A simple procedure of lupin seed protein fractionation for selective food applications

A simple procedure aimed at fractionating the main proteins of lupin seeds is proposed. The protocol consisted of alkali extraction of all proteins and isoelectric precipitation of two classical storage globulins, namely conglutins α and β, and one albumin, conglutin δ. The supernatant of this separation contained conglutin γ, the other main lupin protein. Conglutin γ could easily be purified further by selective Zn 2+ precipitation, leading to a more than eightfold enrichment with respect to the amount in the flour. Resuspension of the isoelectric precipitate in saline water/ethanol solution allowed us to isolate conglutin δ, a 2S sulphur-rich lupin protein, at a very high purity level. Conglutins α and β could not be separated further by simple procedures. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis analysis confirmed the identities of the isolated protein fractions. The distribution of each separated protein type is close to that of the corresponding proteins in the seed. The results are discussed in view of the applicability of the method and the potential use of each protein type as a food ingredient.