Equilibrium between basic nitrogen compounds in lupin seeds with differentiated alkaloid content

Abstract

The results of studies on the content of the nitrogen basic compounds, viz. quinolizidine alkaloids, biogenic polyamines and basic amino acids in lupin seeds are presented. The investigations concerned three lupin species ( Lupinus angustifolius L., Lupinus albus L. and Lupinus luteus L.) and 10 bitter and sweet cultivated varieties. Content of quinolizidine alkaloids in L. angustifolius ranged from 11.4 to 19.6 μg mg −1 dw (bitter cultivars), from 0.18 to 0.47 μg mg −1 dw (sweet), in L. albus from 0.58 μg mg −1 dw (sweet) to 29.6 μg mg −1 dw (bitter) and in L. luteus from 0.59 (sweet) to 14.7 μg mg −1 dw (bitter). Total biogenic polyamine content ranged in L. angustifolius from 2773.9 to 3180.2 pmol mg −1 dw (bitter) and from 315.0 to 599.0 pmol mg −1 dw (sweet), in L. albus from 432.6 pmol mg −1 dw (sweet) to 1832.0 pmol mg −1 dw (bitter) and in L. luteus from 506.9 pmol mg −1 dw (sweet) to 2091.8 pmol mg −1 dw (bitter). Total basic amino acids varied in L. angustifolius from 1034.3 to 1704.6 pmol mg −1 dw (bitter) and from 1761.9 to 2101.9 pmol mg −1 dw (sweet), in L. albus from 696.9 pmol mg −1 dw (bitter) to 1269.2 pmol mg −1 dw (sweet) and in L. luteus from 927.6 pmol mg −1 dw (bitter) to 1598.3 pmol mg −1 dw (sweet). We found a close dependence between alkaloid content and level of biogenic polyamines and basic amino acids in all three lupin species tested. All bitter lupin seeds also contain high level of biogenic polyamines but a low content of basic amino acids. The reverse relationship in sweet lupin seeds was found. The findings demonstrate that lupin nitrogen basic compounds are in steady equilibrium and that change of content in one compound leads to corresponding change in the content of another.