Enzymatic hydrolysis of kaempferol 3-O-(2‴-O-sinapoyl-β-sophoroside), the key bitter compound of rapeseed (Brassica napus L.) protein isolate

BACKGROUND: The use of rapeseed protein for human nutrition is primarily limited by its strong bitterness, which is why the key bitter compound, kaempferol 3-O-(2‴-O-sinapoyl-β-sophoroside), is enzymatically degraded. RESULTS: Mass spectrometry analyses of an extract from an untreated rapeseed protein isolate gave three signals for m/z 815 [M-H]. The predominant compound among the three compounds was confirmed as kaempferol-3-O-(2‴-O-sinapoyl-β-sophoroside). Enzymatic hydrolysis of this key bitter compound was achieved using a sinapyl ester cleaving side activity of a ferulic acid esterase (FAE) from the basidiomycete Schizophyllum commune (ScoFAE). Recombinant ferulic acid esterases from Streptomyces werraensis (SwFAE) and from Pleurotus eryngii (PeFAE) possessed better cleavage activity towards methyl sinapate but did not hydrolyze the sinapyl ester linkage of the bitter kaempferol sophoroside. CONCLUSION: Kaempferol-3-O-(2‴-O-sinapoyl-β-sophoroside) was successfully degraded by enzymatic treatment with ScoFAE, which may provide a means to move the status of rapeseed protein from feed additive to food ingredient.