Abstract: Whole milk solids are an important detection index for milk and yoghurt. The currently used measurement methods are GB5409-85 and GB / T5009146-2003 [1,2]. One is the calculation method, which is seldom used because of the complex fat measurement and high cost. The second is the weight loss method, which takes up to 4-5 hours, which is not suitable for the measurement of a large number of samples, nor is it practical for production. Big.
Yuan Xu et al. [3-5] used conventional laboratory conditions on the basis of GB5409-85, starting from strengthening the water evaporation process and accelerating the evaporation rate, using filter paper instead of sea sand to remove the water bath concentration process, drying once to constant weight Good results have been achieved. The measurement time is shortened from 5h to 115 ～ 2h in the past, which reduces the cost, and each batch can measure 10 samples at the same time. This article discusses the rapid determination of the solid content of whole milk in milk and yoghurt using the MB45 halogen moisture analyzer, aiming to establish a method with accurate, fast and convenient measurement results.
1. Materials and methods
1. Instruments
METTLER TOLEDO MB45 Halogen Moisture Analyzer (referred to as instrument).
2. Determination method
Weigh 215g of the well-mixed sample in an aluminum pan, and distribute the sample evenly with a medicine spoon. Under the optimal measurement conditions, perform the measurement according to the measurement procedure of the instrument.
3. Results and discussion
4. Selection of the best measurement conditions
The total solids content in milk and yoghurt is the quality of the sample after it loses moisture. In practice, what matters is the heating rate. When using a halogen lamp for heating, the maximum heating power can be reached in the shortest time, and the temperature can also rise quickly. In high temperature heating, the measurement conditions should be set according to different sample properties. For samples with more moisture content, the high temperature time can be extended appropriately, but the principle of ensuring that the sample should not be baked in the measurement. For samples with high sugar content, The high temperature time can be shortened appropriately. The best determination condition of the whole milk solids in the selected milk and yoghurt after several times of testing in a ladder mode is: 190 ℃ 3min → 120 ℃ 5min → 105 ℃ to constant weight.
2. Comparison of instrument method and national standard method
For 11 milk samples and 10 yogurt samples, the whole milk solids were measured by the instrument method and the national standard method (GB / T5009146-2003). The results are shown in Table 1. After t test, t (yogurt) = 11346, t (0105, 9) = 21262, P> 0105; t (milk) = 11299, t (0105, 10) = 21228, P> 0105, there is no statistics between the two methods Learn the differences. It shows that using the instrument to determine the solid content of whole milk in milk and yogurt can replace the national standard method.
1. Precision measurement
Take a sample of milk and yoghurt each for 7 measurements. The RSD of milk and yoghurt were 0182% and 1150% respectively.
2. Uncertainty evaluation of instrumental measurement of whole milk solids
The measurement results in Table 2 are used to evaluate the measurement uncertainty of the whole milk solids measured by the instrument in milk and yogurt. Take k = 2, milk whole milk solids: U = (10185 ± 0107) g / 100g; yogurt whole milk solids: U = (21132 ± 0124) g / 100g.
3. Measurement time comparison
The MB45 type halogen moisture analyzer for measuring the whole milk solids of milk and yogurt is obviously better than the national standard method in the measurement time. When measuring the total milk solids of milk and yoghurt by the national standard method, first empty the dish with a constant weight, and then weigh the sample to evaporate the water and put it in a drying cabinet to bake to a constant weight. A sample can be completed at least 8 to 12 hours. The MB45 Halogen Moisture Analyzer integrates weighing and baking, with a fast heating rate, which greatly shortens the measurement time. In the determination of total solids of 10 parts of yogurt and 11 parts of milk, the maximum time is only 13 minutes.
In summary, the use of MB45 halogen moisture analyzer to determine the total milk solids in milk and dairy products can shorten the test time by setting different automatic test endpoints, thereby greatly improving work efficiency.
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