D-amino acids in non-gelling components of gelatin

As a possible cause of the non-gelling property of the sol fraction of gelatin, we considered that higher D-amino acid content should result in decreased formation of helices. The sol fractions were extracted from gelatin gels and hydrolyzed to amino acid mixtures. The rates of reaction with D-amino acid oxidase (D-AOX) were recorded for the hydrolyzates. For a comparison, residual gels were also treated similarly. The sol fractions always gave higher results than the residual gels for the three types of gelatin examined. The result also showed that the rates obtained from the sol fractions were in the order: limed ossein > limed hide > acid pigskin. To examine the reliability of this procedure the D-form content for each amino acid in the sol from the limed hide gelatin mas compared with that of the residual gel. The contents in the sol mere higher than those in the residue for most of the amino acids which racemized. The results indicate that the increased racemization of amino acids on the extraction of gelatin from raze materials is a cause of the non-gelling property.