Milk Nitrogen Testing

Milk nitrogen detection is one of the important indicators for evaluating milk quality. Its main purpose is to determine the nitrogen content in milk, thereby indirectly calculating the protein content in milk. The following is a detailed introduction to milk nitrogen detection:

1. Detection principle
Milk nitrogen detection is usually based on the Kjeldahl method or its improved method. The principle of the Kjeldahl method is to digest the milk sample, heat and distill it in an alkaline solution, so that ammonia is free and evaporated and absorbed by the boric acid solution, and then titrate with a hydrochloric acid standard solution and calculate the nitrogen content. In addition, there are modern analytical methods such as high-performance liquid chromatography (HPLC), which have higher sensitivity and accuracy.

2. Detection steps
Sample preparation:
Take an appropriate amount of milk sample to ensure that the sample is representative.
Pre-treat the sample, such as dilution, filtration, etc., to remove impurities and interfering substances.
Digestion:
Add concentrated sulfuric acid and a catalyst (such as copper sulfate and potassium sulfate) to the digestion tube to digest the milk sample until it is clear and transparent.
The temperature and time need to be controlled during the digestion process to ensure complete digestion.
Distillation:
The digested sample is transferred to a distillation apparatus, and an alkaline solution (such as sodium hydroxide) is added and heated for distillation.
Ammonia is released from the sample and absorbed by the boric acid solution.
Titration:
The absorbed ammonia is titrated with a hydrochloric acid standard solution, and the volume of hydrochloric acid consumed is recorded.
The nitrogen content in milk is calculated based on the volume and concentration of hydrochloric acid consumed.
Data processing:
The measured nitrogen content is converted into protein content, and the protein content is usually estimated by multiplying the nitrogen content by a factor of 6.25.
The data is statistically analyzed to evaluate the protein quality of milk.
III. Detection method
Kjeldahl nitrogen determination:
Classic method, suitable for rapid detection of a large number of samples.
However, the operation is cumbersome and requires strict control of digestion and distillation conditions.
High-performance liquid chromatography (HPLC):
Modern analytical method with higher sensitivity and accuracy.
Multiple components, such as protein, amino acids, etc., can be detected simultaneously.
But the equipment is expensive and the operation is complicated.
Near-infrared spectroscopy:
Analysis based on the spectrum generated by irradiating the sample with near-infrared light.
Fast, non-destructive, and no pretreatment required.
However, a model needs to be established for calibration and verification.
IV. Precautions
Sample preservation:
Milk samples should be tested as soon as possible to avoid long-term storage and deterioration.
Samples should be stored in a low-temperature, light-proof environment to reduce the loss of nutrients.
Instrument calibration:
Regularly calibrate and maintain the testing instruments to ensure the accuracy of the test results.
Operation specifications:
Strictly follow the test methods and operating procedures to avoid human errors.
Safety protection:
Pay attention to personal protection during the test and avoid contact with toxic and harmful substances.
In summary, milk nitrogen testing is one of the important means to evaluate milk quality. By choosing appropriate test methods and strictly abiding by operating procedures, the accuracy and reliability of the test results can be ensured.