AN INTERCOMPARISON OF METHODS FOR THE DETERMINATION OF TRYPTOPHAN IN FEEDSTUFFS

An intercomparison of methods for the determination of Tryptophan in f eedstuffs with 14 participants from 8 European countries is described. The study was undertaken by the BCR-Programme (Community Bureau of Re ference) of the Commission of the European Communities as part of a br oad activity to improve accuracy and agreement of measurements of impo rtance in food and agriculture. In Regulation 79/373/CEE, the facultat ive declaration of the Tryptophan content is foreseen. It is therefore planned to develop an Official Community Method for the determination of Tryptophan in feedstuffs and to certify the content of Tryptophan in 4 feed reference materials which have already been prepared for det ermination of amino acids: mixed pig feed (RM 117), low fat fish meal (RM 118), soybean meal (RM 119) and skim milk powder (RM 120). The par ticipating laboratories analyzed 5 materials (corn, soybean meal, fish meal, meat and bone meal without added Tryptophan and a mixed feed wi th added Tryptophan). Information is given on the methods used and the results obtained. Coefficients of variation calculated from the resul ts after elimination of outliers are between 3.9 % and 10 % for sample s without added Tryptophan and 26 % for the added Tryptophan content o f the mixed feed. The study showed that even with use of a range of me thods, results are good for samples without added Tryptophan but the d etermination of added Tryptophan needs further improvement. The interc omparison has allowed definition of a Candidate Official Method which will be studied in a second study.