Protein quality and digestibility of new high-lysine barley varieties in growing rats

Four new high-lysine barley mutants, the variety Lysimax, with the high-lysine genelys3a and the mutants mother variety Sultan were grown in a field trial in 1993 at Risø, Denmark. Mutants 609, 1242, 1385 and 1405 yielded in the range of 89 to 98 percent and cv Lysimax yielded 102 percent of cv Sultan (100 percent). One-thousand kernel weights for the mutants were in the range of 87 to 97 percent and cv Lysimax 83 percent of cv Sultan (100 percent). Protein contents of the mutants were slightly higher, in the range of 13.2 to 13.6 percent, than of cv Sultan (13.1 percent) and Lysimax which had a protein content of 12.6 percent. Fat content was higher in Lysimax and in the mutants except for mutant 1385 than in cv Sultan while dietary fibre contents of the barleys were similar. The levels of -glucans and starch were usually lower in Lysimax and in the mutants. The highest lysine levels: 4.6, 4.0 and 3.7 g/16 g N occurred in cv Lysimax and mutants 609 and 1405 compared to 3.3, 3.3 and 3.2 for cv Sultan and mutants 1242 and 1385, respectively. Mutants 609 and 1405 and cv Lysimax also had higher levels of threonine, histidine and valine. The increased lysine contents resulted in large, at most 20 percent, increases in biological value; 88.8, 81.7 and 78.3 percent for cv Lysimax and mutants 609 and 1405 compared to 74.2 percent for cv Sultan. True protein digestibilities and energy digestibilities were slightly lower in Lysimax than in Sultan, 5.3 and 4.3 percentage units, respectively. It is concluded that the development of high-lysine barley varieties is very beneficial for meeting the requirements of indispensable amino acids for humans and monogastric animals. In addition, nitrogen excretion into the environment is drastically reduced due to the higher biological values of the mutants.