Combustion Nitrogen Analyses (CNA) is one of several methods used to determine protein content in flour or wheat.

Method
1. A sample of flour or ground wheat (0.15 to 0.20 grams) is weighed and placed into a CNA protein analyzer.
2. This process is fully automated and begins by dropping the sample into a hot oven where it is burned at 952 degrees Celsius.
3. The amount of nitrogen gas released during burning is measured and a formula is applied to convert this measurement to protein content in the sample.


Results
• Protein content is determined through high temperature combustion in a protein analyzer. Since protein is the major wheat compound that contains nitrogen, the protein content can be determined by measuring the amount of nitrogen released during burning.
• Protein content results are expressed as a percentage of the total sample weight; for example, 10 percent protein content on 12 percent moisture basis for wheat or 8.5 percent on 14 percent moisture basis for flour.


Why is this important?
Protein content is a key specification for wheat and flour purchasers since it is related to many processing properties, such as water absorption and gluten strength. Protein content also can be related to finished-product attributes, such as texture and appearance. Low protein content is desired for crisp or tender products, such as snacks or cakes. High protein content is desired for products with chewy texture, such as pan bread and hearth bread.
Bakers use protein content results to anticipate water absorption and dough development time for processes and products, because higher protein content usually requires more water and a longer mixing time to achieve optimum dough consistency.
Combustion Nitrogen Analysis (CNA) is often used to develop calibrations for other protein methods, such as Near Infrared Transmittance (NIRT) or Near Infrared Reflectance (NIRR).
Adapted from Method 46-30, Approved Methods of the American Association of Cereal Chemists, 10th Edition. 2000. St. Paul, MN.