Research reveals cause of rapeseed protein bitterness

Rapeseed protein may soon be palatable to humans as the source of the bitter taste has been identified

Christoph Dawid and Corrinna Hald, with a beaker of rapeseed

Researchers at the Technical University of Munich (TUM) have made a discovery that could shake up vegan protein markets. Rapeseed has the most plant-based protein, second-only change to soybeans. The team from TUM have identified the substance that makes protein extracted from rapeseed so bitter. This is a first step towards developing rapeseed for the human protein supply.

Rapeseed doesn't just contain oil but high-quality protein too, which features many essential amino acids. Worldwide, around 1.12 million tonnes of crude protein is produced annually from rapeseed oil. Although farmers have long used this so-called rapeseed cake as a protein feed for animals, it has not played a role as a protein source in human nutrition so far.

One reason is that the accompanying substances contained in rapeseed strongly impair the taste of the obtained protein isolates. These substances include, for example, very bitter-tasting secondary plant constituents. Therefore, the team looked into the issue of which bitter substances cause the rapeseed protein's unpleasant bad taste.

The bitter culprit

The rapeseed plant

The researchers, led by food chemist Thomas Hoffman, investigated three different protein isolates using mass spectrometry and taste tests. The first isolate was an extract of all the proteins contained in rapeseed meal. The second isolate predominantly contained cruciferin Then the third isolate predominantly napin.

Cruciferin and napin are rapeseed's two main storage proteins. All three isolates had a protein content of 80 to 90 percent.

As the investigations show for the first time, a compound called kaempferol 3-O-(2‘‘‘-O-sinapoyl-ß-sophoroside) is the key substance that makes protein extracts from rapeseed unpalletable.

The cruciferin isolate in particular contained a large amount of this bitter substance with 390 mg per kg. The rapeseed meal and napin isolate had less than a tenth of the quantity, but still tasted bitter in the sensory test.

Since we now know the cause of the bitter off-taste, it is much easier to develop suitable technological processes or breeding strategies that can be used to produce tasty, protein-rich foods from rapeseed," said co-author Corinna Dawid, who heads the Phytometabolomics research group at TUM.

The future need for plant-based protein

According to the Food and Agriculture Organization of the United Nations, the demand for food will approximately double by 2050 due to the growing world population. "Bottlenecks are to be expected in this context, particularly in protein supply," says Hofmann, who also heads the Chair of Food Chemistry and Molecular Sensory Science at TUM.

According to Hofmann, it is therefore important to develop new plant protein sources for human nutrition. And rapeseed is a good local source considering the amount that can be produced and its high-quality.

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