Protein | EUROLAB

What Is Protein?

Protein determination is the measurement of the total amount of nitrogen in food and converting it to protein content with an appropriate conversion factor. In the Kjeldahl method, the sample is burned with sulfuric acid and the released nitrogen is determined by titration; In the Dumas method, the sample is burned at high temperature and the nitrogen gas formed is measured.

Purpose of Protein

The purpose is to provide data for the nutritional value claim and to verify that the protein content of the product complies with the specification. It is one of the basic items of the nutritional declaration table within the scope of (EU) 1169/2011.

Which Products Is Protein Applied To?

Milk and dairy products
Meat and meat products
Flour, grains and legumes
Baby food and special nutritional products
Protein takviyeleri

In Which Sectors Is Protein Used?

FoodAgricultureRetailPharmaceuticals

Standards Related to Protein

TS EN ISO 1871 (food and feed — general principles of nitrogen determination, Kjeldahl)
TS EN ISO 16634-1/-2 (total nitrogen by combustion method — Dumas)
TS EN ISO 8968 series (milk — nitrogen content)
TS EN ISO 20483 (cereals and pulses — nitrogen and crude protein)

Protein Conditions

Conversion factor: Varies depending on product type; Different factors are used and reported in milk and cereal
Yakma: Acid burning in Kjeldahl, high temperature burning in Dumas
Result: In percent by mass; Can also be given on a dry matter basis

Equipment for Protein

Kjeldahl combustion and distillation system
Dumas nitrogen analyzer
Analytical balance
Automatic titrator

Sample Requirements for Protein

Homogenized representative sample
Approximately 0.5–1 g of sample
Product type and target protein value, if any, should be reported
If moisture content is measured separately, results can be given on a dry matter basis

Duration of Protein

The Dumas method is fast and provides results in a short time per sample. Kjeldahl is longer due to the combustion and distillation steps.

Protein Procedure

1The sample is homogenized and weighed.
2It is burned with sulfuric acid and catalyst in Kjeldahl.
3Ammonia is collected by distillation and titrated.
4In Dumas, the sample is burned at high temperature and nitrogen gas is measured.
5Total nitrogen is calculated.
6It is converted into protein content with the appropriate conversion factor.

Protein Acceptance Criteria

The acceptance criterion is the product specification or label declaration. (EU) 1169/2011 provides tolerance guidelines for declared nutritional values; The tolerance to be applied varies depending on the product and nutrient and is confirmed by the applicable guideline.

Evaluation of Results

The method measures total nitrogen, not actual protein: nitrogen-containing non-protein substances increase the result. This is the basis of historical cases of adulteration. When the actual protein question is required, amino acid profile or non-protein nitrogen determination is performed separately.

Protein Report

Sample description and product category
Applied method (Kjeldahl/Dumas)
Nitrogen–protein conversion factor used
Total nitrogen and protein result
Measurement uncertainty

Accreditation

EUROLAB holds internationally recognised accreditation obtained from accreditation bodies party to the IAF and ILAC multilateral recognition arrangements, under ISO/IEC 17025 for laboratory testing, ISO/IEC 17020 for inspection and surveillance, and ISO/IEC 17021-1 and ISO/IEC 17065 for system and product certification. This chain ensures the reports and certificates issued are accepted worldwide.

Whether this test can be offered within accredited scope depends on your product and the standard applied; since accreditation is method-based, the scope is confirmed in writing at the quotation stage.

Scope and authorisations

Related Regulations

Regulation (EU) 1169/2011 on Food Information to Consumers

Food Testing — What Does This Testing Field Cover?

The section below describes the field that the Protein test belongs to; the conditions and acceptance criteria of this particular test are given in the sections above. The scope specific to your product is confirmed in writing at the quotation stage.

Food testing shows that a product is safe for consumption and contains what its label states. The family works along three axes: microbiological safety, chemical safety and nutritional composition. All three require different laboratory infrastructure, a different body of methods and a different turnaround time.

The most distinctive feature of the field is TIME PRESSURE. A steel specimen can wait on a shelf; a raw milk or fresh meat sample cannot. The time the sample was taken, the transport temperature and how long it takes to reach the laboratory directly determine the validity of the result. In food microbiology the cold chain record is therefore an inseparable part of the test report.

On the microbiological side there are two different questions and they must not be confused. DETECTION of a pathogen is a qualitative question: is Salmonella present in the sample or not? ENUMERATION of indicator organisms is a quantitative question and an indicator of production hygiene. The absence of a pathogen in a product does not show that hygiene is good; if the total mesophilic aerobic count is high, there is a problem in the process.

On the chemical side, pesticide residues, mycotoxins, heavy metals, additives, veterinary drug residues and process contaminants (acrylamide, furan, PAH) are measured. Multi-residue methods in this area (QuEChERS-based LC-MS/MS and GC-MS/MS) can screen hundreds of active substances in a single analysis; limits are defined separately for each product–substance pair.

On the composition side, protein, fat, moisture, ash, fibre, sugar profile, fatty acid composition, vitamin and mineral content are determined. These values are the basis of the nutrition declaration on the label and the tolerance ranges are defined in legislation — the difference between the declared value and the measured value must stay within that tolerance.

There is NO CE marking on food, and this shapes how the field works. Conformity is demonstrated through operating a HACCP-based food safety system, complying with labelling rules and not exceeding contaminant, residue and microbiological limits. A test result produces evidence not for a certificate but for a functioning system.

Allergen management carries particular weight. The presence of an undeclared allergen in a product is one of the most frequent causes of food recalls. Analysis here runs together with cleaning validation: it is shown that the line has been cleaned adequately after a production run containing an allergen and that the risk of cross-contamination is under control.

Voluntary schemes have become effectively mandatory in this field. Retail chains require their suppliers to hold a certificate under a GFSI-recognised scheme (BRCGS, IFS, FSSC 22000); without it, getting onto the shelf is practically impossible.

Method groups in this field

Pathogen detection
Detection of Salmonella, Listeria monocytogenes, Campylobacter, Cronobacter and Shiga toxin-producing E. coli; culture-based and molecular methods.
Indicator counts
Total mesophilic aerobic count, Enterobacteriaceae, coliforms and E. coli, coagulase-positive staphylococci, yeasts and moulds, lactic acid bacteria, sulphite-reducing Clostridia.
Pesticide and veterinary residues
Multi-residue screening by LC-MS/MS and GC-MS/MS with QuEChERS extraction.
Mycotoxins and contaminants
Aflatoxins, ochratoxin A, deoxynivalenol, patulin; heavy metals (ICP-MS), acrylamide and PAH compounds.
Nutritional composition
Kjeldahl protein, fat and fatty acid profile, moisture, ash, dietary fibre, sugar profile, vitamin and mineral analyses.
Allergens and authenticity
Gluten, milk, egg, nut and soy allergen analyses; molecular methods for species identification and adulteration detection.

Commonly confused in this field

Sampling is half the result. A sample transported at the wrong temperature or delayed gives an invalid result even if it is analysed correctly in the laboratory.
The absence of a pathogen does not show that hygiene is good; indicator counts give separate information and the two are read together.
A result from a sample taken from a lot can be generalised to the whole lot only if the sampling plan was set up statistically.
Limits are defined in separate regulations by product group and are updated regularly; a conformity decision based on an outdated limit table may be wrong.
For exports, the limits of the destination country may differ from EU limits; the same product may be compliant in one market and non-compliant in another.

Which decisions these results support

Verification of the HACCP plan and process monitoring
The basis for the nutrition declaration and allergen information on the label
Health certificates before export and compliance with destination market limits
Supplier and lot-based acceptance control
Shelf-life studies and determining storage conditions
Producing evidence for audits under GFSI-recognised schemes

Related Tests

Frequently Asked Questions About Protein

Do Kjeldahl and Dumas give the same result?

It gives close results but may not be exactly the same; While Dumas captures all nitrogen forms, Kjeldahl may not fully convert some forms. Whichever method the specification requires is applied and the report specifies the method.

Why does the conversion factor vary by product?

Because the nitrogen content of different proteins is different. Milk proteins and grain proteins do not carry the same amount of nitrogen; Therefore, factors specific to product groups are used and stated in the report.