K. Ranfft et U. Faure, AN INTERCOMPARISON OF METHODS FOR THE DETERMINATION OF TRYPTOPHAN IN FEEDSTUFFS, Agribiological research, 46(1), 1993, pp. 65-72
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.