Current agronomic practices, harvest & post-harvest processing of soybeans (Glycine max)- A review

Authors: Toomer, Ondulla; OVIEDO, EDGAR - North Carolina State University; MUHAMMAD, ALI - North Carolina State University; PATINO, DANNY - North Carolina State University; JOSEPH, MICHAEL - North Carolina State University; FRINSKO, MIKE - North Carolina State University; Vu, Thien; MAHARJAN, PRAMIR - Tennessee State University; Fallen, Benjamin; Mian, Rouf

Submitted to: Agronomy Journal
Publication Type: Review Article
Publication Acceptance Date: 1/27/2023
Publication Date: 1/31/2023
Citation: Toomer, O.T., Oviedo, E.R., Muhammad, A., Patino, D., Joseph, M., Frinsko, M., Vu, T.C., Maharjan, P., Fallen, B.D., Mian, R.M. 2023. Current agronomic practices, harvest & post-harvest processing of soybeans (Glycine max)- A review. Agronomy Journal. 13(2):427. https://doi.org/10.3390/agronomy13020427.
DOI: https://doi.org/10.3390/agronomy13020427

Interpretive Summary: Soybeans are a leguminous crop, primarily grown in the U.S. Midwest for oil extraction, leaving the remaining soy cake as a source of highly digestible amino acids. Interestingly, only 2% of globally produced soybean meal is used for food, while the remaining 98% of globally produced soybean meal is used for animal nutrition, with poultry consuming 64% of U.S. produced soybean meal. Soybeans contain highly digestible protein and are processed using various thermal and mechanical processing methods prior to the inclusion in animal diets. Raw soybeans and soybean meal contain anti-nutritional factors (trypsin inhibitors, lectins, saponins) that adversely affect animal growth performance and health, which are destroyed with optimal thermal processing. This manuscript reviews current agronomic practices, harvest & post-harvest processing of soybeans as well as analytical methods utilized to define optimal soybean meal processing methods (nitrogen solubility index, protein dispersibility index, urease activity, and protein solubility in potassium hydroxide) to eliminate anti-nutritional factors found in raw soybeans and/or soybean meal, while maintaining soybean meal protein quality and nutrient bioavailability.

Technical Abstract: Globally, soybeans are grown to meet the needs for animal and human nutrition, oil extraction, and use in multiple industrial applications. Decades of soybean research, innovative farming methods, and the use of higher yielding resistant seed varieties have led to increased crop yields. Globally, soybean producers have utilized enhanced processing methods to produce nutritious high-quality meal and extracted oil for use in animal feed and within the food industry. Soybeans contain highly digestible proteins and are processed using various mechanical and chemical techniques to produce high quality animal feed ingredients. Defatted soybean meal (DSM) is usually prepared by the solvent extraction process of soybeans, whereby almost all oil content is removed. When oil is not extracted, full-fat soybean meal (FFSBM) is created. This form provides an excellent source of dietary energy by retaining the lipid component and is very useful in animal feeds by reducing the need for adding exogeneous lipids. However, some anti-nutritional factors (ANF) are present in FFSBM if not properly heat treated before inclusion in the finished feed. These ANF adversely affect the internal organ function and overall growth performance of the animal. Among these ANF, protease inhibitors are most important, but can be readily destroyed with optimal thermal processing. However, if the process protocols are not followed precisely, excessive heat treatment may occur, resulting in both reduced protein quality and amino acid bioavailability in the meal. Conversely, insufficient heat treatment may result in the retention of some ANF in the meal. Thermally resistant ANF can be greatly reduced in the bean and meal when dietary enzyme supplementation is included in the finished feed. This approach is cost-effective and most commonly utilized commercially. After processing, the soybean meal quality is often measured using in vitro methods performed at commercial analytical laboratories to assess the nitrogen solubility index (NSI), protein dispersibility index (PDI), urease activity (UA), and protein solubility in potassium hydroxide. Once properly processed, FFSBM or DSM can be utilized optimally in the diets of poultry and aquaculture to enhance the economic viability, animal nutrition, production performance, and the quality and nutritional value of the meat and/or eggs produced.