As a step in the biosynthesis of sinapine the UDP-glucose:sinapate
glucosyltransferase catalyses the conversion of sinapic acid to
sinapoyl glucose.
A number of plant components including sinapic acid esters restrict
the use of oilseed rape products in human and animal nutrition.
In oilseed rape these compounds are present in much higher
concentrations than in other oil-rich seeds, which accounts for the
bitter taste and astringency of oilseed rape products. The phenolic
compounds present in oilseed rape can form complexes with the
oilseed rape protein, thus reducing the high nutritional value of
the protein. Moreover, these phenolic compounds give rise to an
undesirable dark colouration of oilseed rape protein products.
Sinapic acid esters, which mainly consist of the bitter substance
sinapine (or sinapoyl-choline), normally make up 1-2% of rapeseed
meal. Sinapine is the most frequently occurring phenolic acid ester
compound, accounting for approximately 80% of the total phenolic
content.
Suppression of the UDP-glucose:sinapate glucosyltransferase leads
to a reduction of sinapine content in the seeds of the GM oilseed
rape plants.
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