Alkaloids Derived from Lysine: Quinolizidine Alkaloids, a Focus on Lupin Alkaloids

Quinolizidine alkaloids (QAs) are a group of alkaloids chemically related to quinolizidine ring and are usually known as lupin alkaloids because they mainly occur in lupin species and other plants of the Genisteae tribe. They are secondary metabolites synthesized from lysine by plants, as a part of the defense strategy against pathogens and other predators. QAs are biosynthesized in green tissues of the plant, transported via phloem and stored in all organs of the plant, especially in seeds. QAs content depends on genotype, plant organ, presence of pathogens, and pedo-climatic conditions such as environmental effects and soil characteristics. For these reasons, the alkaloid pattern is highly variable among different Lupinus species, with lupanine and sparteine being the most common QAs. QAs show neurotoxicity, and food authorities of some countries have fixed a limit of 200 mg kg−1 of total QAs in seeds and lupin-based products for human nutrition. The level of QAs in lupin seeds can be reduced by debittering processes involving soaking or washing with water. Moreover, some lupin varieties producing low content of QAs were selected and bred.