Nitrite analysis in meat: food safety and quality control

Meat provides an ideal environment for the development of microorganisms, which is why nitrites are commonly used as preservatives. These compounds inhibit bacterial growth, especially under pH conditions close to 6.

Analyzing the concentration of nitrites in meat products ensures that levels remain within the limits established by regulations such as the Codex Alimentarius and NTP (1999 Rev. 2019), thus guaranteeing food safety.

Equipment and reagents

To carry out nitrite analysis in meat, the following laboratory equipment and materials are required:

Laboratory equipment:

• Blender or laboratory homogenizer: to infuse the extract by mixing meat with ammonium aluminum sulfate.
• Centrifuge (recommended: Consul 22): with a minimum capacity of 250 ml, used to clarify the sample.
• Spectrophotometer: measures sample absorbance at 540 nm.

Adjustable heating plate: to maintain the temperature of the extract.

Click here to learn more about this equipment.

Required reagents (commercial or prepared in the lab):

• Sulfanilamide
• NED (naphthylethylenediamine)
• Distilled water
• Nitrite standard solution

Additional materials:

• Polypropylene tubes
• Volumetric flasks (250 ml and 25 ml)
• Glass pipettes and suction bulbs

Analysis process

1. Preparation of the meat extract

   Mix 30 g of meat with 50 ml of distilled water at 80 °C and heat for 15 minutes on a heating plate. Transfer the mixture to a 250 ml volumetric flask, fill up with hot water, and place in a steam bath for 2 hours, stirring occasionally.
   After cooling, add ammonium aluminum sulfate and centrifuge to obtain a clear extract. Fill up again to 250 ml with distilled water.

2. Calibration curve

   Prepare five nitrite standards ranging from 0 to 1 mg/l. Add 1.25 ml of NED to each, let stand for 5 minutes, then add 1.25 ml of sulfanilamide. Fill to 25 ml with distilled water, let rest another 5 minutes, and measure the absorbance at 540 nm.

3. Sample analysis

   Once the calibration curve is ready, proceed to analyze the prepared meat extract:

• Take 3 aliquots of 10 ml of the extract.
• Add 1.25 ml of NED, let stand for 5 minutes.
• Add 1.25 ml of sulfanilamide, fill to volume with distilled water, and wait another 5 minutes.
• Measure absorbance at 540 nm for each aliquot.

Interpretation of results

To determine the concentration of nitrites in the sample, apply the following formula:

NaNO₂ (mg/kg) = (L × 5 × 1000) / pm
Where:

• L = reading obtained from the calibration curve
• 5 = gravimetric factor to convert NO₂⁻ to NaNO₂
• pm = sample weight in grams

According to NTP (1999 Rev. 2019), the maximum permitted levels in meat products are:

• 130 ppm of nitrites (as residual nitrite ion)
• 365 ppm of nitrates (as residual nitrate ion

Nitrite analysis in meat products is essential to ensure chemical quality and food safety. Thanks to procedures like the one described and the use of laboratory equipment such as the Consul 22 centrifuge it is possible to verify that preservative levels remain within legal limits, protecting the final consumer and ensuring a high-quality product.