Protein solubility index (PSI): a new simple and unified index for measuring plant protein quality

Authors: Liu, Keshun

Submitted to: Annual Meeting and Expo of the American Oil Chemists' Society
Publication Type: Abstract Only
Publication Acceptance Date: 2/23/2023
Publication Date: 5/2/2023
Citation: Liu, K. 2023. Protein solubility index (PSI): a new simple and unified index for measuring plant protein quality. Annual Meeting and Expo of the American Oil Chemists' Society. Available. https://aocs.eventscribe.net/SearchByBucket.asp?f=TrackName&pfp=BrowsebyBucket.

Interpretive Summary:

Technical Abstract: There has been increased use of plant proteins as food, feed, and industrial materials in recent years. Broadly speaking, protein quality affects nutritional values and functional properties of a protein product. For better utilization, it is important to assess protein quality accurately and cost-effectively. One major factor affecting protein quality is the degree of protein denaturation, which relates directly to the degree of heating. Unfortunately, it is difficult to precisely measure structural changes of protein molecules resulting from heat denaturation, while assessing protein quality in vivo is costly and time-consuming. Therefore, for decades, several indirect indices have been relied upon, including nitrogen solubility index (NSI), protein dispersibility index (PDI), urease activity, and protein solubility in 0.2% potassium hydroxide. However, since these methods were developed some 70 years ago, they either require specific equipment that is expensive, outdated, or unavailable and/or are limited to certain products or applications, while different procedures and terminologies often cause confusion. To address these issues, we have recently developed a new protein quality index, hereby referred to as the protein solubility index (PSI), after investigating many relevant factors that centered on two major stages: protein extraction and nitrogen analysis. The new method features 5 mM alkali hydroxide extraction with magnetic stirring at room temperature for 1 hour, nitrogen analysis of dried residues, and small sample size. There is a strong correlation between PSI and activity of trypsin inhibitors in soy protein products. Trypsin inhibitor is considered the best quality index due to its proteinaceous nature and antinutritional effect. Hopefully, PSI can serve as a unified index to replace most, if not all, of the indirect indices currently used for protein quality measurement. With easy performance and good repeatability, this would eliminate confusion of multiple tests and terminologies used currently by relevant industries and scientific communities.