Scientists at the Technical University of Munich (TUM) have made a discovery that can shake up the vegetarian protein markets. Rapeseed has the most plant-based protein - the second-only change to soybeans. The team from TUM has spotted the material that makes protein extracted from the rapeseed so sour or bitter. This is a first step towards developing rapeseed for the human protein supply.
According to Professor Thomas Hofmann of TUM, who is also Director of the Leibniz Institute for Food Systems Biology, it is important to develop new plant protein sources for human nutrition. And rapeseed is a good local source.
Rapeseed does not just contain oil but also a high-quality protein that contains many necessary amino acids. Worldwide around 1.12 million tons of crude protein are produced yearly 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. Hofmann and his team, therefore, looked into the issue of which bitter substances cause the rapeseed protein's unpleasant bad taste.
The researchers investigated 3 different protein isolates using mass spectrometric analysis methods and taste tests. The 1st isolate was an extract of all the proteins contained in rapeseed meal. The 2nd isolate predominantly contained cruciferin and the third napin, which are the rapeseed's two main storage proteins. All three isolates had a protein content of 80 to 90 %.
As the investigations show for the first time, a compound called kaempferol 3-O-(2'''-O-sinapoyl-ß-sophoroside) is the main substance that makes protein extracts from rapeseed inedible. The cruciferin isolate, in particular, contained a large amount of this bitter substance with 390 milligrams per kilogram. The rapeseed meal and napin isolate had less than a 10th 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.
