Evaluation of protein composition and functionality of lupin protein isolates extracted from different blue lupin (Lupinus angustifolius) cultivars

Lupin is a promising alternative protein source due to the climate resilience of this crop and its large protein content. Protein isolates (PIs) were obtained after alkaline extraction-isoelectric precipitation from 22 narrow-leaf lupin genotypes from commercial and experimental breeding lines cultivated under controlled environmental conditions. The isolates were screened for their protein content and ratio of the main proteins, namely α-conglutin (legumin-like) and β-conglutin (vicilin-like). The molecular mass of the proteins ranged from 320 to 400 kDa and 180-260 kDa for α- and β-conglutins, respectively. In all genotypes, the ratio of α-conglutin to the total (sum of α-conglutin + β-conglutin) exceeded 53 %. Six varieties were selected for further compositional and functional analysis. Protein isolation reduced alkaloids below 200 mg/kg, especially for isolates with higher protein content. Regardless the differences in the conglutins' composition between the protein isolates, all protein isolates showed similar protein solubility, evaluated at a range of pH values. The produced protein isolates presented higher solubility than a commercially available lupin PI due to their milder extraction conditions. The most abundant essential amino acids were leucine and lysine, while the limiting one was methionine. The surface activity of the isolates at oil-water interfaces was evaluated using drop tensiometry, showing no differences with composition. The work clearly demonstrates the potential of PIs from lupin as a nutritionally-valuable ingredient to be safely used in foods.