I. Overview
Nitrite is used as a coloring agent in meat products in a limited amount, making meat products look red and beautiful, but humans ingesting 0.3 to 0.5 grams of nitrite can cause poisoning or even death. The chance of food poisoning caused by nitrite is high, and poisoning events often occur.
The detection of nitrite in meat enema can be performed by ion chromatography and spectrophotometry. This paper mainly describes the spectrophotometry.
Second, the program introduction
1 , measurement standards and methods
GB 5009.33-2016, spectrophotometry
2 , the required instruments and reagents
722S visible spectrophotometer, one tenth electronic balance, electric furnace, water bath, common glass instruments, etc.
Saturated borax solution, potassium ferrocyanide solution, zinc acetate solution, sodium nitrite standard use solution, aminobenzenesulfonic acid solution, naphthylethylenediamine hydrochloride solution, and the like.
3 , the experimental steps
After precipitating protein and removing fat, the sample is diazotized with p-aminobenzenesulfonic acid under weak acid conditions, and then coupled with naphthylethylenediamine hydrochloride to form a purple-red dye. The nitrite content is determined by external standard method. . details as follows:
(1) Preparation
Use a beaker to hold water and use an electric stove to heat to boiling, and reserve (to prepare water of about 70 degrees);
Turn on the power in the water bath to let the water boil and reserve.
Remove the meat enema and cut it, and use a balance to weigh 5g of the sample into a 500 mL volumetric flask, add 12.5 mL of saturated borax solution, stir evenly, add about 300 mL of water at 70 °C, in a boiling water bath. Heat for 15 min, remove and cool in a cold water bath, and set to room temperature.
(2) Extraction and purification
Add 5 mL of potassium ferrocyanide solution to the vial, shake well, add 5 mL of zinc acetate solution, mix and shake the extract, add water to the mark, shake well, place for 30 min, remove the upper layer of fat, supernatant Filter with filter paper, discard 30 mL of the initial filtrate, and leave the filtrate for use.
(3) Sample determination
Pipette 40.0 mL of the above filtrate into a 50 mL plugged colorimetric tube, and draw 0.00 mL, 0.20 mL, 0.40 mL, 0.60 mL, 0.80 mL, 1.00 mL, 1.50 mL, 2.00 mL, 2.50 mL of sodium nitrite standard solution ( Equivalent to 0.0 μg, 1.0 μg, 2.0 μg, 3.0 μg, 4.0 μg, 5.0 μg, 7.5 μg, 10.0 μg, 12.5 μg sodium nitrite) in a 50 mL plug-in colorimetric tube.
Add 2 mL of p-aminobenzenesulfonic acid solution to the standard tube and the sample tube, mix well, and let stand for 3 min to 5 min, then add 1 mL of naphthylethylenediamine hydrochloride solution, add water to the mark, mix, and let stand. For 15 min, use a 2 cm cuvette to adjust the zero point with a zero tube, measure the absorbance at a wavelength of 538 nm, and compare the standard curve. At the same time do reagent blanks.
4 , calculation formula and results
According to the standard curve, enter the absorbance to determine the concentration A (ug), and then calculate the nitrite content mg/kg in the meat enema according to the following formula, and calculate the average content in the sample by calculation.
The national limit value is 30 mg/kg. If the calculated result is greater than 30 mg/kg, the nitrite in the sample exceeds the standard. The recoveries of spectrophotometry were over 98.5%.
Third, summary
When buying meat sausages, it is best to buy them carefully for brightly colored and particularly good-looking meat products.
However, sausage bacon does not necessarily exceed nitrite. In meat processing, nitrite is allowed to be used within the legal scope and at a safe dose to prevent the growth of pathogenic microorganisms and maintain the color of the meat, which will be beneficial to the preservation of meat. And transportation.
For example, we often eat ham, sausage, bacon, etc., as long as it is a regular product, eat the right amount, you do not have to worry about safety.
(Content source Hengtianli Instrument Network)
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