Interlaboratory Study on the Determination of Crude Protein in Macaroni Products on JAS by Kjeldahl Method Using Copper Catalysts

Abstract

The Kjeldahl method using copper catalysts for digestion was established as an analytical method for the determination of crude protein in macaroni products in the Japanese Agricultural Standard (JAS). An interlaboratory study was performed to evaluate this Kjeldahl method. Eleven participating laboratories independently analyzed five test materials (five pairs of blind duplicates) of macaroni products. After removal of statistical outliers, the repeatability (RSD_r) and reproducibility (RSD_R) of the evaluated methods were 0.25-0.59 % and 1.2-1.5 %, respectively. The HorRat values (RSD_R (%)/predicted RSD_R (%)) of the total nitrogen content were calculated to be at 0.32 to 0.43. This method was shown to have acceptable precision in this study.