University of Illinois - Urbana - Champaign; Sharita Forrest, Feb 17, 2023
A protein in soybeans blocks production of a liver enzyme involved in the metabolism of triglycerides and low-density lipoprotein, scientists found in a recent study.
Consuming soy flour rich in the protein B-conglycinin has the potential to reduce low-density lipoprotein – LDL – cholesterol levels and reduce the risk of metabolic diseases such as atherosclerosis and fatty liver disease, said Elvira de Mejia, a professor of food science and human nutrition at the University of Illinois Urbana-Champaign.
Scientists have long known of soybeans’ cholesterol-reducing properties and lipid-regulating effects. Researchers in the recent project at the University of Illinois investigated two soy proteins thought to be responsible for the outcomes – glycinin and B-conglycinin. They found the latter to be particularly significant.
“Soybeans’ effects on cholesterol metabolism are associated with their protein concentrations and composition,” de Mejia said. “They’re also associated with peptides embedded in them that are released during gastrointestinal digestion.”
The team defatted and ground into flour 19 soybean varieties, each of which contained differing proportions of the two proteins. The proportion of glycinin in the varieties ranged from 22 percent to 60 percent. The proportion of the B-conglycinin ratio ranged from 22 percent to 52 percent.
Using a simulation of the human digestive process validated by other studies, the team sequentially mixed the defatted soybean flours with various fluids and enzymes to mimic the oral, gastric, intestinal and colonic phases of digestion. They identified 13 bioactive peptides produced during digestion, most of which came from glycinin and B-conglycinin.
When testing the digested materials’ capacity to inhibit the activity of HMGCR, a protein that controls the rate of cholesterol synthesis, the researchers found their inhibitory properties were two-to-seven times less potent than simvastatin, a drug used to treat high LDL cholesterol and fat levels in the blood. Simvastatin was used as a control in the study.
After classifying the soybean varieties by their glycinin and B-conglycinin composition and their HMGCR inhibitory properties, the team selected five varieties for further analysis.
“We started with cells that were already exposed to fatty acids to mimic fatty liver disease and tried to understand the role of the digested soy proteins,” de Mejia said. “We measured several parameters associated with cholesterol and lipid metabolism and various other markers – proteins and enzymes – that positively or negatively affect lipid metabolism.”