Collaborative study of the determination of available lysine in proteins and feeds

In the proposed method 1-fluoro-2,4-dinitrobenzene (DNFB) is reacted with the free epsilon-amino groups in protein of form DNFB-epsilon-amino lysine which is stable to acid hydrolysis. The sample is acid hydrolyzed and unavailable lysine is determined with an amino acid analyzer; total lysine is determined on the untreated sample. The available lysine, which was bound by DNFB, is determined by difference. The available lysine has been determined in 3 samples of 44% protein soybean meal by 5 collaborators, following the method outlined. The range for available lysine in reference standard 1 was 2.02-2.14%, in reference standard 2, 2.59-2.73% and in reference standard 3, 0.55-0.91%. The method has been adopted as official first action.