide extraction with magnetic stirring and simultaneous running of multiple samples. It was proposed as AOCS Method Ba 15-2023. As a part of the AOCS method approval process, a collaborative study was conducted to evaluate the performance of the proposed method. It involved 16 laboratories from 10 countries to measure PSI of 12 selected samples plus a blind duplicate, including soybeans, pulses, cereals, and their processed products (flours, concentrates and isolates). After rigorous statistical treatment to remove a few outliers, several precision parameters were calculated. Repeatability relative standard deviations (RSDr) ranged 0.6 - 11.4%, with 10 samples having RSDr ≤ 5%. Reproducibility RSDR ranged 2.6 - 15.7%. The five samples with RSDR ≥10% were limited to those with the lowest N content, the lowest PSI, or protein isolates. The study demonstrated robust performance of the proposed AOCS method. A few collaborators carried out additional experiments to address some aspects of the method, leading to further improvement. The proposed method is undergoing evaluation by AOCS Uniform Methods Committee for adoption as Official Method for measuring PSI in various protein products. It is poised to serve as a unified index for protein quality with respect to both nutritional values and functional properties.