Protein content and its confusrons

There are different ways how the protein content in cereals is determined and expressed in the world markets, but no simple analytical method is available for the direct determination of the protein content in wheat (and other cereal products). In analytical chemistry some theses were assumed and a method for the easy calculation of the protein content based on the nitrogen analysis became a fact. It was assumed that proteins, present in various natural products, have a relatively consistent composition. From this assumption the relationship between the nitrogen content and the protein content, determined with rather complex methods, can be calculated. Methods for protein determination can be roughly divided into Reference and Prediction-Methods. The reference methods most commonly used in grain analysis are the Kjeldahl method, and its recent challenger, the Dumas, or combustion Nitrogen Analysis (CAN) method. Protein Determination by ICC Standard Methods: Protein can be determined according to ICC Standard Method No. 105/2 "Determination of Crude Protein in Cereals and Cereal Products for Food and Feed", (Kjeldahl Method) ICC Standard Method No. 167 "Determination of Crude Protein in Grains and Grain Products" (Dumas Method). The prediction methods for protein determination are based on the reflection or absorption of (infrared light) by a ground or whole grain sample (NIR/NIT). These methods, however, do not measure the nitrogen directly, but base the results on the correlation between the reflection or absorption of light with given wavelengths and the classical Kjeldahl or combustion analysis. Calibrations have to be made on a regular basis by a reference method when using these systems. ICC Standard Method: ICC Standard Method No. 159 "Determination of Protein by Near Infrared Reflectance (NIR) Spectroscopy" A fixed relationship between the amount of nitrogen and the amount of protein was assumed with app. 1 to 6. The amount of protein can be calculated from the nitrogen analysis by multiplying the nitrogen content with a fixed conversion factor. The confusions caused by the calculation from nitrogen to protein are: The conversion factor. Despite the fact that the factor 5.7 has been defined for wheat, 6.25 are also used for the protein calculation in wheat and wheat products in a number of cases and countries. But other factors are also used for the conversion: therefore, the conversion factor should always be mentioned with the result of a protein calculation, otherwise the results are not comparable. The moisture basis on which the protein content is calculated. Some of the most common moisture bases are: Australia 11% USA 12% Canada 13,5% UK 14% EU 0% (dry matter) Therefore, the moisture content used for calculation should also be mentioned with the protein results.