Determination of Nitrate Ion in Cheese and Sake

The Japanese official analysis method for determination of nitrate ions in food products used as food additives is associated with various challenges. In some kinds of cheese, the extract becomes suspended. The volume of extracted solution is often not accurate owing to the presence of residues in the solution. Moreover, the determination with liquid chromatography-ultraviolet detection (HPLC-UV) is difficult owing to the influence of impurities. Sake usually does not contain lipids or proteins ; therefore, its analysis can be simplified by omitting the co-precipitation steps to remove them. In the present study, for cheese, the amount of sodium hydroxide solution that causes suspension was reduced, and the influence of residues was removed by adjusting the volume after suction filtration. Whereas, sake was diluted with water and centrifuged. Furthermore, solid-phase extraction (SPE) method using cartridge containing carbon molecular sieve to remove the influence of impurities on the chromatogram was successfully established. The recoveries of the nitrate ions were good outcomes of 91.3-99.6% (CV 0.9-4.5%) (n=5). The analysis range was 0.010-0.20 g/kg for cheese, 0.010-0.20 g/L for milk, and 0.010-0.10 g/kg for sake. The developed analysis methods are considered useful, because various challenges of the official analysis method can be solved and the operation are efficient.