International collaborative study on measuring protein solubility index for legumes, oilseeds, cereals, and related products

Abstract

Protein quality affects nutritional value 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 (JAOCS, 2022; 99, 855–871). The new method, featuring 5 mM NaOH extraction with magnetic stirring and simultaneous running of multiple samples, was proposed as AOCS method Ba 15‐2023. As part of the AOCS method approval process, a collaborative study was conducted to evaluate its performance. It involved 16 laboratories from 10 countries to measure PSI of the 12 selected samples plus a blind duplicate, including soybeans, pulses, cereals, and their processed products (flours, concentrates and isolates). After rigorous statistical analysis 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% corresponded to protein isolates or those with the lowest N content or the lowest PSI. 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 results of the present study were presented to the AOCS Uniform Methods Committee for evaluation. Once the method is adopted as the 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 value and functional properties.