Determination of Total Protein Content in Gelatin Solutions with the Lowry or Biuret Assay



ABSTRACT:  Gelatins can be obtained from different sources and prepared using different processes, and the end product gelatin may vary in amino acid composition and molecular weight distribution. In the present study, the variation in “protein color” development among gelatins in colorimetric total protein content measurements was investigated at 540 nm using the Biuret assay and at 650 nm using the Lowry assay, with bovine serum albumin as the reference protein. In both the Biuret and Lowry assays, the color response varied significantly among gelatins. The difference in imino acid content was the major factor responsible for this variation, which probably influenced the gelatin helix → coil phase transition and resulted in the difference in gelatin associate state. Based on their “protein color” development abilities in both Biuret and Lowry, gelatins were classified into 2 major groups with the hierarchical cluster analysis: 1 group included all cold water fish gelatins, while the other included gelatins from warm water fish, avian, and mammalian species.