Effect of aqueous and alkaline thermal treatments on chemical composition and oligosaccharide, alkaloid and tannin contents of Lupinus campestris seeds

The utilisation of Lupinus campestris seeds has been limited for some years owing to the presence of toxic quinolizidine alkaloids (QAs) and antinutritional factors (ANFs). The oligosaccharide content was analysed by high-pressure liquid chromatography (HPLC). Gas chromatography coupled with mass spectrometry (GC/MS) was used to detect alkaloids, using caffeine (0.2 mg ml^-1) as internal standard. Tannins were determined by the Folin-Dennis colorimetric method. Two methods were tested to reduce or eliminate the QAs and ANFs, (a) aqueous thermal treatment and (b) alkaline thermal treatment (NaHCO₃ 0.5% solution), both of them for 6h at boiling temperature. In both cases the removal of oligosaccharides, in amounts of 70 and 90% respectively, was also achieved. The alkaloid contents were reduced to innocuous levels in both cases (less than 0.4-0.5%). The alkaline thermal treatment, in which the seed had a final alkaloid content of 0.002%, was more efficient than the aqueous thermal treatment. The tannin content also showed a reduction of 71% with the aqueous treatment and 77% with the alkaline treatment. The results show that alkaline thermal treatment is more efficient at eliminating these ANFs.