Protein fractions and their amino acid composition of pseudocereals related to nitrogen supply

摘要

The aim of this study was to investigate the effect of nitrogen (N) supply on seed protein fractions and their ammo acid composition in amaranth (Amaranthus spp.) and quinoa (Chenopodium quinoa Willd). The experiment was carried out at the Institute for Agricultural Chemistry, Georg-August University Goettingen in 2001 and 2002. Two varieties of amaranth and quinoa were treated with three N levels (0, 80 and 120 kg N ha~(-1)). Protein was extracted and separated into five fractions as follows: albumin-1 (ALBU-1), albumin-2 (ALBU-2), globulin (GLOB), glutelin (GLUT) and the insoluble fraction (prolamin and non-protein N compounds). At the higher rates of N supply, lower concentrations of ALBU-1 fractions were found (20.56% and 30.84%, respectively). In ALBU-1 fractions, increased fertilizer rate reduced the histidine (His) content about 16.9% to 18.3% and caused decreased essential amino acid (EAA) content (about 2.9% for each treatment). The N supply did not affect the amino acid composition of the ALBU-2 fractions. In GLOB fractions, the content of methionine (Met) was decreased about 28.1% and 30.9% while phenylalanine (Phe) was increased about 11.6% and 18.4%. In the GLUT fractions, N treatment increased glutamic acid (Glu) and arginine (Arg) contents and decreased threonine (Thr), alanine (Ala), tyrosine (Tyr), valine (Val), lysine (Lys) and leucine (Leu) contents in the seeds. However, the sum of all EAA contents in the seed proteins was not changed. It was concluded that N rates affected the protein fractions and their amino acid composition in the investigated pseudocereals. Increased rates of N decreased Lys and increased Arg in the seeds, whereas the protein and EAA contents in ALBU-1 fractions, which belong to the non-storage proteins, were reduced.