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Identification of novel saponins in vegetable amaranth and characterization of their hemolytic activity

Amaranth is a plant genus of global importance comprising more than 60 species that are dually used for human consumption. While the grains are used as pseudo-cereals mainly in America and Asia, leaves are also consumed as leafy vegetable in African countries. Besides further secondary plant metabolites, saponins are described as major bioactive constituents in amaranth species. These triterpenoid saponins belonging to the oleanane-type are assumed to be part of the plant defense system and are often also associated with potential health risks for the consumer, mainly due to hemolytic properties. However, data concerning amaranth saponins are limited to the grains of single cultivars of only a few species investigated.

The aim of the present work was to determine the saponin profile in leaves of various amaranth cultivars grown under identical conditions. Out of 15 cultivars, six did not show any indications for the presence of saponins in HPLC–MS analysis. Two saponin-rich cultivars (one of Amaraanthus hybridus and one of Amaranthus hypochondriacus) as well as commercially available amaranth grains were selected for an in-depth analysis using a combined approach of high resolution and multi stage mass spectrometry. Three previously undescribed monodesmosidic and four bidesmosidic saponins could be assigned according to the MS data. Four novel saponins were also found in commercial grain amaranth analyzed for comparison. The investigation of the hemolytic effects revealed that only one saponin exerts significant activity whilst the further saponins did not lyse erythrocytes in vitro.

The results show that the saponin profile of amaranth cultivars is more diverse than reported so far. However, the biological activity seems to be different for the single structures. Thus, a more comprehensive case-by-case investigation of amaranth saponins is required to evaluate the impact of these secondary metabolites on humans and plants.

Zehring, J.; Reim, V.; Schröter, D.; Neugart, S.; Schreiner, M.; Rohn, S.; Maul, R. 2015. Identification of novel saponins in vegetable amaranth and characterization of their hemolytic activity. Food Research International 78, 361-368.