Protein quality and digestibility of sorghum in preschool children: balance studies and plasma free amino acids.

The protein quality and digestibility of two high lysine (2.9-3.0 g/100 g protein) and tow conventional varieties (lysine content 2.1-2.2 g/100 g protein) of whole grain sorghum milled as flour were assessed through balance studies in 13 children 6-30 months of age. Sorghum protein provided 6.4 or 8.0% of dietary energy. Control diets contained 64% kcal protein as casein. Children consumed 100-150 kcal/kg body weight/day. Sorghum consumption was associated with weight loss or poor weight gain. We found no difference by variety in apparent nitrogen absorption or retention. Mean absorption and retention of nitrogen (+/- SD) from 26 six-day sorghum dietary periods were 46 +/- 17% and 14 +/- 10% of intake, respectively (corresponding preceding casein control values: 81 +/- 5% and 38 +/- 3%). Stool weight and energy losses during sorghum periods averaged 2.5 to 3 times control values. Plasma amino acids were determined in eleven children after 16 days of sorghum consumption. Fasting concentration of total amino acids (TAA) was similar to values previously obtained with wheat protein at similar levels of intake. Total concentration of essential amino acids (TEAA) was low as were concentrations of lysine (Lys) and threonine (Thr). Analysis of postprandial changes of the Lys/TEAA and Thr/TEAA molar ratios confirmed that Lys was the first limiting amino acid.