Comparison of sample preparation procedures for colorimetric analysis of nitrite in frankfurters

Three groups of methods for analyzing nitrite in meat are compared. All methods consist of a sequence of steps, grouped according to initial extraction procedures. In Group 1, the sample is treated with borate followed by HgCl2 or Carrez I, and then Carrez II. In Group 2, the sample is diluted with water, heated at 80 degrees C, and analyzed immediately (AOAC) or after addition of either Na2CO3 and FeCl3 or HgCl2. In Group 3, the sample is made alkaline with NH4Cl buffer and then treated with one of the following: activated carbon plus Carrez I and II, alumina cream, or AIK(SO4)2. At each step when the method involved the addition of a chemical, supernates and precipitates (if formed) were analyzed for nitrite by Griess reagent both before and after AOAC digestion. The normally discarded precipitates formed after addition of HgCl2 and Carrez I and II contained bound nitrite that could be detected by AOAC analysis. Except in the AOAC method, HgCl2 improved nitrite analysis. Results by AOAC analysis were 3 to 300% higher than those determined after addition of any chemical or combination of chemicals. Spiked meat samples could not be used in comparing nitrite analysis methods because results were misleading. Acid meat samples, such as fermented sausages, required neutralization before AOAC analysis.