Masaharu Kamei

Improvement of Sample Solution Preparation Method for Nitrite Determination in Foods

The standard method for nitrite assay in foods employs zinc acetate to remove proteins and lipids co-present in the alkaline sample solution. However, the sample solution occasionally becomes muddy, making it hard to determine nitrite by colorimetric analysis. We investigated the elimination of the muddiness by alteration of the concentration ratio of NaOH to zinc acetate in the sample solution. When the final concentrations of NaOH and zinc acetate in the sample solution were 0.05M and 0.9%, respectively, the extracted solutions were clear and appropriate recovery rates were consistently obtained. Briefly, the sample (2.5-5 g) was homogenized with 20 ml of 0.125M NaOH at 80oC in a vessel and moved to a 100 ml volumetric flask. The vessel and the homogenizer were rinsed with 20 ml of fresh NaOH solution and then rinsed five times with 5 ml of hot water. The rinsed solutions were added to the flask each time. Finally, 10 ml of 9% zinc acetate was added to the flask and the contents shaken. The subsequent procedures including heat treatment and the colorimetric process were the same as for the standard method.