Protein Determination after DUMAS in Milk and Milk Products


Perfect and easy analysis for solid and liquid products.

Protein is one of the most significant nutrient components in milk products. The accurate and precise determination of protein not only plays a role in the characterization of nutritional or dietary value of milk products but is also the key to determining the economic value of these materials. Protein in milk products is most commonly calculated using the measured total nitrogen content in the sample and a multiplier or conversion factor (typically 6.38). Nitrogen determination is performed using either the classical wet chemical method (Kjeldahl), or a combustion method (Dumas).

The LECO FP828 or FP929 product lines are combustion Nitrogen/Protein determinators that utilize a pure Oxygen environment ensuring complete combustion and superior analyte recovery. A thermoelectric cooler removes moisture from the combustion gases before they are collected in a ballast. The combustion gases equilibrate and mix in the ballast before a representative of the gas is extracted and introduced into a flowing stream of inert gas (Helium or Argon) for analysis. The aliquot gas is carried to a thermal conductivity cell (TC) for the detection of Nitrogen (N2). Thermal conductivity detectors work by detecting changes in the thermal conductivity of the analyte gas compared to a reference/carrier gas.

LECO FP828 & FP929 Protein Analyser, Auto Sampler

Picture 1: LECO FP828 and FP928 Dumas protein analysers

Whereas the 828-product line uses foils or capsules for solid samples like cheese, milk powder or yoghurt to be entered in the vertical furnace system, the 928 series works with big, reusable combustion boats in a horizontal furnace.

Sample Name Mass [g] Repetitions % N % Protein
Whole Milk ~0.5 5 0.520 ± 0.008 3.32 ± 0.05
Skim Milk ~0.5 5 0.547 ± 0.003 3.49 ± 0.02
Half & Half ~0.5 5 0.467 ± 0.005 2.98 ± 0.03
Powdered Milk ~0.15 5 5.91 ± 0.01 37.7 ± 0.1
Swiss Cheese ~0.25 5 3.02 ± 0.02 19.3 ± 0.1
Parmesan Cheese ~0.25 5 4.76 ± 0.02 30.4 ± 0.1
Infant Formula ~0.15 5 1.90 ± 0.01 12.1 ± 0,1

Table 1: Typical results of dairy products for LECO FP828 Dumas Protein analyzer. More applications are available on request. Samples were measured with 10 cc aliquot and Argon carrier gas.

This data shows perfect precision and accuracy for some typical dairy products. More data is available in the following application notes.

A big advantage of the LECO DUMAS protein analyzers in the dairy field is the easy possibility to run liquid and solid samples without any special handling. Just use on the 828-product line big open tin capsules and enter ~0.5g of liquid samples with an eye dropper or use the 928 series metal boats or ceramic boats with a nickel liner. So, no awkward packing of liquids into containers, no additional liquid autosampler or second analyzer is needed.

The special LECO advantages for dairy samples can be summarized:

  • Ballast Aliquot system for lowest costs per analysis and lowest maintenance;
    e. g.: reduction copper can last up to 4,000 analysis
  • Analysis times in less than 3 minutes on the 828-product line
  • Combustion in pure Oxygen for matrix independency, fill recovery and low analysis costs, even for unknown samples
  • Easy handling of liquid samples, no wrapping, special treatment, use of absorption chemicals etc.
  • Robustness for routine work either in laboratory of product line environments
  • Compliant to ISO 14891: Milk and Milk Products – Determination of Nitrogen Content
  • LECO service team with more than 25 subsidiaries around the globe

If you are interested in further information, be free to contact us.

Banner_liquid-samples_1200x628pxJoin us for our upcoming LECO online webinar, "Easy Analysis Of Liquid Samples With LECO Protein Analysers Focused On Dairy Samples," to delve deeper into the world of protein determination in both solid and liquid samples.

Register now to enhance your understanding and stay at the forefront of protein analysis technology.

Tuesday, 02 Apr 2024 | 11:00 am

Register now

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