Variation of the amino acid scores and of the nitrogen-to-protein conversion factors in barley grain as a function of nitrogen content as compared with wheat and rye.

Barley grains (9 samples from 7 cultivars) with nitrogen contents (N) ranging from 1.45 to 4.01% of dry matter were analysed for their amino acid (AA) composition with high accuracy from six different hydrolysates per sample. AA levels in grain increased as linear functions of N with correlation coefficients close to unity. A comparison with literature data confirmed that the AA composition of any grain sample of normal barley can be predicted from its N for all phenotypes and genotypes. AAs in grain protein changed as hyperbolic functions of N which increased for Phe, Pro and Glx but more or less strongly decreased for the other AAs. By plotting AA scores against N, barley proteins were shown to be always richer than wheat and rye in Val and Phe + Tyr; sometimes richer than both other species for N less than 2 (Lys); 2.2 (Leu and Ile); 3.4 (Thr); sometimes intermediate to wheat and rye above the latter N values. They were also intermediate in sulphur AAs for N less than 1.9 and drastically poorer for N greater than 1.9. However, they were richer than both other species in Trp for N greater than 1.6. The hyperbolic variations of non-protein nitrogen and nitrogen-to-protein conversion factors were determined as a function of N and also compared with those of wheat and rye.