Dumas Method Application for Non-Protein Nitrogen (NPN) Analysis in Milk Products

Non-Protein Nitrogen (NPN) refers to nitrogen-containing compounds present in biological samples that differ from the building blocks of proteins. NPN includes molecules like amino acids, urea, ammonia, and other nitrogenous substances crucial for various biochemical processes. It plays a pivotal role in assessing the nutritional status of food and feed products while preventing adulteration with non-protein nitrogen. Measuring NPN is not without complexity. The Kjeldahl method remains primary for determining protein and non-protein content in food. Analyzing milk via Kjeldahl yields "Kjeldahl" nitrogen, converted to "crude protein." However, 5-6% of milk's nitrogen exists as non-protein nitrogen, primarily urea, conventionally counted as protein using the standard Kjeldahl method. Determining NPN content and subtracting it from crude protein reveals the "true protein" value. Nevertheless, we have witnessed a shift towards the adoption of the Dumas method for protein analysis, gradually displacing the Kjeldahl method due to its speed, throughput, and the elimination of hazardous chemicals—albeit without established methods and norms to account for NPN. Dumas and Kjeldahl differ in principles but share nitrogen content measurement. Dumas excels in efficiency, throughput, and precision by measuring total nitrogen, encompassing both protein-bound and non-protein nitrogen. This method involves sample combustion, converting nitrogen to nitrogen gas. This abstract showcases Dumas method's application in milk samples, effectively determining "true protein" by subtracting NPN, referencing ISO 8968-4 (Kjeldahl) as the method. Importantly, Dumas method's scope extends beyond milk products.