Effect of Steeping Temperature and Seed Moisture Content on the Quinolizidine Alkaloids in Lupin Seeds

Legumes are essential global sources of plant-based protein, with lupin (Lupinus) species offering exceptionally high protein and fat contents alongside resistance to environmental stresses. However, the presence of toxic and bitter quinolizidine alkaloids restricts the direct consumption of sweet and bitter lupin cultivars. This study evaluated the influence of different steeping regimes, specifically the water temperature (12 °C, 15 °C, or 18 °C) and the target seed moisture degree (40%, 50%, or 60%), on the alkaloid concentration across nine varieties from three lupin species (Lupinus albus, L. angustifolius, and L. luteus). Three main alkaloids were identified and quantified (lupanine, angustifoline and sparteine) in the analyzed samples. Steeping conducted at 18 °C to 60% water content yielded the highest alkaloid reduction (up to 17.57% total loss). A principal component analysis (PCA) revealed that the first two principal components captured 90.90% of the total variance, indicating that the overall alkaloid concentration is overwhelmingly governed by genetic variation (variety) rather than the steeping parameters alone. While low-temperature steeping alone was insufficient to lower the alkaloid content of raw seeds below safety thresholds (<200 mg/kg), steeping at 18 °C to 60% moisture represents a low-energy, viable primary debittering step that preserves seed viability for subsequent germination procedures.