Abstract
It has been proved in our laboratory that rats fed ozonated casein that did not contain aromatic amino acid residues besides a very small amount of phenylalanine residues had no significant unfavorable change compared with those fed casein and that ozonated casein supplemented with amino acids lost by ozonolysis has nearly the same biological value as that of casein. But some unusual ninhydrin-positive substances existed in urine of rats fed ozonatd casein. Two of them, β-aspartylurea (major component) and 4-methyl-proline (minor), were identified. It was confirmed that β-aspartylurea was formed during ozonolysis of casein in aq. solution that contained urea to solubilize casein and, therefore, present originally in ozonated casein ingested by rats. The origin of 4-methylproline is still obscure.
