Evaluation of the effect of various nitrogen forms on the Lupinus albus seed protein composition

Abstract

The influence of different nitrogen forms: (N₂), [N₂+(NH₄⁺+NO₃^-)], (NH₄⁺), (NO₃^-), (NH₄⁺+NO₃^-) and (-NH₂) on changes of albumin, globulin, prolamin-glutelin, non-fractioned nitrogen and non-protein nitrogen fractions of the protein seed of alkaloid-low content Lupinus albus L. cv. Butan has been studied. The experiments were performed in a greenhouse on perlite using in all cases the constant P, K, Mg and micronutrients (B, Zn, Mn, Cu, Mo, Fe) fertilization. The control was the treatment without any nitrogen support (Nd). It was clearly shown that nitrogen form has significant effect not only on the seed yield and seed protein content, but also on the composition of protein fractions and on the biological value of lupin protein. The main protein fraction of the seeds from all treatments were albumins (16.73-26.10 mgN/g). Among all the treatments, the highest level of globulin was observed for the seeds of plant growing with the symbiotic nitrogen form (15.26 mgN/g), while the lowest one for the control (Nd) (6.86 mgN/g). Symbiotic nitrogen (N₂) treatment clearly increased the glutelin-prolamin fraction while the addition of mineral nitrogen (NH₄⁺+NO₃^-) decreased this fraction from 8.40 to 4.48 mgN/g. The lowest level of the glutelin-prolamin fraction was in the absence of any nitrogen (Nd). Non-protein fraction (Nnp) was highest in the case of plants treated with (-NH₂) (9.92 mgN/g), and the lowest in the absence of nitrogen (Nd) (4.90 mgN/g). The level of non-fractioned nitrogen (Nr), with exception of [N₂+(NH₄⁺+NO₃^-)] and -NH₂ treatments, was closest to the start material. The protein fractions (albumins, globulins and glutelins and prolamins) were also electrophoretically characterized. These analysis confirmed the changes in protein composition of particular fractions under the effect of various nitrogen forms used as a fertilizer.