Food Safety – What is the Kjeldahl Method and Why Does It Matter?

Food labels may not be an exciting topic, but it is a legal requirement to disclose the amount of protein a food product contains. There are multiple methods that can be employed to ascertain protein levels, but one of the most long-standing and reliable methods is known as the Kjeldahl method, which has been employed for well over a century.

Let’s dive into the history of Kjeldahl, and why it’s still used today!

Principles of Kjeldahl

The inventor of the Kjeldahl method, Johan Gustav Christoffer Thorsager Kjeldahl, was a chemist based within the Carlsberg (probably the best lager in the world) Laboratory in Copenhagen during the latter half of the 19th century. He was tasked with developing a method to determine the protein levels of grain processed during the malting stage, as a lower protein level led to a higher final yield of beer.

Ultimately the Kjeldahl method can be broken down into 3 key stages: digestion, distillation and finally titration.

Digestion: A sample (homogenous) is added to concentrated sulfuric acid (H2SO4) and boiled, producing an ammonium sulphate solution.

Distillation: Addition of excess strong base (NaOH frequently) to the cooled post-digestion solution releases the nitrogen as (quantifiable) free NH3. After being subjected to steam distillation, the ammonia gas is trapped in dilute boric acid.

Titration: Finally, titration with a standard acid is employed to quantify the amount of ammonia ions, which allows the calculation of Nitrogen content.

Total Kjleldahl Nitrogen (TKN) is the sum of nitrogen bound in organic substances, and is the figure calculated by the method, with a single simple calculation TKN can be used to infer total protein. To calculate this a conversion factor is employed and while this differs between different food products, 6.25 is what is employed almost universally in practice.

Although not the fastest analytical method currently employed, it is robust and highly reliable (slow and steady wins the race!) so is still a gold-standard within the industry.

VELP Scientifica

We at a1-envirosciences are proud to be the sole UK distributor of VELP Scientifica’s specialised digestor and distillation units, which are designed to perfectly complement each other and allow for accurate and reliable high-throughput Kjeldahl analysis.

Both come in semi and fully automatic flavours, allowing for ease of use within the laboratory and maximising efficiency/workflow. The automatic distillation units (both the UDK 159 and 169) come with integrated colorimetric titrator, meaning that Kjeldahl analysis has never been safer nor easier!

If you want to take your Kjeldahl analysis to the next level or are interested in discussing our range of VELP products, give us a ring on 0845 873 8181 or get in touch with us by email: