A comparison of result reliability for investigation of milk composition by alternative analytical methods in Czech republic

Abstract

The milk analyse result reliability is important for assurance of foodstuff chain quality. There are more direct and indirect methods for milk composition measurement (fat (F), protein (P), lactose (L) and solids non fat (SNF) content). The goal was to evaluate some reference and routine milk analytical procedures on result basis. The direct reference analyses were: F, fat content (Rose-Gottlieb method); P, crude protein content (Kjeldahl method); L, lactose (monohydrate, polarimetric method); SNF, solids non fat (gravimetric method). F, P, L and SNF were determined also by various indirect methods: - MIR (infrared (IR) technology with optical filters), 7 instruments in 4 labs; - MIR-FT (IR spectroscopy with Fourier's transformations), 10 in 6; - ultrasonic method (UM), 3 in 1; - Analysis by the blue and red box (BRB), 1 v 1. There were used 10 reference milk samples. Coefficient of determination (R2), correlation coefficient (r) and standard deviation of the mean of individual diff erences (MDsd, for n) were evaluated. All correlations (r; for all indirect and alternative methods and all milk components) were significant (P ≤ 0.001). MIR and MIR-FT (conventional) methods explained considerably higher proportion of the variability in reference results than the UM and BRB methods (alternative). All r average values (x minus 1.64 × sd for 95% confidence interval) can be used as standards for calibration quality evaluation (MIR, MIR-FT, UM and BRB): - for F 0.997, 0.997, 0.99 and 0.995; - for P 0.986, 0.981, 0.828 and 0.864; - for L 0.968, 0.871, 0.705 and 0.761; - for SNF 0.992, 0.993, 0.911 and 0.872. Similarly MDsd (x plus 1.64 × sd): - for F 0.071, 0.068, 0.132 and 0.101%; - for P 0.051, 0.054, 0.202 and 0.14%; - for L 0.037, 0.074, 0.113 and 0.11%; - for SNF 0.052, 0.068, 0.141 and 0.204.