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AOAC
2001.14
Nitrogen (Total) in Cheese: Kjeldahl Method
2004 (2023)
Final Action
5
AOAC 2023 Online Ch. 33.7.12A
Cheese is digested in H2SO4, using CuSO4∙5H2O as catalyst with K2SO4 as boiling point elevator, to release N2 from protein and retain N2 as ammonium salt. The initial 1 g test portion size assures an adequate amount of H2SO4 remaining at the end of digestion. Concentrated NaOH is added to release NH3, which is distilled, collected in H3BO3 solution, and titrated.