Natural aging of soybean impacts ingredient functionality of soy protein isolates

Authors: Shea, Zachary; TENG, ZHOUTAI - North Carolina State University; Taliercio, Earl; HAOTIAN, ZHENG - North Carolina State University

Submitted to: Journal of the American Chemical Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/8/2025
Publication Date: 12/31/2025
Citation: Shea, Z.A., Teng, Z., Taliercio, E.W., Haotian, Z. 2025. Natural aging of soybean (Glycine max) impacts ingredient functionality of soy protein isolates. Journal of the American Chemical Society. https://doi.org/10.1021/acsfoodscitech.5c00909.
DOI: https://doi.org/10.1021/acsfoodscitech.5c00909

Interpretive Summary: Soybean is an important crop due to its excellent nutrient profile, environment sustainability, and uses in the alternative protein market for human consumption in foods, such as tofu. While there is a lot of work that has been done to understand how various aspects, such as method of protein extraction, defatting solvent, and environment can impact protein usage in the alternative protein market, little has been done to determine how storage can impact utility of soy protein as a functional ingredient as a substitute for animal protein. This is important as soybean seed can be stored for over a year before being using the the alternative protein market. To accomplish this, protein was extracted from the NC-Dunphy soybean variety from seed stored for 0, 1, 3, and 4 years and water-holding capacity, oil-holding-capacity, solubility, foaming, and emulsion stability were measured. Soybean stored for longer had significantly reduced foaming stability and water-holding capacity with recently harvested seed having up to double the foaming stability and triple the water-holding capacity than older seed. Oil-holding capacity, solubility, and emulsion stability did not have any significant differences between years. This findings indicate that storage time can significantly impact some protein functionalities and that soybean should be used earlier rather than stored for a long time if it is going to be used in the alternative protein market.

Technical Abstract: Soybean is a globally significant crop due to its high protein and oil content, superior protein functionality, and sustainable production compared to other plant proteins, making it ideal for the expanding plant protein industry. However, research is needed to understand how the age of soybean seeds impacts the functionality of the extracted protein as a food ingredient. To accomplish this, protein was extracted from the NC-Dunphy genotype harvested in 2019, 2020, 2022, and 2023. The extracts were freeze dried to obtain soy protein isolates (SPI). All SPI samples had a moisture content no higher than 5% (w/w) and a protein content of no less than 85% (w/w). The characteristics and functionalities of SPI solutions were studied. For instance, solubility, colloidal stability, particle size, foaming properties, emulsifying properties, and water- and oil-holding capacities (WHC and OHC) were determined to evaluate the ingredient functionality for all SPI samples. SPI from 2023 exhibited superior WHC and emulsifying properties (emulsion stability) compared to SPI derived from longer aged soybeans. For example, SPI-2023 had a WHC of 6 g water g'¹ protein whereas the WHC was around 2 g water g'¹ protein for other SPI. Compared to SPI-2019, SPI extracted from 2023, 2022, and 2020 soybeans were more functional in stabilizing foam. The functionality results suggest that soybean aging period may affect interfacial property related functionalities for SPI such as emulsion stability and foam stability; whereas the basic characteristics of protein sol such as solubility and sedimentation stability were not affected.