The chemical composition and protein quality of amaranth grain germ plasm in Guatemala

The present research was carried out for the purpose of collecting part of the germ plasm of grain amaranth in Guatemala, as well as to evaluate it in terms of yield, chemical composition and nutritive value. A total of 27 Guatemalan selections, one from Mexico and seven from Peru were planted in June 1982 in 7.5 m2 experimental plots replicated four times. The harvest seed was utilized for analysis of protein, ether extract, crude fiber, tannin content and trypsin inhibitors, as well as for NPR assays. A group of five pooled samples was made based on protein content for amino acid analyses; 10 samples were selected for a second NPR and protein digestibility assay. A preliminary assay on amino acid supplementation of raw grain flour is also reported. The selections were significantly different in grain yield. In general, selections which flowered at a short height and were harvested also at short height, tended to yield more seed. Findings revealed a negative relationship between plant height and grain yield, but a positive relationship between plant height and dry vegetable residue. Protein content of the grain averaged 15.0% with values ranging from 12.8 to 17.4%. Fat content varied from 5.6 to 10.6% with an average of 8.4%. Amaranth grain with a higher protein content contained greater amounts of amino acids on a weight basis, but when these were expressed on a nitrogen basis, differences disappeared. Based on the FAO/WHO amino acid reference pattern, grain amaranth protein was deficient in sulfur amino acids. Although the biological trial corroborated this deficiency, more studies should be undertaken. The NPR values of the samples from Peru averaged 2.30, the one from Mexico 2.04 and those from Guatemala, 2.36. Protein digestibility was 80, 82 and 74%, respectively. The data suggest that there is sufficient variability to select materials of a higher chemical composition, nutritive value, and yield.