Ammonia test in milk and dairy products

Whole or skimmed milk: use as is. Use the “NH₃ milk” curve.
Cheese: Weight 5 gr of sample, crumble it and mix in 45 mL of distilled water. Centrifuge or filter in order to separate the larger parts. Rapidly process the sample because ammonia tends to increase. Use the “NH₃ cheese” curve.
Fresh cream: Take 4 mL of cream in a centrifuge tube, add 100 uL of HCL (diluted 1:10), shake it and centrifuge for 5 minutes. Take the aqueous solution and filter it, if necessary. Use the “NH₃ milk” curve to test.

The ammonium ions react with a phenolic derivative and form a blue-green colored complex whose intensity, measured at 700 nm, is directly proportional to the concentration of ammonia in the sample.

The Poligny ACTALIA (France) reference laboratory, specialising in food analysis, performed an evaluation study: the determination of ammonia on whey was performed with CDR FoodLab^® and with the enzymatic reference method (NF V 04-217). The correlation between the CDR FoodLab^® method and the reference method was found to be good, considering the type of analysis and the difficulty in performing the reference methodology, obtaining an R² = 0.9265.