Effect of nitrogen fertilizer on nitrogen assimilation and seed quality of amaranth and quinoa

Abstract

Amaranth and quinoa are protein-rich pseudocereals and may be used as an alternative source for non-allergenic food products. Seed composition of amaranth (Amaranthus spp.) and quinoa (Chenopodium quinoa Willd) varieties produced under Northern Germany conditions in 2001 and 2002 was investigated. Amaranth and quinoa seeds contained high protein contents. Their amino acid content was accepted as sufficient for the human nutritional requirements. The proteins were especially rich in lysine. The insoluble dietary fiber was the main part of the dietary fiber content in the seed. Amaranth flour had more pasting viscosity than wheat flour. The effects of nitrogen fertilizer on nitrogen assimilation and seed composition of amaranth and quinoa plants were determined. Nitrogen fertilizer application affected the increase of the grain weight, biomass, grain yield and harvest index. Nitrogen use efficiency, nitrogen utilization efficiency, nitrogen harvest index and grain yield per unit of grain nitrogen decreased with increased nitrogen fertilizer rates. Nitrogen fertilizer application affected the increase of seed protein and linoleic acid content but decreased albumin-1 fractions. The concentrations of essential amino acids were not affected by nitrogen fertilizer application. Albumin-1 fractions had high lysine content, while albumin-2 fractions had high leucine content. Globulin fractions contained higher concentrations of essential amino acids than the other fractions, but lower content of lysine. Glutelin fractions were well balanced in their essential amino acids with exception of methionine. The dietary fiber content was not changed, whereas an increase of the pasting temperature of flours obtained from amaranth and quinoa seeds was negatively related to the nitrogen supply. The present results showed the high potential of amaranth and quinoa seeds in human diet utilization. Nitrogen fertilizer application could be an advantage to improve the nutritional values by increasing protein content and maintaining concentrations of essential amino acids.