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A simplified procedure for calculating amino-acid scores of blended foods or dietary patterns

G. Richard Jansen and Judson M. Harper
Colorado State University, Fort Collins, Colorado, USA

Amino-acid scores provide a useful estimate of the protein quality of blended foods or dietary patterns and are an acceptable substitute for the biological assays [1]. The most recent international recommendations for an aminoacid reference pattern are given separately for infants and pre-school children [2] . None are given for adults because amino-acid pattern is rarely a factor limiting the utilization of protein in the diets of adults. For persons of all ages, however, the digestibility of the protein must be taken into account. The calculations that follow are for children of two to four years of age and need to be further adjusted for the digestibility of the dietary protein. In the absence of specific data it can be assumed to be 90 per cent or more for mixed blended foods containing animal protein and 80 per cent or more even for diets that are entirely of vegetable origin [3] .

The following procedure has been simplified by including only those amino-acids likely to be found limiting in weaning foods and diets and by providing a standard format for entering the required data and calculating net protein value. Calculation of the protein value of formulas for infants by this procedure would require use of the aminoacid pattern proposed for this age group in the FAO/VVHO/ UNU report. Because it is often difficult to locate data on the aminoacid content likely to be used in weaning food mixtures, values provided by the Agency for International Development are given in table [4].

DIRECTIONS

1. Record on the work sheet (fig. 1 ) the reference number and the weight in grams for each of the components of the mixture.
2. Record the amounts of nitrogen (N), protein, Iysine,
threonine, tryptophan and sulphur amino acids (methionine plus cystine) by multiplying the corresponding handbook values by the weight of the component in grams divided by 100 (see table 1, note a).
3. Add up the weight and amounts of N. Iys, tier, try, and SAA in the total mixture.
4. To obtain mg/gN divide the amounts (mg) of Iys, tier, try, and SAA by the amount (9) of N in the mixture.
5. To obtain amino-acid scores divide the mg/gN for each amino acid by the corresponding values in mg/gN listed for the 1983 FAOtWHO/UNU pattern x 100 [2] .
6. To calculate per cent protein, g protein in mixture should be divided by the weight of mixture (g) x 100.
7. To obtain net protein value (NPV) multiply the lowest amino-acid score by the per cent protein divided by 100.

Figure 1. Sample work sheet

TABLE 1. Amino-acid scores of floodsa

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