Proteins, complex organic compounds made of amino acids, are important components of agricultural products such as grains, feeds and food products as well as nutritious sources. Thus protein content determination and component analysis is important, especially for businesses such as food industry, agricultural product processing industry, food and nutrition, food and health, international trade and crop breeding, in which protein determination is highly valued.
The determination of protein is based on the Kjeldahl nitrogen determination methods, which quantify the protein contains in a sample through quantifying the amount of nitrogen which generally holds the consistent ratio in certain kind of protein. The quantified amount of nitrogen through this method consists of both the protein nitrogen and non-protein nitrogen, which might be organic or non-organic, so it is called crude protein amount. Common protein contains about 16% nitrogen, which means 6.25 grams protein contains 1 gram nitrogen, so 6.25 could be called protein factor, which could be symbolized with a ‘K’. So if it is desired to determine % protein instead of % nitrogen, the calculated % N is multiplied by a factor, the magnitude of the factor depending on the sample matrix. Many protein factors have been developed for use with various types of samples. The list below represents just a few of the factors described in the standard methods of analysis.