The determination of the total protein content is an essential tool for quality control and protein declaration according to international labeling laws in the food & feed industry and research facilities. Protein content can directly correspond to product properties and classifications e.g. dough properties, foam formation, the taste of beer, or the differentiation between starch and gluten-free starch. In all application areas highly precise, matrix- independent protein analyses are required.
In principle, protein quantification is achieved via a series of specific and non-specific physical and chemical reactions followed by suitable detection. Full method automation as well as accordance to industry standards is generally desirable in current laboratory operations, which has led to two different widely accepted primary methods for the determination of total protein content: the wet chemical method according to Kjeldahl and the high-temperature combustion method according to Dumas. As a secondary analysis method near infrared spectroscopy (NIRS) can be found, however, this method requires a primary method for calibration purposes.
For more than 100 years the Kjeldahl principle was the most commonly used method and described in the majority of standards for the determination of total protein content of food products. As a wet chemical analysis it is time consuming, labor-intensive and requires hazardous and toxic chemicals. All this is nowadays unwanted with regard to laboratory safety but also for economic reasons. This explains the trend in recent years that the Kjeldahl principle is more and more displaced by the Dumas principle.
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