Result interpretation of experimental calibration for milk citric acid determination via infra-red spectroscopy (MIR-FT)

Abstract

Citric acid (KC) in milk is indicator of cow energy metabolism. Milk laboratories set up KC determination. A method can be infra-red analyse (MIR-FT). The goal was to develop a relevant method for reference sample preparation for MIR-FT (indirect method, Lactoscope FTIR and MilkoScan FT 6000) calibration. As reference was used a photometric method (c; 428 nm). KC was added (n = 3) into some re­fe­ren­ce milk samples (n = 10, bulk milk). Mean value was 9.220 ± 3.094 mmol . l−1 with variation range from 6.206 to 15.975 mmol . l−1. Recovery c was from 100.8 to 120.2 %. Correlation between c and ­MIR-FT were from 0.979 to 0.992 (P < 0.001). These were lower in the set of native milk samples (n = 7), from 0.751 (Lactoscope FTIR; P < 0.05) to 0.947 (MilkoScan FT 6000; P < 0.001) in comparison to original va­lues from 0.981 to 0.992 (n = 10; P < 0.001). Correlations between calibrated MIR-FT instruments were from 0.958 to 1.0 (P < 0.001). Average recovery for instruments (n = 12) was 101.6 ± 18.1 %. The mean differences between c method and MIR-FT after calibration (n = 4) moved from −0.001 across zero to 0.037 %. Standard deviation of differences was from 0.0074 to 0.0187 % at MilkoScan FT 6000 and from 0.0105 to 0.0117 % for Lactoscope FTIR. Relative variability of differences (MIR-F (filter technology) and FT) for major components fat (T), proteins (B) and lactose (L) in total and minor components KC and free fatty acids (VMK) was estimated to 1.0 and 7.2 and 34.4 %. The KC result is inferior than T, B and L superior than VMK. Autocorrelation (0.042; P > 0.05) of results demonstrated the in­de­pen­den­ce of consecutive measurements. Milk preservation effect amounted 0.2323 (P < 0.001) with bronopol and 0.0339 (P > 0.05) mmol . l−1 with dichromate. It was (3.0 and 0.44 %) practically negligible, redeemable via relevant calibration. The results of proficiency testing in post-calibration period and evaluation of double transport stress effect samples (difference was −0.006 ± 0.071 mmol . l−1 (P > 0.05)) demonstrated the useability for central calibration system. Milk KC results of MIR-FT calibration were good and can be suitable for practical screening.

Comparison of Fatty Acid Proportions Determined by Mid-Infrared Spectroscopy and Gas Chromatography in Bulk and Individual Milk Samples

“…These analyzers are used in dairy laboratories with different types of modifications according to the analytical techniques of the manufacturers (Foss Electric from Denmark, Bentley Instruments from the USA, Delta Instruments from the Netherlands, and others). Recently, in addition to the basic components [ 2 , 7 ] of milk (fat, protein, casein, lactose, total solids, solids-non-fat), the analysis spectrum has been expanding, primarily with undesirable metabolites (citric acid, free fatty acids (FAs)), ketones (acetone, beta-hydroxybutyric acid), urea [ 5 , 10 , 11 , 12 , 13 , 14 ], and other components in milk, especially the milk FA proportion (MFAP) [ 3 , 15 , 16 , 17 ]. The monitoring of the above-listed milk components and metabolites serve to control the health, breeding, nutrition, and reproduction of cows as well as the quality of their milk [ 5 , 12 , 16 , 18 , 19 , 20 , 21 , 22 ].…”