The Urea/Ammonia Assay Kit (Rapid) will work for measuring urea and ammonia in cheese samples assuming that the levels of these analytes are above the limit of detection for the kit assay.
The detection limit is 0.071 mg of ammonia (or 0.1258 mg of urea)/L, which is derived from a minimum absorbance difference of 0.020 with the maximum sample volume of 2.00 mL.
An example sample preparation procedure for cheese samples (samples containing fat) is provided below. The amount of cheese used in the extraction procedure can be modified. This will mainly be dictated by the level of urea and ammonia present in the cheese so may require some experimentation.
Samples containing fat:
Extract such samples with hot water at a temperature above the melting point of the fat, e.g. in a 100 mL volumetric flask at 60°C. Adjust to room temperature and fill the volumetric flask to the mark with distilled water. Store on ice or in a refrigerator for 15-30 min and then filter through Whatman No. 1 filter paper or centrifuge at 1500 x g for 10 min. Discard the first few mL of filtrate and use the clear filtrate or supernatant (which may be slightly opalescent) for the assay.