PLASMA-FREE AMINO-ACIDS IN CHILDREN CONSUMING LUPIN PROTEIN WITH AND WITHOUT METHIONINE SUPPLEMENTATION

Plasma free amino acids were measured in the fasting state and 3 and 4 hours postprandially in children after 9 days consumption of diets in which lupin provided all of 6.4–6.7% protein kcal, either with supplementation of 2% (grams/gram protein) DL-methionine (L + Met, n = 9) or with an isonitrogenous amount of urea (L + U, n = 10). Fasting concentration of total amino acids (TAA) and of essential amino acids (TEAA) and the TEAA:TAA molar ratio did not differ between diets. Fasting Met concentration (15 ± 4 µmol/liter) and the Met:TEAA ratio (0.021 ± 0.005) were markedly depressed after 9 days of L + U. Supplementation with Met caused an expected increase of Met concentration (25 ± 6 µmol/liter) and the Met:TEAA molar ratio (0.039 ± 0.007) and a profound decrease of Thr concentration (119 ± 28 to 77 ± 22 µmol/liter) and Thr:TEAA (0.165 ± 0.027 to 0.124 ± 0.028). Postprandially after L + U, Met and Met:TEAA did not change from their low fasting values. After L + Met, Met and Met:TEAA increased significantly relative to fasting values. Threonine concentration increased but the Thr:TEAA ratio decreased significantly (0.124 ± 0.028 to 0.111 ± 0.027). These studies confirm Met as the first-limiting amino acid in lupin protein and suggest that Thr becomes limiting when Met is provided in adequate amounts.