Comparison of Methods for Lysine Screening in Barley

Abstract

Two more rapid colorimetric procedures for crude protein were compared with amino acid analyses of lysine on an amino acid analyzer. The methods were found to be useful and inexpensive compared with amino acid analyses for segregating high-lysine selections of barley (Hordeum sp.). UDY absorbance, which is related to the dye-binding capacity of basic amino acids, was highly correlated with lysine when expressed as milligrams of lysine per 100 mg of ground sample (r = −0.919). When lysine was expressed as grams of lysine per 100 g of protein, the correlation coefficient was −0.479. Low UDY absorbance (i.e., high dye-binding capacity) can be obtained from higher lysine level or higher protein content. Therefore, for more accurate analyses, a Kjeldahl determination should be performed on the samples. A highly significant correlation (r = 0.753) was observed for ninhydrin absorbance of aqueous extracts when compared with lysine analyses. Application of this method is based on the assumption that high-lysine proteins are in the water-soluble protein fractions. Since high ninhydrin absorbance may be produced by increased soluble protein containing normal levels of lysine, the lysine content of samples screened by this method should be verified by amino acid analyses.