Compounds from soybeans may improve animal health
Antimicrobial compounds that soybean plants produce when threatened by insects, disease and even drought could help animals stay healthy, reducing the need for antibiotics."When a soybean is attacked by a pathogen, the plant produces phytochemicals called glycerolins as a defense mechanism," says Assistant Professor Bishnu Karki of the Department of Biology and Microbiology at South Dakota State University. His research group identified pathogens and lab-scale processes to trigger glycerolins and began evaluating soybean varieties to see which ones produce higher levels of antimicrobial compounds.
"Animals, such as pigs and poultry, are already consuming diets rich in soybeans and could benefit from the antimicrobial properties of the phytochemicals," Karki said, noting that scientists are studying the impact of glycerolines on human health, particularly with respect to cancer, inflammation and cardiovascular disease.
Karki's research is supported by U.S. Department of Agriculture Hatch Act funding through the South Dakota Agricultural Experiment Station. Two master's students and several undergraduate students also worked on the project.
In the past, antibiotics were incorporated into water and feed to help animals stay healthy and efficiently reach market weight. However, the FDA's Feed Directive, which aims to decrease the development of antibiotic-resistant microorganisms, has recently limited the use of antibiotics to specific health problems. Therefore, livestock producers need natural alternatives, such as glycerol-enriched soybeans, that can provide similar benefits to antibiotics.
Glycerol production
Under normal conditions, glycerolins are not present in soybeans, Karki said. When soybeans are threatened by environmental stressors, such as a fungal infection, the plant responds by producing glycerolins to defend itself.
Karki and her team worked with chemist Mark Berhow of the USDA Agricultural Research Service's Functional Foods Group in Peoria, Illinois, to determine how to maximize glycerolin production in soybeans. The goal was to produce at least three milligrams of glycerol per gram of soybeans, the amount needed to be used as an antimicrobial in swine feed.
The researchers found that dehulled, sprouted and fungus-inoculated soybeans produced higher levels of glycerol than dehulled or halved beans. The soybeans were then freeze-dried and ground to determine glycerol levels. The results, published in the journal Mycological Progress, showed the ability to produce 3.763 mg of glycerol per gram of soybeans.
In a later study, the researchers evaluated a dozen soybean varieties, inoculating them with two varieties of edible fungi and incubating them for up to 120 hours. They found that the fungus Aspergillus sojae produced more glycerol, with levels peaking between 96 and 120 hours of incubation.
In addition, according to Karki, "the soybean variety makes a difference." Although a variety's susceptibility to fungal diseases did not increase production, early maturing varieties tended to produce more glycerolins and exposure to ultraviolet light prior to fungal inoculation improved these results.
The next step will be to test more varieties from different states to identify those with higher potential for glycerol production, and then work with breeders to examine the genetic pathways by which this occurs.
Taking it to the next level
"We have a lab-scale process, but we need to scale it up to demonstrate feasibility," Karki said, noting that testing to ensure the process is reproducible required up to 100 beans. The new POET Bioproducts Institute, located in SDSU's research park, will play a key role in scaling up the technology. The facility is expected to be completed by summer 2023.
"The use of naturally occurring compounds to replace antibiotics could be a game changer for the animal production industry. Through the POET Bioproducts Institute, researchers can work with industry partners to bring promising biotreatment technologies like this to market," said Professor Emeritus Bill Gibbons, associate dean for research in the College of Agriculture, Food and Environmental Sciences and director of the South Dakota Agricultural Experiment Station.
"Glycerol production is better when soybeans are dehulled, but we need to keep the endosperm intact for the seeds to germinate," she continued. "Commercial hulling equipment can crack soybeans, so we need to custom design a machine that can remove the hulls without disturbing the endosperm."
In addition, understanding the metabolic pathways by which soybeans divert energy to produce glycerolins will help scientists manipulate these pathways to increase production of the antimicrobial compound.
"Soybeans are one of the most important commodities in the animal and human nutrition market," Karki said. While glycerol-rich soybeans may have health benefits for animals, they may also have the potential to improve human health.
