Determination of Milk Protein

Lifeasible specializes in milk protein detection and offers services to help detect crude and true protein content in milk and milk products.

Protein is one of the basic components of milk, and the protein content of milk is an important indicator of milk quality. There is a relationship between total nitrogen and protein nitrogen in milk. Protein nitrogen accounts for about 95% of the total nitrogen in milk. Therefore, the crude protein content of milk can be determined by testing the total nitrogen in milk. However, to measure the protein nitrogen content more precisely, it is necessary to separate the protein nitrogen and non-protein nitrogen. Then, the protein or non-protein nitrogen is determined to calculate the true protein content. Lifeasible offers services to help determine the crude protein content of milk and milk products and determine the true protein content directly or indirectly.

Our Services

We mainly determine the protein in milk and milk products based on the international standard Kjeldahl method. We also use other methods to determine the protein.

Kjeldahl method

The method is applied to obtain the milk's protein content by determining the milk's nitrogen content and calculating the protein content. To determine the nitrogen content, the sample is first digested with a mixture of concentrated sulfuric acid and potassium sulfate with copper sulfate as a catalyst. Subsequently, excess sodium hydroxide is added to the cooled digest to release ammonia. The released ammonia is distilled into an excess boric acid solution and titrated with a standard volumetric solution of hydrochloric acid.

Operation flow:

Determination of crude protein content:

We can help determine the crude protein content of a wide range of milk and milk products, including liquid cow's milk (whole, partially skimmed, or skimmed), goat's whole milk, sheep's whole milk, dried milk, dried milk products, and cheese. We can provide nitrogen determination based on the traditional method and block digestion method.

Direct or indirect determination of true protein content:

We use trichloroacetic acid to precipitate proteins from the test portion. The protein precipitates are then separated by filtration. We help determine the nitrogen content of the precipitates to obtain the true protein content directly. We can also help determine the non-protein nitrogen content of the remaining filtrate and the total nitrogen content to calculate the true protein content indirectly.

Main reference standards:
ISO 8968-1:2014
ISO 8968-3:2004
ISO 8968-4:2016

Other methods

We help detect proteins using various methods. In addition to the Kjeldahl method, the following methods are also available.

Dumas method:

We also help to estimate crude protein content based on the measurement of nitrogen content with the Dumas principle. The method refers to ISO 14891:2002.

Potentiometric titration method:

This method can exclude the interference of melamine and urea but cannot exclude the interference of ammonium nitrogen, which has some limitations.

Kormas Brilliant Blue G-250 method:

Coomassie Brilliant Blue G-250 binds to proteins and changes color in proportion to the amount of protein present. The intensity of the color is measured spectrophotometrically to determine the protein content.

UV spectrophotometric method:

The method exploits the absorption of UV light by proteins. It is fast and simple and allows the determination of true protein.

Infrared spectroscopy method:

The method is fast and efficient in the analysis of milk protein. It can also be combined with milk fat determination.

Bicarbonyl urea colorimetric method:

For this method, it is better to precipitate the protein with trichloroacetic acid and then assay it to exclude the interference of non-protein nitrogen such as melamine and urea.

Lifeasible offers services to help determine the crude protein content and true protein content of milk and milk products, and we also help determine the non-protein nitrogen content. Our services are professional and thoughtful. Please do not hesitate to contact us for convenient milk protein detection.