Identifying the key substance that makes rapeseed protein taste bitter.
Rapeseed does not just contain oil but high-quality protein, too. However, protein extracts from rapeseed have an intense, bitter off-taste.
A team led by food chemist and chair of food chemistry and molecular sensory science at the Technical University of Munich (TUM), Thomas Hofmann has identified the substance that is pivotal for the bitter taste. This is a first step towards developing edible rapeseed for the human protein supply.
Rapeseed contains many essential amino acids. 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 very bitter-tasting secondary plant constituents.
The researchers investigated three different protein isolates using mass spectrometric analysis methods and taste tests. The first isolate was an extract of all the proteins contained in rapeseed meal. The second 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 percent.
A compound called kaempferol 3-O-(2‘‘‘-O-sinapoyl-ß-sophoroside) is the key 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 kilogramme. The rapeseed meal and napin isolate had less than a tenth of the quantity, but still tasted bitter in the sensory test.
According to the Food and Agriculture Organization of the United Nations (FAO), the demand for food will approximately double by 2050 due to the growing world population. Hofmann says it is therefore important to develop new plant protein sources for human nutrition.
With the knowledge on what was causing the bitter off-taste, researchers can now develop suitable technological processes or breeding strategies that can be used to produce tasty, protein-rich foods from rapeseed.
The research project was funded by the Federal Ministry of Education and Research (BMBF) as part of the RaPEQ project. [APBN]