|
|
 |
|
|
|
| DETERMINATION OF AMMONIA IN MILK AND CHEESE BY FOODLAB |
|
Ammonia is an important indicator of milk's hygienic quality, applicable in all phases of the production chain, reliable, simple and inexpensive. In fact, ammonia, as a metabolite of microbial activity, grows as the bacterial charge increases in the milk and it is not sensitive to thermal treatments, thus making it possible to monitor not only raw milk but also pasteurized milk.
Otherwise in the case of cheese the product being tested is placed in water so that the ammonia enters the watery solution and can be analysed by means of a few, simple operations which even non-specialised personnel can perform. With the FoodLab system, it is possible to determine the concentration of ammonia in whole or skim, raw or pasteurized milk in just a few minutes, 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 with a system that uses specific electrodes (reference method). |
|
| MATERIALS AND CORRELATION METHODS |
|
The FoodLab method is based on a colorimetric reaction in which the ammonia reacts with a phenolic derivative, forming a blue-green complex whose intensity, measured at 700 nm, is directly proportional to its concentration in the sample. The FoodLab instrument is capable of measuring the intensity of the color, eliminating the interferences due to milk's turbidity.
8 samples of whole milk and 8 samples of skim milk were tested with a system that uses specific electrodes (reference method). |
|
| RESULTS AND DISCUSSION |
|
The whole and skim milk values obtained by calibrating FoodLab with the milk samples tested using the reference method are shown in the figures (Fig.1 - skim milk and Fig.2 - whole milk). The regression line correlation coefficient (r > 0.99) indicates that the FoodLab system is in perfect agreement with the reference method.
The values obtained from the daily calibration of FoodLab are shown in the tables (Tab.1 - skim milk and Tab.2 - whole milk). The instrument aligns itself with the reference every day, maintaining r > 0.99. This guarantees the repeatability of the data as confirmed also by the standard deviation and by the VC computed for each reference sample. |
|
| Fig.1 - Correlation between FoodLab method and reference method – skim milk |
|
 |
|
| Fig.2 - Correlation between FoodLab method and reference method – whole milk: |
|
 |
|
| Tab 1 - Daily calibration with FoodLab system using known ¹ milk samples used to verify the accuracy. Skim milk |
|
Ref
ppM |
2,62 |
3,21 |
4,19 |
5,27 |
6,34 |
6,76 |
8,30 |
10,41 |
r |
| |
2,81 |
3,20 |
4,14 |
5,12 |
6,17 |
6,96 |
8,19 |
10,51 |
0,998 |
| |
2,84 |
3,24 |
4,40 |
5,37 |
6,46 |
7,32 |
8,84 |
10,87 |
0,998 |
| |
2,66 |
3,09 |
4,21 |
4,99 |
6,78 |
7,15 |
7,90 |
10,30 |
0,993 |
| |
2,62 |
3,11 |
4,24 |
5,20 |
6,33 |
7,13 |
8,12 |
10,35 |
0,998 |
|
|
|
|
|
|
|
|
|
|
MEAN |
2,73 |
3,16 |
4,25 |
5,17 |
6,43 |
7,13 |
8,26 |
10,50 |
|
SD |
0,10 |
0,06 |
0,09 |
0,14 |
0,22 |
0,13 |
0,35 |
0,22 |
|
CV,% |
3,5 |
1,9 |
2,2 |
2,7 |
3,5 |
1,9 |
4,3 |
2,1 |
|
| |
r Linear regression correlation coefficient computed on the values obtained by the automatic calibration of FoodLab
1 Frozen aliquots of known milk (reference method), thawed out every morning for calibration of the instrument. |
|
| Tab 2 - Daily calibration with FoodLab system using known ¹ milk samples used to verify the accuracy. Whole milk |
|
Ref
ppM |
2,59 |
3,05 |
4,56 |
5,77 |
6,76 |
8,30 |
11,29 |
14,76 |
r |
| |
2,68 |
3,21 |
4,49 |
5,47 |
6,75 |
8,14 |
12,03 |
14,33 |
0,996 |
| |
2,89 |
3,15 |
4,53 |
5,42 |
6,53 |
8,13 |
12,03 |
14,41 |
0,996 |
| |
2,75 |
3,15 |
4,61 |
5,62 |
6,65 |
8,23 |
11,86 |
14,62 |
0,998 |
| |
2,70 |
3,08 |
4,45 |
5,85 |
6,82 |
8,17 |
11,85 |
14,45 |
0,998 |
|
|
|
|
|
|
|
|
|
|
MEAN |
2,74 |
3,16 |
4,53 |
5,61 |
6,66 |
8,18 |
11,96 |
14,50 |
|
SD |
0,09 |
0,06 |
0,07 |
0,17 |
0,13 |
0,05 |
0,10 |
0,15 |
|
CV,% |
3,2 |
1,9 |
1,5 |
3,1 |
1,9 |
0,7 |
0,8 |
1,0 |
|
| |
r Linear regression correlation coefficient computed on the values obtained by the automatic calibration of FoodLab
1 Frozen aliquots of known milk (reference method), thawed out every morning for calibration of the instrument. |
|
|
| SHORT TABLE |
|
Linearity |
Accuracy |
Repeat. |
R2 |
Sensitivity |
Total
analysis
time |
Test/hour |
50 ppM |
± 2% |
CV < 4,5% |
r > 0,99 |
1 ppM |
8 - 12 min |
60 |
|
|
| |
|
|
 |
|
| Foodlab¬ |
|
|
» A new concept in quality analysis of food.
Foodlab is a quick, reliable and practical system for chemical tests on olive oil, seed oils, alimentary fats, vegetable purées, milk, cheese and other dairy products. |
|
| Application Sheet |
|
|
|
|
|
