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| DETERMINATION OF UREA IN MILK BY FOODLAB |
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| The urea content in raw milk is in relation to the amount of protein in the animal's diet and thus it makes it possible to define a proper diet. Furthermore, with this test it is possible to detect any additions of urea to the milk for the purpose of increasing its total nitrogen content.
With the FoodLab system, it is possible to determine the concentration of urea in just a few minutes in whole or skim, raw or pasteurized milk, without any previous treatment of the sample.
Furthermore, the FoodLab analyzer, using previously dispensed, non-returnable (disposable) cuvettes, requires neither specialized personnel nor reagent preparation.
The method's reliability and precision are guaranteed by a calibration system that makes it possible to align the instrument using known milk samples.
The FoodLab system was compared to the classic method of treatment of the sample through precipitation and centrifugation.
The analytical method and the instrument were subjected to evaluation tests at the Laboratorio Standard Latte (Milk Standard Laboratory) of the Associazione Italiana Allevatori (Italian Breeders Association). |
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| MATERIALS AND CORRELATION METHODS |
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| The FoodLab method is based on a colorimetric reaction in which urea is transformed into ammonia by the urease, which reacts with a phenolic derivative, forming a blue-green complex whose intensity, measured at 700 nm, is directly proportional to the concentration in the sample. The small amounts used make the test independent of the type of milk (skim or whole).
A milk sample was centrifuged with a precipitate: the supernatant solution was tested with the spectrophotometer and titrated with an aqueous standard (reference method). The same milk, untreated, was tested with FoodLab.
Recovery tests were carried out on this, by now, known milk: 5 ml of a standard solution of urea in various concentrations were added to 3 milk samples, which were then tested using FoodLab.
Five (5) repeatability tests were also carried out for each sample. |
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| RESULTS AND DISCUSSION |
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| The FoodLab system allows a practically total recovery of urea, both of the milk tested with the reference method (28 mg/dL) and of the samples to which the standard solution was added. The reference values and the tests carried out using the FoodLab system are compared in Tab.1. The values are perfectly comparable and the repeatability of the data is very good, as seen from the standard deviation and from the VC computed for each sample. In Fig. 1, the regression line correlation coefficient (r = 0.999) confirms the optimum agreement of the instrument with the reference method. |
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| Fig.1 - Correlation between FoodLab method and standard values |
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| Tab 1 - Daily calibration with FoodLab system using known milk samples used to verify the accuracy |
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Ref
mg/dL |
19,8 |
20,6 |
22,1 |
22,9 |
23,4 |
24,2 |
24,7 |
25,5 |
27,5 |
38,3 |
r |
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19,7 |
20,5 |
22,5 |
23,2 |
23,3 |
23,7 |
24,5 |
25,7 |
27,5 |
37,5 |
0,998 |
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19,5 |
20,0 |
21,9 |
22,8 |
23,6 |
24,5 |
24,3 |
25,8 |
27,2 |
37,9 |
0,998 |
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19,8 |
20,9 |
22,7 |
23,5 |
23,4 |
24,3 |
24,8 |
25,0 |
27,6 |
38,5 |
0,997 |
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19,9 |
20,3 |
22,6 |
22,9 |
23,8 |
23,6 |
24,9 |
25,6 |
27,9 |
38,2 |
0,997 |
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MEAN |
19,6 |
20,5 |
22,4 |
23,1 |
23,4 |
23,9 |
24,5 |
25,6 |
27,5 |
38,2 |
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SD |
0,28 |
0,34 |
0,32 |
0,27 |
0,28 |
0,45 |
0,31 |
0,39 |
0,25 |
0,48 |
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CV,% |
1,4 |
1,6 |
1,4 |
1,2 |
1,2 |
1,9 |
1,3 |
1,5 |
0,9 |
1,2 |
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r Linear regression correlation coefficient computed on the values obtained by the automatic calibration of FoodLab |
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| SHORT TABLE |
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Linearity |
Accuracy |
Repeat. |
R2 |
Sensitivity |
Total
analysis
time |
Test/hour |
100 mg/dL |
± 1% |
CV < 1% |
r > 0,99 |
5 mg/dL |
8 - 14 min |
60 |
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