A/s Foss Electric

Lars Nygaard

Torben Lapp

Borkur Arnvidarson

Niels Brems

Steen K Andersen

Bokur Arnvidarson

Lars-Ove Sjaunja

An infrared attenuation measuring system, for the quantitative determination of the concentration of one or more components in an aqueous fat-containing sample, such as milk, by an infrared attenuation technique. The system comprising a set of waveband-related parameters containing information enabling the system to calculate the concentrations substantially independent of the degree of homogenization of the fat-containing sample, and/or to determine the degree of homogenization of the sample. The parameter set contains parameters which are related to wavebands containing a high degree of information about the homogenization degree of the sample. This may be wavebands containing little information about the chemical components of the sample, and/or wavebands containing a substantial amount of information about the chemical components of the sample. The system is calibrated with aqueous fat-containing samples with different degrees of homogenization. The calculating means may be a microprocessor calculating the concentration of the component or components in question, or a neural network defined by the wave band-related parameters. The wavebands in which the attenuation values are determined in the infrared attenuation measuring means may be defined by optical filters, stationary grating and movable and/or multiple detectors, or by movable grating and one or several stationary or movable detectors. The infrared attenuation measuring means may comprise an interferometer, the data obtained from the interferometer being processed using Fourier transformation; and infrared attenuation measuring means of this type may be a FTIR spectrophotometer.

Infrared attenuation measuring system

The concentration of urea in a concentration range of 0-0.1% in a milk sample containing at least 1% fat, at least 1% dissolved lactose, and at least 1% protein, is determined with an accuracy better than 0.007%, expressed as Standard Error of Prediction, by an infrared attenuation measuring technique, by determining, on the sample, the attenuation in the region of infrared radiation from 1000 cm.sup.-1 (10.0 .mu.m) to 4000 cm.sup.-1 (2.50 .mu.m), at least one determination being made in a waveband in the region from 1000 cm.sup.-1 (10.0 .mu.m) to 1800 cm.sup.-1 (5.56 .mu.m) in which urea absorbs, at least one other determination being made in a waveband in which fat absorbs, at least one further determination being made in a waveband where lactose absorbs, and at least one further determination being made in a waveband where protein absorbs; determining, on the basis of the thus determined attenuations and predetermined parameters established by multivariate calibration, the contribution from fat, lactose, and protein in the waveband where urea absorbs, and quantitatively assessing the concentration of urea in the sample on the basis of the absorption in the waveband where urea absorbs, and on the basis of the determined contribution from fat, lactose and protein in said waveband. The multivariate calibration may be performed by a Partial Least Squares algorithm, Principal Component Regression, Multiple Linear Regression, or Artificial Neural Network learning. Using the method according to the invention, compensation for the influence on the urea measurement may further be performed for one or several of the following components: citric acid, free fatty acids, antibiotics, phosphates, somatic cells, bacteria, preservatives and casein.

Method of determining urea in milk

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Gr sted, Denmark

Lars Nygaard