Analysis of calibration results for casein determination via indirect method ofinfrared spectroscopy [Analýza výsledků kalibraci pro stanovení kaseinu nepřímou metodou infračervené spektroskopie]

Casein measurement is important for cheesemaking and control of dairy cow nutrition. Reference Kjeldahl method is not suitable for routine purposes. Infra-red spectroscopy MIR and MIR-FT use can be a solutin. However,their casein specifity is relatively limited. Aim of the work was to assess the quality of performed calibrations for validation of calibration parameters. A retrospective analysis of MIR and MIR-FT calibrations was performed for estimation of limits their suitable parameters. Mean casein values of reference sample sets varied from 2.49 to 2.7% (2.61 ± 0.155). Mean variation range was 0.561 ± 0.164%. The mean correlation coefficient of calibration (KKK) was 0.974 ± 0.018 (P 0.001). The mean standard deviation of mean for individual differences (SDID) was 0.03 ± 0.011% (from 0.01 to 0.08). MIR-FT results were slightly better both for calibration and for proficiency testing. The high and low KKKs were higher in the case of accepted calibration as in proficiency testing for MIR-FT and MIR (0.986 0.964 and 0.970 0.948; 0.982 0.947 and 0.947 0.911; P 0.001). The casein number varied from 79.4 to 80.56% in bulk milk samples in three years,its variability was low from 1.4 to 1.5% relatively,which shows on relatively reliable casein analyses by methods MIR and MIR-FT. It does not need to agree f uly for individual milk samples. It is linked more to MIR than MIR-FT. Limits for acceptable calibration parameters were derived: ≥ 0.945 for KKK; 0.048 for SDID and 0.029% for mean difference as maximum.