Implementación del Método Kjeldahl para la determinación de proteína para diferentes matrices en el Laboratorio ECUACHEMLAB Cía. Ltda.

Abstract

The validation of analytical methods is a very important task for the laboratories of analysis. Are performed with the aim of generating reliable results, based on documented evidence to support their veracity. Particularly, for the determination of nitrogen and protein in food, the Kjeldahl method is set, which one is currently used as official method by several national and international agencies.

In the development of this work, the AOAC Official Method 2001.11 was used, which describes the procedure by Kjeldahl distillation for the measurement of crude protein. With the collection and processing of the data, working ranges were establishedwhich varied from 9 to 23%, 7 to 34% and 0.3 to 24% for matrices of meat, cereals, milk and its derivatives, respectively. The accuracy of the method was assessed by the value of the coefficient of variation (CVr) lower than 5%, which criterion was fulfilled at all points of each matrix.

Additionally, the limits of repeatability and reproducibility were calculated, allowing to evaluate the absolute difference between duplicates in subsequent analysis, the appropriate values in repeatable conditions must be lower than or equal to 0.39 for Meat, 0.28 for cereals, and 0.24 for dairy products, 0.43 for meat, 0.32 for cereals and 0.22 for dairy products in reproducible conditions. On the other hand, the accuracy was verified by the statistic Z score for matrices of meat and cereals, analyzing certified reference materials (NIST) and intercomparisons requested to LGC. For the matrix of dairy products, it was found the recoverability of certified reference materials as well as that of the primary standard ammonium sulphate. Finally, the factors of uncertainty for meat, cereals and dairy products were established as 0.030, 0.021 and 0.014, respectively.