Evaluation of a low-resource soy protein production method and its products

Authors: GULKIRPIK, ECE - University Of Illinois; DONNELLY, ANNETTE - University Of Illinois; NOWAKUNDA, KEPHAS - National Agricultural Research Laboratories; Liu, Keshun; ANDRADE LABORDE, J - University Of Florida

Submitted to: Frontiers in Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/17/2023
Publication Date: 4/20/2023
Citation: Gulkirpik, E., Donnelly, A., Nowakunda, K., Liu, K., Andrade Laborde, J.E. 2023. Evaluation of a low-resource soy protein production method and its products. Frontiers in Nutrition. 10. Article 1067621. https://doi.org/10.3389/fnut.2023.1067621.
DOI: https://doi.org/10.3389/fnut.2023.1067621

Interpretive Summary: Developing sustainable, economical, and green technologies to process nutritious food products from locally available sources is one of the key approaches to achieve zero hunger in Sub-Saharan Africa (SSA). Soybean protein is an inexpensive, high-quality source of protein that may help reduce malnutrition in SSA, but it is underutilized for human consumption. In SSA, mechanical expellers remove most soybean oil, leaving 6-13% oxidizable oil in the cake. Soy protein concentrate (SPC) can be made from soy cake, but its production in SSA is constrained because of insufficient processing capabilities, high cost, and complexity of existing processes. A few years ago, a less expensive and low-resource method to prepare SPC was developed by USDA-ARS scientist at Aberdeen, Idaho. This alternative method uses limited resources and water as a leaching solvent instead of aqueous alcohol or acid solution used currently for commercial production of SPC. It is also amenable for the use of soy cake as a starting material. The technology was later transferred to Soybean Innovation Lab (SIL) at University of Illinois for fighting malnutrition in SSA. Recently, scientists at the University of Illinois SIL and the same USDA-ARS scientist at Aberdeen, Idaho, conducted new research to evaluate feasibility of the alternative method to produce SPC from mechanically processed soy cake and to characterize resulting SPC in terms of protein quality and oxidative stability. Results show that using the soy cake as the starting material, the low-resource USDA method produced SPC with a higher protein content, higher protein digestibility, higher crude fiber, and higher oxidative stability, but with lower amounts of oil, phytic acid, and total carbohydrates. This high protein ingredient can be used to fortify basic staple dishes in the SSA region and address protein gaps in growing children.

Technical Abstract: Introduction: One key approach to achieve zero hunger in Sub-Saharan Africa (SSA) is to develop sustainable, affordable, and green technologies to process nutritious food products from locally available sources. Soybeans are an inexpensive source of high-quality protein that may help reduce undernutrition, but it is underutilized for human consumption. This research evaluated the feasibility of a low-cost method developed initially at the United States Department of Agriculture to produce soy protein concentrate (SPC) from mechanically pressed soy cake and thus create a more valuable ingredient to improve protein intake in SSA. Methods: The method was initially tested in the bench scale to assess process parameters. Raw ingredients comprised defatted soy flour (DSF), defatted toasted soy flour (DTSF), low-fat soy flour 1 (LFSF1; 8% oil), and LFSF2 (13% oil). Flours were mixed with water (1:10 w/v) at two temperatures (22 or 60°C) for two durations (30 or 60 min). After centrifugation, supernatants were decanted, and pellets were dried at 60°C for 2.5 h. Larger batches (350 g) of LFSF1 were used to examine the scalability of this method. At this level, protein, oil, crude fiber, ash, and phytic acid contents were measured. Thiobarbituric acid reactive substances (TBARS), hexanal concentration and peroxide value were measured in SPC and oil to evaluate oxidative status. Amino acid profiles, in vitro protein digestibility, and protein digestibility corrected amino acid score (PDCAAS) were determined to assess protein quality. Results: Bench scale results showed accumulation of protein (1.5-fold higher) and reduction of oxidative markers and phytic acid to almost half their initial values. Similarly, the large-scale production trials showed high batch-to-batch replicability and 1.3-fold protein increase from initial material (48%). The SPC also showed reductions in peroxide value (53%), TBARS (75%), and hexanal (32%) from the starting material. SPC’s in vitro protein digestibility was higher than the starting material. Conclusion: The proposed low-resource method results in an SPC with improved nutritional quality, higher oxidative stability, and lower antinutrient content, which enhances its use in food-to-food fortification for human consumption and is thus amenable to address protein quantity and quality gaps among vulnerable populations in SSA.