A comparison of analytical methods for the determination of urea in yeast-based food and feed ingredients.

Urea is a non-protein nitrogen compound, authorised in the EU as a nutritional source of nitrogen in animal feed intended for ruminants with a functional rumen. The Rapid Alert System for Food and Feed (RASFF) is the EU online platform through which food and feed safety risks are reported. During 2017, several rapid alerts were raised in the EU by individual member states regarding the presence of unlabelled urea in feed-grade yeast. The presence of urea in animal feed is analysed with a spectro-colorimetric method, which is the EU official control method. Other urea analytical methods include enzymatic and LC-MS methods, which are also investigated in this study. The main objectives of this study were to analyse yeast feed-grade and food-grade products with independent laboratories using the EU official control method, as well as enzymatic and LC-MS methods. Comparison of results from the spectro-colorimetric, enzymatic and LC-MS methods for reliability, consistency and accuracy determined the most reliable method for the quantification of urea in animal feed. Yeast food and feed samples were tested using four independent laboratories. Results demonstrated a lack of consistency both within the same laboratory and between separate laboratories for urea quantification using the EU official control method. Urea quantification results for the AOAC 941.04 enzymatic method were found to be much higher than anticipated. The LC-MS method yielded the most consistent and reliable results. In conclusion, urea quantification by LC-MS analysis has the potential to be a viable method for urea analysis of yeast samples.