COMPARISON OF CHEMICAL METHODS FOR DETERMINATION OF AVAILABLE LYSINE IN VARIOUS PROTEINS

The processing of foods and feeds has a direct effect on the nutritive value of the protein and the biological availability of the amino acids, especially lysine. The available lysine in bovine serum albumin, glandless cottonseed meal, solvent extracted cottonseed meal, gossypol complexed bovine serum albumin, and glanded cottonseed meal and glandless cottonseed meal was determined by the dinitrofluorobenzene (DNFB), sodium borohydride (NaBH4), Carpenter and trinitrobenzenesulfonic acid (TNBS) methods. The DNFB and NaBH4 methods form an acid-resistant bond between the .epsilon.-amino groups of lysine and the blocking compound is formed so that this lysine is not released to acid hydrolysis. The unavailable lysine was determined after hydrolysis with the Beckman amino acid analyzer. The DNFB, NaBH4 and Carpenter methods produced consistent comparable available lysine values in proteins for bovine serum albumin. Available lysine values for cottonseed meals were significantly lower when determined by the Carpenter method. Available lysine values obtained with the TNBS method were consistently lower than those obtained by the other 3 methods.