Quantitative determination of the protein content of citrus leaf extracts: A comparative study

Three spectrophotometric methods for the quantitative determination of proteins were compared taking as a reference the method of Kjeldahl. The abnormally high protein values obtained when these methods were applied to soluble extracts were decreased by using protective and precipitating agents. The method of M. M. Bradford (Anal. Biochem. 72, 248–254 (1976)) gave values identical to the method of Kjeldahl when ethylenediaminetetracetic acid, 2-mercaptoethanol, and polyvinylpolypyrrolidone were added to the extraction medium and the soluble proteins were precipitated with trichloroacetic acid prior to protein determination.