As Dumas and NIR analysis methods become increasingly efficient, modern laboratories can seriously consider a range of protein options beyond traditional Kjeldahl analysis. Here are some summaries of what to use and when, including:
- The advantage of the Dumas method
- Why Kjeldahl analysis is not going away
- The potential of NIR analysis for adulteration screening
The advantage of the Dumas method
Automation features of Dumas equipment make it less time-consuming compared to Kjeldahl analysis. Dumas is also faster with the test result available five minutes after preparation.
Dumas is ideal when a particular sample type needs to be tested on a regular basis, but for labs that need to run just a few tests on different sample types it is not the optimal solution. Because Dumas equipment takes some time to start-up, it lends itself to continuous operation. Kjeldahl, on the other hand, can be used for on-the-spot testing anytime.
Why Kjeldahl is not going away
Where a sample is unfamiliar and where the laboratory performs occasional low-volume tests, then the predictability of Kjeldahl makes the established reference method a practical choice. With Kjeldahl, you can manage more sample size up to around 10 grams, but with Dumas, the maximum you can handle, even with a Macro version, is one gram.
The potential of NIR analysis
Near infrared (NIR) analysis is gaining benchtop space in laboratory operations, especially for areas such as animal feed. The strengths of NIR as a common reference that is simple to align via new connectivity technology and the fact that it has a clear advantage for screening for abnormalities.
The systems used for many years in the dairy and grain industries where reference laboratories regularly check NIR against reference analysis via a ring test of common samples to maintain and monitor calibrations.
Another strength of NIR is its capability as a screening technology where a known spectral fingerprint is used as a model for a good sample. The screening check is performed simultaneously with the compositional tests for protein, moisture and so on. An advanced form of screening can be performed where the NIR instrument is programmed to recognize the spectral fingerprint of known adulterants such as melamine.
With Dumas and Kjeldahl the scope is to quantify the total nitrogen. NIR is a unique opportunity to tackle adulteration because the technology is widespread, it can share the spectral data so no matter where the test is performed you can then evaluate elsewhere if required.
Protein methods: a summary
Kjeldahl
- In 2009, the European Commission confirmed the Kjeldahl method as an official method for food and feed control.
- Determines Nitrogen based on organic Nitrogen and ammonia.
- A wet chemistry technique invented by Johan Kjeldahl at Carlsberg laboratories back in 1883 although modern Kjeldahl solutions are highly refined for batch handling making it possible to handle up to 20 samples at a time.
- Sample size is not limited, making it a valuable method for inhomogeneous sample types.
Dumas
- A relatively new method for food and agri, but very popular for feed and increasingly defined in standards.
- Determines total Nitrogen including inorganic fractions.
- A combustion method invented in 1883 by Jean Baptiste Dumas in which an exothermic reaction instantaneously transforms any organic material into its element – no chemicals involved.
- Fast and convenient with highly automated analysis of batches of up to 117 samples at a time, but with limited sample size due to the combustion method employed.
NIR
- A spectroscopic technique that makes use of the naturally occurring electromagnetic spectrum defined by wavelengths between 700nm and 2500nm.
- Introduced in the seventies and eighties in some food and agri industries and has become indispensible for quantitative determination of the major constituents in most types of food and agricultural products.
- Requires a calibration according to the application, but once this is in place, there is little or no sample preparation and no chemicals or consumables involved. It is operator friendly and fast (30-60 seconds).
- Growing in use in line with availability of readymade calibrations advances in computing power and networking connectivity technology.
Related Products
Kjeltec 9 Distillator
The KjeltecTM 9 Distillator is a fully automated distillation unit designed primarily for Kjeldahl analysis, but widely used for many different distillation applications.
Kjeltec 9 Analyser
Kjeltec 9 analyser provides fully automated Kjedahl analysis and is verified against official standards (AOAC, EPA, DIN, GB, and ISO) for simplified validation. Take advantage of fast turnaround time, improved data handling and less risk of human error for accurate results.
KT 200 Kjeltec
The KT 200 Kjeltec™ Distillation unit provides a simple and reliable solution for safe and semi-automatic distillation for protein determination. The possibility to pre-program alkali addition and distillation time supports the production of accurate results independent of operator.
