Repeatability and Reproducibility of Determination of the Nitrogen Content of Fishmeal by the Combustion (Dumas) Method and Comparison with the Kjeldahl Method: Interlaboratory Study

Abstract

Ten fishmeal samples (hidden duplicates of 4 meals plus 2 high-protein meals as a Youden pair), tryptophan, and nicotinic acid were analyzed by 18 laboratories using the Dumas method. Thirteen of the laboratories also analyzed the same 12 samples using their current Kjeldahl method. Recoveries (± sR) of tryptophan and nicotinic acid were 99.3 ± 1.04 and 98.8 ± 2.11 by Dumas and 97.1 ± 3.03 and 74.6 ± 26.76 by Kjeldahl. The Dumas method gave significantly greater values (P < 0.001) than the Kjeldahl method. For fishmeals, Kjeldahl N 0.989 of Dumas N (P < 0.001). A similar proportionate difference (0.984 of Dumas N) was observed with tryptophan. Most laboratories failed to determine nicotinic acid correctly by Kjeldahl. For fishmeals, the relative standard deviations for repeatability and reproducibility were for Dumas 1.48 and 2.01% and Kjeldahl 1.62 and 2.37%, respectively. A single analysis conducted in 2 laboratories should not differ by more than 5.63% of the mean value when measured by Dumas or by more than 6.64% by Kjeldahl. It is concluded that with fishmeal, Dumas gives a more reliable measure of organic nitrogen than Kjeldahl, and, therefore, Dumas should be the method of choice.

Nutritional composition and sensory attributes of Alaskan flatfishes compared to plaice (Pleuronectes platessa)

“…The water content was determined gravimetrically after drying an aliquot of the homogenate for 12 h at 105°C. Protein nitrogen was measured with a LECO TruSpecN (LECO Instruments GmbH, Mönchengladbach, Germany) based on the principles of the Dumas combustion method (Miller et al ., ). Percent protein was calculated by multiplying% N by 6.25 (AOAC, ).…”

Chemometrics tools to distinguish wild and farmed meagre (Argyrosomus regius)

“…Such differences might be associated with a more balanced and rich protein diet in farmed meagre through controlled diets compared to a less balanced, variable and protein poorer diet in wild specimens. The Dumas method selected in this study to assess protein levels is considered as the most reliable method to measure organic nitrogen than Kjeldahl, being considered as the method of choice to assess protein levels in fishmeal samples (Miller, Bimbo, Barlow, & Sheridan, ).…”

Determination of Protein in Lupin Using Liquid Chromatography Coupled with Organic Carbon Detector and Organic Nitrogen Detector (LC-OCD-OND): Validation of a New Method

“…using a Dumas method generally show higher values than the Kjeldhal method [10]. Another reason would be that amino acids also occur in other forms, such as amides, glutamine and asparagine [9], which might contribute to higher measured protein values in Dumas method.…”