Farmers who grow rapeseed for vegetable oil and biodiesel generate mountains of protein-rich meal byproduct that could significantly enrich the diets of livestock and even humans . . . if only it didn’t taste so terrible.
But now, researchers have found a way to engineer rapeseed to make its bitter byproducts easier on the taste buds, opening up new avenues for its use—perhaps even as a replacement for imported commodities like soy in animal and human diets whose production endangers global forests.
Specifically, it’s the “pungent, wasabi-like flavor” that makes rapeseed meal so difficult to stomach, explains Deyang Xu, a researcher in the Department of Plant and Environmental Sciences at Copenhagen University and lead author on the new Nature paper. This unpleasant flavor is caused by compounds called glucosinolates—and not only are these unpalatable, they also pose a health risk of goiter in high quantities, “which is also why there is a limit to how much rape seedcake can be put into feed pellets today,” Xu explains. In fact, food regulatory agencies allow only tiny quantities to be incorporated into pig feed, for instance.
Yet, the solid byproducts of rapeseed oil-pressing—called ‘rapeseed cake’—is so protein-rich that it represents 50% of all the crude protein produced in the European Union (followed by sunflower seeds, pulses, and soybeans). Seeing the potential of this “huge local protein source,” says Xu, the researchers launched their campaign to make more edible rapeseed cake.
Working in the model thale cress plant, a close relative of rapeseed, the researchers first set about identifying a set of proteins that are known to transport glucosinolate compounds into the seed head from productive tissues in the plant. These compounds are actually a defense mechanism in plants, and their spicy, bitter flavor is designed to discourage nibbling animals.
The researchers homed in on three proteins in particular, and then tested whether their hunch was correct—that these are crucial to the bitter accumulation in seed heads—by creating mutant thale cress plants where these proteins were knocked out. They did this using a technique called ‘transport engineering’ that changes the function of the proteins to disable them in the mix.
The experimental knock-outs worked: compared to untouched plants, mutant thale cress contained less than 6% glucosinolate compounds in their seeds, the researchers found. But interestingly, the accumulation of this compound continued elsewhere in the plant—the seeds alone were cleared of its bitter, burning effects.
That’s important because by targeting only the intended areas, this engineering preserves this important evolutionary defense mechanism elsewhere in the plant, maintaining protection against nibbling insects and other animals in the field.
With the idea so far tested and proven in thale cress, the next step will be to engineer this glucosinolate-dampening trait into actual rapeseed plants. Considering the strong genetic relationship between the two plants, Xu is confident that they’ll have similar success.
Once they’ve proved it works, it should lay the foundation for approval from the European Food Safety Authority (EFSA) for the widespread use of rapeseed cake—and not just in livestock feed, but human foods, too. “Rapeseed cake proteins can be used for example in whole food products, in muesli, and in cakes,” says Xu.
This could provide another promising plant-based protein alternative to meat, and it does this using an agricultural waste product from existing crops—which additionally relieves agricultural pressure on the land.
The discovery unlocks a new protein source that marks a potential win for nature, climate, and health. The takeaway? When life gives you bitter compounds, why not engineer them into something tasty and new?
Xu et. al. “Export of defensive glucosinolates is key for their accumulation in seeds.” Nature. 2023.