Protein is the parameter that sells pulses, and it is also the parameter most often quoted in a form that cannot be verified. A buyer who receives two certificates showing different protein figures for the same lot is usually not looking at a dispute about the lot. They are looking at two different calculations, both arithmetically correct.
This guide sets out what a protein figure is actually made of, why pulse and cereal protein are complementary rather than interchangeable, and how to write protein into a specification so that it can be tested.
Crude protein is a calculation, not a measurement
The standard laboratory route does not measure protein at all. It measures nitrogen – by Kjeldahl digestion or by Dumas combustion – and multiplies it by a conversion factor to estimate protein. The historic general factor of 6.25 assumes a fixed nitrogen content in protein, which is an approximation, and different commodity conventions use different factors.
This matters commercially because a lot analysed with one factor and reported against a specification written with another will appear to fail when it has not. The remedy is one line in the contract: state the conversion factor alongside the target. See protein content for the definition.
Dry matter basis is the second variable
A protein figure can be reported as-is, on the material as received, or on a dry matter basis with the moisture removed from the calculation. Since dry pulses carry meaningful moisture, the two figures differ by a commercially significant margin.
Neither basis is wrong. Reporting one against a specification written in the other is wrong. Because a dry-basis figure is always the higher number, a supplier quoting a dry-basis protein against an as-is specification is quoting a flattering figure. Require both, and require the moisture result with its method – see moisture content and dry matter.
Three things convert a protein claim into a contractual figure: the analytical method, the nitrogen conversion factor and the moisture basis. Missing any one of them and the number is decorative.
Method: Kjeldahl and Dumas
Kjeldahl is the long-established wet chemistry route; Dumas combustion is faster and now dominant in commercial laboratories. Validated collaborative methods exist for both, and results are generally close but not identical. For a contract, name the method and require the laboratory to hold accreditation to ISO/IEC 17025 for it. An accredited result is defensible; an unaccredited one is an opinion. The certificate of analysis should carry both the method and the accreditation scope.
Near-infrared instruments are widely used for rapid screening at intake. NIR is excellent for sorting and for process control and is a calibration against a reference method, not a replacement for it. Contractual figures should come from the reference method.
Why pulse protein and cereal protein are complementary
The nutritional story is about amino acid composition rather than quantity. Pulse proteins are relatively rich in lysine and relatively limited in the sulphur-containing amino acids, methionine and cysteine. Cereal proteins are the mirror image: adequate in the sulphur amino acids and limited in lysine.
Combining the two in a formulation gives a better amino acid profile than either alone. This is the technical basis for the pulse-and-cereal pairings that appear in traditional cuisines everywhere, and it is why a formulator working on a plant-protein product usually blends rather than substituting a single source.
Protein quality is scored, in the framework recommended by FAO expert consultation, using digestible indispensable amino acid scoring. The practical implication for a buyer is that a raw protein percentage is a poor proxy for nutritional value, and that a nutrition or health claim in the Union has its own legal framework which a supply specification does not satisfy on its own.
Typical relative position of the main species
Absolute figures vary by variety, season and growing conditions, so the table below is a relative ordering rather than a specification. Where protein is the traded parameter, test the lot.
| Material | Relative protein position | Practical note |
|---|---|---|
| Soya | Highest of the common food legumes | Sets the benchmark that other pulse proteins are compared against |
| Lupin, mung, faba | High | Growing interest in isolate and concentrate routes |
| Lentils, peas, chickpeas, beans | Moderate to high | The volume pulse trade; protein is a selling point but rarely the traded spec |
| Wheat, maize, rice | Substantially lower | Complementary amino acid profile rather than a competing source |
Within a single species, growing conditions move protein more than variety does. A dry finish concentrates protein and reduces yield; a wet finish does the reverse. That is why a buyer contracting a protein minimum should either contract against tested lots or accept a wider band in a difficult season.
Protein in a specification: what to write
- Target and minimum, with the basis stated explicitly as-is or dry matter.
- Nitrogen conversion factor.
- Analytical method and the requirement for ISO/IEC 17025 accreditation.
- Moisture with its own method, since it underpins the basis conversion.
- Sampling plan, because protein varies across a lot more than buyers expect.
- Retest and arbitration route if the parties disagree.
Where the protein story leads commercially
For most of the pulse trade, protein is a marketing attribute rather than the traded parameter; the contract is written on cleanliness, calibre and cook behaviour. Protein becomes the traded parameter in the ingredient trade – flours, concentrates and isolates – which is covered in the flour and isolate guide. Labelling of protein content on a finished product in the Union sits under the food information regulation, which places the obligation on the operator marketing the product rather than on the raw material supplier.
For the raw material records see chickpeas, red lentils and dried peas.