Determination of crude protein in macaroni products by the combustion method and comparison with the Kjeldahl method: Interlaboratory study

Abstract

An interlaboratory study was conducted to evaluate the reproducibility of a combustion method for determining crude protein in macaroni products according to the Japanese Agricultural Standard (JAS). Fourteen participating laboratories analyzed five test materials (five pairs of blind duplicates) of macaroni products by the combustion method. Six different types of instruments commonly used for the combustion method in Japan were included in this study. After removal of statistical outliers, the repeatability and reproducibility of this method were found to be 0.16 - 0.53 % and 0.89 - 1.1 %, respectively. The HorRat values of this method were 0.25 to 0.31. The results for the combustion method were compared with those for the Kjeldahl method used on the same test materials and reported previously. Differences of means between the two methods were 0.10 - 0.13 % in five test materials. The differences did not considerably affect judgment near the standard values 11 % and 12 % of the JAS.