| Popis: |
This study was carried out within the framework of the European COST 902/FLAIR-programme (European Cooperation in the Field of Scientific and Technical Research). The first objective was the harmonization of certain techniques currently used for the determination of nitrogen fractions of cheese. The second objective was to determine the repeatability (r) and reproducibility (R) of the standardized methods including the determinaiton of total nitrogen (TN), water soluble nitrogen (WSN), nitrogen soluble at pH 4.4 (SN 4.4), ethanol soluble nitrogen (ESN), nitrogen soluble in trichloroacetic acid (TCA12-N) and nitrogen soluble in phosphotungstic acid (PTA-N). The r- and R-values for TN were in the range of O.3 to 1.4 and 1.4 to 2.5 g/kg, respectively. For all other methods tested, the r-values were in the range of 0.1 to 1.1% of TN, the R-values were below 3.3% of TN except for ESN (5%). For most cheeses tested, the WSN and SN 4.4 results were highly correlated, as were the TCA12-N and ESN results. Therefore, only a limited number of methods should be applied in practice, other aspects should be considered such as practical and environmental aspects (e.g. toxicity of solvents) and future use of the fractions and the kind of cheese. The difference between the TCA12-N and PTA-N values as well as the difference between SN 4.4 and TCA12-N values were used to characterize protein breakdown. |
