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

Authors: Liu, Keshun; SEAGERS, SUSAN - Bunge, Ltd; Hojillaevangelist, Milagros; PALLARES, ANDREA - Desmet; WU, XIN - American Oil Chemists' Society (AOCS)

Submitted to: Sustainable Food Proteins
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/12/2024
Publication Date: 12/11/2024
Citation: Liu, K., Seagers, S., Hojillaevangelist, M.P., Pallares, A.P., Wu, X. 2024. International collaborative study on measuring protein solubility index for legumes, oilseeds, cereals and related products. Sustainable Food Proteins. 2:236–249. https://doi.org/10.1002/sfp2.1039.
DOI: https://doi.org/10.1002/sfp2.1039

Interpretive Summary: Proteins are important components of almost all food and feed products. Descriptions of protein quality often refer to their nutritional values and/or functional properties. Among many factors that affect protein quality, the degree of heating is most impactful. Both under and over-heating can result in poor nutritional values. For this reason, in the animal nutrition field, an in vivo study with live animals is often conducted to assess protein quality. Yet, in vivo methods are rather expensive, time consuming, and cost prohibitive. Therefore, decades ago, several simple methods were developed to measure protein solubility of various products for food or feed uses, including nitrogen solubility index (NSI), protein dispersibility index (PDI), and protein solubility in 0.2% potassium hydroxide. Unfortunately, these methods are outdated and have some practical issues. Consequently, two years ago, researchers at USDA-ARS, Aberdeen, Idaho, developed a new protein solubility index (PSI). It features protein extraction with 0.02% sodium hydroxide, nitrogen measurement on dried residues, and simultaneous running of multiple samples. With increasing demand for alternative proteins to replace animal proteins in food and feed, there is a renewed interest in measuring protein solubility of existing and novel sources such as those found in plants, bacteria, fungi, and insects. A method that is official and can accurately and cost-effectively measure protein solubility is rather important for food and feed industries. Consequently, the new PSI method was proposed as an American Oil Chemists Society (AOCS) Method, Ba 15-2023. To meet the AOCS official method approval requirements, researchers at USDA-ARS, Aberdeen, Idaho, continued their efforts by conducting an international collaborative study consisting of 16 labs and 13 coded samples of soybeans, pulses, cereals, and their processed products. Results indicated that, using the newly developed AOCS method, 16 labs were able to produce PSI values with excellent repeatability and good reproducibility. Therefore, the study validated the performance of the proposed AOCS method and demonstrated that PSI could serve as a simple and unified protein quality parameter for food, feed, and related industries; thereby, eliminating the need for multiple procedures and terminologies. In July, 2024, after reviewing the results of the international collaborative study, AOCS Uniform Method Committee approved the proposed method the the AOCS Official Method Ba 15-2023 for measuring PSI in legumes, oilseeds, cereals and related products. The method is now available at the AOCS website https://library.aocs.org/Ba-15-2023/

Technical 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.