Characterizing the nutritional and alkaloid profiles of Tarwi (Lupinus mutabilis Sweet) pods and seeds at different stages of ripening

Tarwi (Lupinus mutabilis Sweet) is a key crop for Andean indigenous communities, offering proteins and fats. Both the pods and seeds of tarwi are consumed, either in their tender (immature) state or as dried, fully ripe seeds. Tarwi, like other Lupinus species, contains high alkaloid levels in its fruits and seeds that must be removed before consumption. This study evaluated the fat, protein, fibre, and alkaloid contents of four cultivars at five maturity stages ranging from 180 to 212 days after sowing. Samples of the pods and the seeds were analysed to determine their colour and protein, crude fibre, fat, and alkaloid contents. The results showed that while the protein concentration in the pods decreased as the fruits matured, the protein content in the seeds increased, reaching approximately 41%. Moreover, the pods exhibited a significant decrease in alcohol content, with the values dropping below 1% at the senescent (dry) stage for all the cultivars. In contrast, the alkaloid levels in the seeds remained stable from 196 days after sowing in the Guaranguito, Andean, and Ecuadorian cultivars, with concentrations around 4%. The present study showed that as the pods matured, their overall protein content decreased, while their seed protein content increased to around 41%. The alkaloid levels in the pods dropped below 1% in the dry stage, while the seed alkaloid levels remained stable at around 4% in the Guaranguito, Andean, and Ecuadorian cultivars after 196 days. However, in the Peruvian cultivar, the alkaloid content remained constant starting from 188 days after sowing, with concentrations just over 3%. This result suggests that as the pods mature, their alkaloid content decreases, while the alkaloid levels in the seeds stabilise from around 188 to 196 days after seeding. Consequently, the alkaloid contents found in the seeds likely originate from other aerial parts of the plant and are not significantly increased by the pods.