Evaluation of a direct method for the determination of true protein content in milk by Kjeldahl analysis

The recent adoption by the AOAC of a direct method for determination of protein nitrogen content of milk provides a verified technique for obtaining true protein content via a single Kjeldahl digestion and titration rather than requiring two digestions/titrations, as specified by the established indirect method. The direct method is not applicable when the non protein nitrogen content is required to be known. An investigation was undertaken to gauge the robustness of this direct method and to compare its results to those provided by the indirect method, when applied to natural and artificial milk samples comprising a wide range of fat and protein contents. The direct method provided a saving of time and materials over the indirect method and gave comparable results, satisfying the statistical parameters of repeatability and reproducibility as specified by the current Australian Standard indirect method