Abstract
In order to investigate the differences of the nutritive value between bovine and human milk proteins, young male rats of Sprague-Dawley strain (body weight of 50-60 g) were fed for 14 days on the diets with the content of 8% proteins which were prepared from human normal milk, human colostrum and bovine milk, respectively. The PER (protein efficiency ratio) values of human normal milk, human colostrum and bovine milk were 4.08, 3.37 and 3.40, respectively.
The PER for human normal milk was the highest of all with significance (p<0.01).
The amino acid mixtures which were simulated to human normal milk or bovine milk protein gave quite the same results as these protein diets.
The concentration of urea in the blood plasma of the rats fed on human normal milk protein was lower than that of bovine milk protein.
From the results of the experiments on the supplement of various amino acids to skim milk, it was shown that the difference of the PER values between human and bovine milk proteins was not derived from the difference of the essential amino acid content but mainly from the difference of the cystine content of each milk.
L-Cystine, when supplemented to bovine milk protein, increased PER and decreased the concentra tion of urea in the blood plasma of rats as compared with those for the milk protein.
The diets having the same content of total cystine as human milk, were prepared by mixing casein and milk serum protein at various ratios, with addition of L-cystine if necessary. There were no significant differences in PER among these diets.
Amino acid composition of casein or milk serum protein were similar in both human and bovine milk.
Then it was concluded that the PER for bovine milk protein can be raised to the same value as human milk protein in the rat by adding cystine and/or bovine milk serum protein.
