Determination of extraneous water in milk samples, or the freezi

Chemistry: analytical and immunological testing – Food or dairy products – Dairy product

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Details

436 39, 436150, G01N 3306, G01N 3318

Patent

active

057390347

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The present invention relates to improvements in the determination of extraneous water in milk samples, or in the determination of the freezing point depression of milk samples.
Like the fat content of raw milk, any content of extraneous or added water is a quality parameter of the milk. However, unlike the fat content, the amount added or "extraneous" water in the raw milk may not exceed certain limited values, as higher contents than such values indicate a deficient management of the production or directly fraudulent addition of water to the raw milk. Thus, e.g., national Danish rules prescribe that a warning should be issued when the amount of added or extraneous water in raw milk exceeds 2% by weight, and that an excess of 4% of extraneous water gives rise to a penalty. For these reasons, determination of the amount of any extraneous water is an important determination in the quality control of milk.


DESCRIPTION OF THE RELATED ART

The conventional determination of extraneous water follows a program according to which a freezing point determination is performed at certain prescribed intervals. The freezing point depression of milk (relative to water) is directly related to the osmotic pressure in the milk, which is constant due to the biological processes involved in the cow's production of the milk. Thus, a reduction in the numeric value of the freezing point depression from a normal level indicates the presence of extraneous water, and the numeric size of the reduction is indicative of the amount of extraneous water in the milk. The determination of the freezing point depression is performed by means of a cryoscope in which the milk sample is cooled at a constant rate, and the temperature at which the freezing of the milk initiates is determined. This is a time-consuming process, and thus, there is a demand for a more efficient and fast method of determining the freezing point depression, or directly the amount of extraneous water in a milk sample.
The present invention provides a method in which the amount of extraneous water in a milk sample, or the freezing point depression of a milk sample, can be determined in a fast and efficient manner, using equipment of a type which is already acknowledged routine equipment in the quality control of milk.
"Routine testing of farm tank milk by infra-red analysis . . . ", J Koops et al, Neth. Milk Dairy J. 43 (1989), pp 3-16, discloses a method for the determination of the freezing point depression of milk by combining a measurement of the electric conductivity of the sample and a determination ("prediction") of the contents of lactose, fat and protein of the sample using a well-known infra-red analysing system.
In this reference, the determination of the freezing point depression of the sample is based on the concentrations of fat, lactose and protein such as these are determined in accordance with the infra-read analysis methods used. This has a number of limitations: Firstly, any minor component, such as citric acid or urea, is not included in the measurement, which can result in systematic errors because the effect of these minor components on the freezing point depression cannot be taken into consideration. Secondly, any random errors in the determination of the fat, lactose or protein may reappear with increased intensity in the prediction of the freezing point depression.


SUMMARY OF THE INVENTION

According to the present invention, it has been found that the determination of the freezing point depression by means of an infra-red analyzer can be improved by increasing the calibration leverage of the samples by including milk samples to which water has been deliberately added in the samples used for calibration of the infra-red analyzer, compared to the method of the above-mentioned reference according to which the calibration is performed using natural bulk milk samples. Also other methods of increasing the calibration leverage of the samples will improve the determination of the freezing point depression, such as explained i

REFERENCES:
Koops et al. (1989), Neth. Milk Dairy J. 43:3-16.
Janatsch et al. (1989), Anal. Chem. 61:2016-2023.
Martens et al. (1989), Norwegian Food Reserarch Institute, Multivariate Calibration, pp. 276-277.

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