A universal method for Milk Protein by Kjeldahl
With a target to optimise the range of variation in Kjeldahl protein analysis of milk according to official methods like AOAC 991.20 or ISO 8968-1:2001, digestion conditions were varied to obtain lowest variation in protein content between duplicates with the highest possible recovery.
It has been found that digesting for 2 hours at 390°C with a KJELDATHERM digestion block achieves this. Variation in the results across a series of 20 samples was significantly lower than 0.038% protein.The only difference found compared to the official methods was the status of the sample after digestion. Although the official methods require a clear solution it was found not to be necessary in achieving the best results.
All recoveries were checked with Tryptophan achieving a recovery of >99%.