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Rapeseed protein extracts’ bitter off-taste attributable to kaempferol
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Friday, 01 February, 2019, 14 : 00 PM [IST]
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Munich
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Rapeseed does not just contain oil, but high-quality protein, too. And these contain many essential amino acids.However, the protein extracts from rapeseed have an intense, bitter off-taste. This is attributable to a compound called kaempferol 3-O-(2‘‘‘-O-sinapoyl-ß-sophoroside).
This was identified by a team led by Thomas Hofmann, food chemist and head, Chair of Food Chemistry and Molecular Sensory Science, Technical University of Munich (TUM), and was a first step towards developing rapeseed for the human protein supply.
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.
“Bottlenecks are to be expected in this context, particularly in protein supply,” said Hofmann, who is also director, Leibniz-Institute for Food Systems Biology.
“It is, therefore, important to develop new plant protein sources for human nutrition. And rapeseed is a good local source,” he added.
No role of rapeseed protein in human nutrition
Worldwide, about 1.12 million tonne of crude protein are 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.
Hofmann and his team, therefore, looked into the issue of which bitter substances cause the rapeseed protein’s unpleasant bad taste.
Three protein isolates
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 per cent.
The cruciferin isolate in particular contained a large amount of this bitter substance with 390mg per kg. The rapeseed meal and napin isolate had less than a tenth of the quantity, but still tasted bitter in the sensory test.
Starting point for new processes
“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.
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