Half of the vegetable proteins in the European Union come from rapeseed plants. Until now, the plant has only been used for oil and animal feed, as it is bitter and unsafe for human consumption. In a new study published in the journal Nature, University of Copenhagen researchers have moved closer to removing the bitter substances from the plant and, in doing so, paving the way for a new protein source to support the green transition.
Fields covered with yellow carpets are a sure sign of summer. In Denmark, more than 200,000 hectares of rapeseed are now grown for use as edible oils, industrial oils and as a protein supplement for animal feed – but not as a direct food source for humans. While the high content of bitter defensive substances in the rapeseed plant keeps disease and herbivores at bay, it also makes the plant inedible for humans.
Now, a team of scientific researchers from the University of Copenhagen’s Department of Plant and Environmental Sciences has identified the proteins that help store bitter substances in the seeds of cress, a typical plant and close relative of rapeseed. The new research result has been published in the scientific journal nature.
Knowledge can be used to remove these proteins, and in doing so, the bitter taste of rapeseed, which provides a lot of opportunities. In fact, half of the domestic vegetable proteins in the European Union already come from rapeseed plants.
“The climate crisis requires that we reduce meat consumption and eat more plants, as rapeseed has great potential as a new source of vegetable protein in the green transition. Our latest research findings bring us a crucial step closer towards the full utilization of rapeseed,” says Professor Barbara Ann Halkier, who led the research.
The substances in wasabi and mustard are gone
The defensive substances of rapeseed are called glucosinolates and are known for the spicy flavors in wasabi and mustard. As a result, the so-called rapeseed cake, the remains of the seeds after pressing the oil, was used only in limited quantities as feed for pigs and chickens, despite its impressive protein content of 30-40%.
The researchers succeeded in removing the bitter defensive substances by identifying the three proteins in the plant that are responsible for transporting the substances to its seeds. The new knowledge makes it possible to prevent the accumulation of these substances in the seed by removing the proteins via a technique called “transfer engineering”. As such, defensive substances remain in all other parts of the plant, allowing it to continue to defend itself.
“Our research shows that the attachment — a kind of umbilical cord — that exists between the seed and the surrounding fruit rind is a cellular factory to produce glucosinolates that end up in the seed. They can only get away when there is danger. They need to produce several defense substances to protect themselves. from attacks by diseases and herbivores. Our discovery allowed us to find a way to get rid of these bitter substances from the seeds,” said Dr. Diang Xu, lead author of the new study.
A breakthrough ten years in the making
So far, the researchers have shown that their method works in cress (Arabidobsis thaliana), a model plant closely related to the rapeseed plant.
“The next task is to show that we can transfer our findings from Arabidopsis to a closely related rapeseed plant, which we are working on now,” says Dr. Xu.
The research that led to this discovery is the result of a long haul made possible by a 10-year grant from the Danish National Research Foundation to the DynaMo Center in the Department of Plant and Environmental Sciences of the Faculty of Science.
“I can’t stress enough how important this long-term grant was to us in order to achieve this key research outcome. It really allowed us time to immerse ourselves in the details and the geeks, which paid off,” says Barbara Ann Halkyr.
Facts about plant defenses
Cruciferous plants are characterized by their ability to produce a group of defensive substances called glucosinolates. These substances give plants such as broccoli, cabbage, watercress, and rapeseed a strong, bitter taste that repels herbivores and disease.
To protect their offspring, cress and rapeseed plants fill their seeds with glucosinolates so that the seeds and young seedlings can defend themselves against insects and other enemies. Since the seeds cannot synthesize glucosinolates themselves, the substances must be transferred from the parent plant to the seeds.
Some glucosinolates are healthy, such as those found in broccoli and other cabbage. However, the glucosinolates found in rapeseed are unhealthy.