Protein distribution in lupin protein isolates from Lupinus angustifolius L. prepared by various isolation techniques

Isabel S. Muranyi, Daniela Volke, Ralf Hoffmann, Peter Eisner, Thomas Herfellner, Markus Brunnbauer, Peter Koehler, Ute Schweiggert-Weisz

Fraunhofer Institute for Process Engineering and Packaging (IVV), Giggenhauser Strasse 35, D-85354 Freising, Germany.

Abstract

Differences in the protein distribution of various protein isolates from Lupinus angustifolius L. Vitabor were identified as affected by the isolation procedure (alkaline and/or salt-induced extraction followed by isoelectric and/or dilutive precipitation). Protein isolates extracted in alkaline solution showed higher protein yields (26.4–31.7%) compared to salt-induced extraction (19.8–30.0%) or combined alkaline and salt-induced extraction (23.3–25.6%). Chemical variations among the protein isolates especially occurred within the albumins. Protein isolates precipitated isoelectrically showed the highest contents, whereas protein isolates precipitated by dilutive showed the lowest contents of conglutin δ. Furthermore, the alkaline subunits of conglutin α and conglutin γ decreased during alkaline extraction compared to salt-induced extraction. A decrease in protein-bound polar and basic amino acids was shown after protein isolation. In contrast, the amounts of nonpolar, aliphatic, aromatic, hydroxylated and sulfur-rich amino acids were higher in the lupin protein isolates compared to the lupin flakes. However, the functional side chains could not be related to the specific molecular arrangements of the protein isolates, as a similar amino acid composition was found among the protein isolates.

Keywords: Lupinus angustifolius L.; Protein yield; Molecular weight; Sodium dodecyl sulfate-polyacrylamide gel electrophoresis; Conglutin; Albumin.