Hydrolysis conditions for the analysis for sulphur amino acids in feedstuffs

A study of methods of analysis for sulphur amino acids in feeds was undertaken with a view to finding methods suitable for the routine analysis of feedstuffs. In the case of cyst(e)ine, it was found that the results obtained from simple oxidation and hydrolysis with a mixture of dimethylsulphoxide (OMSO) and hydrochloric acid correlated well with those obtained from performic acid oxidation (PAO) and subsequent hydrolysis (r = 0,94). It was also found that evacuation was not necessary in the OMSO-HCI oxidationhydrolysis procedure. Added cyst(e)ine could not be recovered quantitatively; 82% being recovered from a blank hydrolysis, 73% when starch and tryptophan were also present and only 50% when added to a mixed feed. Methionine, measured after a normal evacuated hydrolysis, did not correlate well with methionine recovered as methionine sui phone after PAO (r = 0,79). However, over 90% of methionine added to a complete feed could be recovered after the normal evacuated hydrolysis.