Studies on the Composition and Nutritive Value of Forage Grass by Means of Structural Analysis

V. Biological Values for Rats of Protein Obtained from the Concentrated Parts of Red Clover and Kentucky 31 Fescue with or without Supplement of Some Deficient Amino Acids

Abstract

Experiments were performed to know whether some essential amino acids were deficient in grass protein and whether the addition of such dificient amino acids to grass protein was able to increase the biological value of proteins for rats.
The concentrated parts of red clover (RC) and Kentuchy 31 fescue (KF) was prepared by the structural analysis method described in the previous paper (1959). The concentrated part contained 46.7 and 27.8 per cent crude protein on the basis of air-dried matter in RC and KF, respectively.
In this experiment, amino-acid analysis was first made chemically by applying column chromatography. Then deficient amino acids were searched for indirectly by measuring twice the biological value of protein.
The method of MOORE and STEIN (1951) was employed for amino-acid analysis. It was found that RC and KF were almost the same in the amino-acid composition of the concentrated part, which was as follows: serine 4.24 (4.21), glutamic acid 12.99 (11.15), glycine 5.70 (6.08), alanine 6.24 (6.75), valine 6.50 (6.75), methionine 1.10 (1.19), isoleucine 5.78 (5.34), leucine 10.94 (9.04), tyrosine 4.19 (3.51), phenylalanine 7.06 (6.44), tryptophan 1.49 (1.31), histidine 2.47 (2.44), arginine 6.15 (5.86), and lysine 6.34 (5.53) in RC and in KF (shown in parentheses) when expressed in grams per 16g of nitrogen. In this composition, aspartic acid and threonine were determined together as a single substance in the protein of RC, because they could not be separated in this analysis. As a result, glutamic acid and the peak which contained aspartic acid and threonine were found to be the highest and leucine was the second highest. Methionine was the lowest amino-acid content. Trytophan, histidine, and tyrosine were found to be the second lowest contents.
To measure the biological value of protein for rats, a diet containing a 10% level of protein was used. The results of determination of the amino-acid contents of the concentrated part in RC and KF were compared with the amino-acid requirements for young rats presented by ROSE (1937). It was proved that four amino acids, methionine, lysine histidine, and tryptophan (with threonine only in the case of KF), were more or less, deficient in these diets. Then trials were carrid out to examine the following five different diets for biological value and digestibility: (1) diet containing the concentrated part (CP) of RC as the sole protein source, (2) that containing the CP of KF as the sole protein source, (3) that containing the CP of RC supplemented with such amino acids as DL-methionine, L-lysine-HCl, and Lhistidine-HCl-H₂O, (4) that containing the CP of KF supplemented with such amino acids as mentioned above and DL-threonine, and (5) that containing casein supplemented with DL-methionine and L-lysine-HCl. Diet No. 5 served as control.
The results obtained showed that neither RC protein nor KF protein had any high biological value, which was as low as 29 and 44, respectively. When essential amino acids were supplemented to RC and KF proteins, the biological value of each grass was increased remarkably, reaching 97 per cent in RC and 94 per cent in KF. This fact indicates that the grass proteins were deficient in the amino acids added to the diets. The digestibility of grass protein was also found to increase to some extent when the same deficient amino acids were added to the diet. The rate of increase, however, was not so high in the digestibility as in the biological value. Some difference was seen in the increase of digestibility between RC protein and KF protein.