Amino acids scoring

Feedstuffs consist largely of complex polymers (e.g. proteins, starches, fats) that must be hydrolyzed to the constituent building blocks before they can be absorbed and made available to the host. The digestibility of many plant proteins is inherently lower compared to proteins from animal tissues. This is particularly true for the structural proteins (Carbonaro et al, 2000 Mariotti et al, 1999). As a consequence, amino acid scores for many plant proteins often do not reflect true availability to the host (Mariotti et al, 2001). 

In recent years, a number of workers have published amino acid analyses of the sweet potato (38, 43, 35, 22, 18). The overall picture is that the sweet potato amino acid pattern is of good nutritional quality but that the variability of individual amino acids both within the same cultivar and across cultivars is very high. For example, Walter et al. (44) reported that with the exception of aromatic amino acids, every essential amino acid has a score of less than 100 in one or more cultivars. The amino acid score is defined as the g of amino acid in 100 g of test protein divided by the number of g of that amino acid in the FAO/WHO reference pattern times 100. Bradbury et al. (22) showed that, for the same cultivar, environmental effects on the amino acid patterns is significant. For three cultivars, they found a mean percent standard deviation for all amino acids of 24.2,... 

The literature on concentrated sweet potato protein is sparse. Amino acid patterns for sweet potato protein isolates have been reported by three groups (16, 45, 46). One report showed that when compared to the FAO standard (47), no amino acids were limiting. The other reports showed total sulfur amino acids and lysine to be limiting (Table III). The patterns indicate a nutritionally well balanced protein. The improvement in nutritional quality, when compared to amino acid patterns from whole sweet potato, is due to the fact that whole sweet potatoes contain substantial amounts of NPN, which consists mainly of nonessential amino acids. This effectively dilutes the EAA and lowers the amino acid score. 

Basic Protocol 2 Protein Digestibility-Corrected Amino Acid Score... 

PROTEIN DIGESTIBILITY-CORRECTED AMINO ACID SCORE (PDCAAS) TO DETERMINE PROTEIN QUALITY... 

PDCAAS (%) is calculated as the product of the true protein digestibility and the amino acid score (or lowest amino acid ratio) relative to reference protein. Amino acid composition of protein is determined by hydrolyzing the protein into its component amino acids and then separating the amino acids chromatographically as described below. True protein digestibility is determined according to Alternate Protocol 2. 

Table B2.1.1 An Example Of Calculation For Amino Acid Score Using Whey Protein"...

Calculate the amino acid score from an amino acid profile ... 

See Table B2.1.1 for an example of the calculation for amino acid score using whey protein. 

Correct the amino acid score for protein digestibility by multiplying the lowest amino acid ratio with true protein digestibility (see Alternate Protocol 2). An example ... 

Sarwar, G. 1996. The protein digestibility-corrected amino acid score method overestimates quality of proteins containing andnutritional factors and of poorly digestible proteins supplemented with limiting amino acids in rats. J. Nutr. 127 758-764. 

Young, V.R. and Pellett, P.L. 1991. Protein evaluation, amino acid scoring and the Food and Drug Administration s proposed food labeling regulations. J. Nutr. 121 145-150. 

TABLE 2.3 Amino acid scoring patterns mg/g protein requirements of infants, children, adolescents and adults over 18 (genders combined)°... 

PDCAAS is calculated as true protein digestibility (TD) x Amino Acid Score (AAS) (WHO/FAO/UNU Expert Consultation, 2007). 

Henley, E. C. and Kuster, J. M. (1994). Protein quality evaluation by protein digestibility-corrected amino acid scoring. Food Technol. 48(4), 74-77. 

Recommended dietary allowance of good-quality protein is 0.83 g/kg of body weight per day with the protein digestibility-corrected amino acid score value of 1.0 (WHO, 2002). Acceptable macronutrient distribution... 

In spite of this fact, in most studies, amino acid score (AAS), index of essential amino acid, and egg protein have been applied. Seaweeds have usually low AAS (about 20-67%) nevertheless, it is common similarly to other plants (Matanjim et ah, 2009). Matanjim et al. (2009) showed that Sargassum polycystum had AAS higher (67%) than soybeans (47%) or casein (58%) and then this value could be compared with beef (69%). 

For some time the use of an amino acid score has been advocated as an alternative to the PER. Although clearly the quality of some proteins can be assessed directly by using amino acid score values, but that of others cannot be assessed because of poor digestibility and/or bioavailability. Consequently, both amino acid composition and digestibility measurements are considered necessary to predict accurately the protein quality of foods for human diets [109] (Table 3.17). 

Specifically evaluating the method recommended by the CCVP, i.e., amino acid score corrected for digestibility [116]... 

Methodology for determining the amino acid composition of proteins. The consultation concluded that modem amino acid analysis can provide data with repeatability within a laboratory of about 5% and reproducibility between laboratories of about 10%. It recommended that this variability be considered acceptable for the purposes of calculating the amino acid score. To achieve such results requires careful attention to many aspects of the protocols, including replicating the complete analytical procedure [118]. 

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