Plasma amino acid response to single test meals in humans. VI. Determination of available lysine.

The plasma amino acid response to single test meals in young adults was used to determine the amount of physiologically available lysine in heat-treated milk samples. The plasma amino acid responses were evaluated as PAA ratios according to a modified calculation procedure based on the method proposed by Longenecker and Hause. The amount of available lysine was determined by two separate series of single-meal tests. In the first, a relationship was established between the plasma amino acid response (PAA ratio) and the dietary level of lysine (given as synthetic amino acid mixtures). This relationship could be described by linear regression (r = 0.90). This regression line was then used to quantitatively evaluate the lysine PAA ratios obtained from single test meals with heat-treated milk samples. The heat-treatment of the milk samples caused a marked reduction of the amount of physiologically available lysine. The quantitative estimates obtained by the present plasma amino acid technique were in good agreement with determinations of available lysine in the same milk samples based on rat bioassay and chemical analysis.

Plasma amino acid response to single test meals in humans. IV. Four low-cost protein supplements evaluated by chemical analysis, rat bioassay and plasma amino acid response.

For supplementary weaning foods, Faffa (Ethiopia), Incaparina (Guatemala), Superamin (Egypt) and Sekmama (Turkey), were studied with regard to protein quality. Three different methods for protein quality evaluation were used. 1. Chemical analysis of the essential amino acid content. Amino acid scoring of the results indicated that the sulphur-containing amino acids were limiting in Faffa (77%); lysine, threonine and isoleucine in Incaparina (77--75%); threonine in Superamin (80%) and threonine and the sulphur-containing amino acids in Sekmama (90%). 2. Standardized nitrogen balance procedure using laboratory rats. The net protein utilization of the four weaning foods were all in the range 56--70%. Methionine supplementation (1 g/100 g protein) did not significantly improve the biological value of the test diets, but resulted in marked decreased levels of blood urea nitrogen (except for Incaparina), and decreased urinary excretion of urea nitrogen compared to total nitrogen excretion (except for Superamin). 3. Single meal plasma amino acid responses in healthy young adults. The responses of the essential amino acids after test meals with the four weaning foods were all within a range considered to indicate a well balanced supply of dietary amino acids, except for marginal deficits of methionine after the Faffa test meals, and isoleucine after the Incaparina test meals.

Plasma amino acid response to single test meals in humans. V. Ethiopian preschool children given lowcost protein supplements.

The plasma amino acid response to single test meals was studied in preschool children, aged 9 months--5 years. The amount of protein given in each test meal was 1 g per kg body weight, which represented one-third of the daily intake of the children who were recovering from protein-energy malnutrition. The test meals given was gruels made from wheat mixed with a supplementary weaning food (Faffa or Superamin) or fish protein concentrate (FPC). The plasma amino acid responses were evaluated both as PAA ratios (a modification of the Longenecker and Hause method), and as deltaMR% (percentage change in the postprandial essential amino acid molar ratios according to Graham and Placko). Both evaluation models indicated that lysine, threonine and methionine were the limiting amino acids in the Faffa/wheat diet, and that lysine and threonine were limiting in the Superamin/wheat diet. All essential amino acids seemed to be supplied in adequate amounts in the FPC/wheat diet. These results were in close agreement with the amino acid score of the diets (based on chemical analysis).

Plasma amino acid response to single test meals in humans. III. Supplementary effect of dried skim milk and L-methionine on a vegetable protein mixture.

The plasma amino acid response to single test meals in young adults was used for human biological evaluation of the supplementary effect of dried skim milk powder (DSM) and synthetic L-methionine on a vegetable protein mixture. The protein sources in the vegetable mixture were wheat flour, defatted soya bean flour and pea flour. The plasma amino acid responses were evaluated both as PAA ratios (a modification of the Longenecker and Hause method), and as delta MR% (percentage change in the postprandial essential amino acid molar ratios according to Graham and Placko). Both evaluation methods indicated that there was an adequate supply of all the essential amino acids in the basic vegetable mixture, except for a small deficit of methionine. Supplementation (5% and 10%) with DSM did not significantly improve the low plasma amino acid response of methionine. The addition of synthetic L-methionine proved to be very effective in this respect. 1 g of L-methionine per 100 g of proteins from the vegetable mixture gave a plasma methionine response similar to that of the other essential amino acids. This implies that the deficit of methionine in the basic wheat/soya bean/pea mixture was about 30%.

Plasma amino acid response to single test meals in humans. II. Healthy young adults given synthetic amino acid mixtures.

The postprandial plasma amino acid response to test meals containing different amino acid mixtures was analysed in six young adults. The amount of amino acids given in each test meal was equivalent with 3.5 g of nitrogen. Each test meal also contained a large amount of carbohydrate (mainly as wheat starch). Five different amino acid mixtures were used, and the effects on the plasma amino acid response of different dietary levels of lysine, isoleucine and methionine were studied in detail. The plasma amino acid responses were evaluated both by a modified Longenecker and Hause procedure (PAA ratios) and by the procedure proposed by Graham and Placko (percentage changes in the postprandial essential amino acid molar ratios). The plasma amino acid response of lysine was found to be less sensitive to reductions in the dietary supply than the isoleucine and methionine responses evaluated by these procedures. The influence of altered levels of dietary supply on the postprandial plasma concentrations of isoleucine and methionine seemed to be specifically great at the intake levels where these essential amino acids become limiting for protein utilization according to the amino acid score of the test mixtures. The nutritional significance of the postprandial pattern and level of essential amino acids is discussed on basis of the present results. Experimental conditions and evaluation models are examined with regard to the use of single-meal plasma amino acid responses to assess the protein quality of human diets.