[Effect of processing and amino acids supplementation on the protein quality of amaranth (Amaranthus caudatus)].

The present study was undertaken to evaluate the effect of thermic processing on the protein quality of amaranth (A. caudatus). It was also intended to establish the order of essential amino acid deficiencies suggested by the chemical score as limiting protein quality. The A. caudatus grain was cooked in water in the autoclave at 15 lb pressure during 0, 10, 20, 30, 40, 50 and 60 min. Once cooked, the samples were dehydrated with hot air at 60 degrees C and ground into flours. These were analyzed for: tannins, trypsin inhibitors, hemagglutinins (with cow, sheep, and human erythrocytes), damaged starch, available lysine, protein quality (by the NPR method), and true digestibility. Results indicated that the flours (0 to 60 min cooked) did not contain trypsin inhibitors and that their small tannin content, expressed as catechin, disappeared after 30 min of cooking. The quantities of these antiphysiological substances in the raw material are so small that they do not constitute a factor that may cause a decrease of the product's quality. A positive response was obtained for hemagglutinins, stronger with human erythrocytes, which disappeared with cow's and sheep's erythrocytes after 10 min of cooking and with human erythrocytes, after 20 min. As expected, cooking time increased the damaged starch and a slight increase was observed in available lysine, a finding which was impossible to explain satisfactorily. There were no important changes in true protein digestibility with respect to cooking time. Once again, results demonstrated the positive effect thermic treatment had on protein quality, suggesting the presence of antiphysiological active substances or a low nutrient bioavailability in raw samples. Longer cooking times did not alter substantially the protein quality (NPR and digestibility) and it was concluded that 10 min of cooking is an adequate time for the type of processing used. A sample of processed A. caudatus was utilized for the supplementation studies carried out with threonine, methionine, leucine, individually, or with the three amino acids together at 8.0, 9.5 and 1.0% protein in the diet. According to the results obtained, higher NPR values were observed with 9.0 and 9.5% protein content in the diet. No clear effects were detected when the amino acids were added, but there was an interaction between protein in the diet and amino acids. No effect occurred when leucine was added, suggesting that it is not a limiting amino acid. Possibly, threonine is a more limiting amino acid, but the effects were not as high, probably due to the level added to the diets.(ABSTRACT TRUNCATED AT 400 WORDS)