Fast detection technology II for adulteration of t

2022-08-13
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Rapid detection technology for adulteration of fresh milk (II)

3.3 detection method of nitrate

3.3.1 principle

after nitrate in fresh milk is reduced to nitrite, it reacts with p-Aminobenzene Sulfonic Acid and methylnaphthylamine to form red azo compounds

3.3.2 reagent

a, reducing agent

44g barium nitrate, 5g manganese sulfate, 2G cadmium acetate,

2G zinc powder. After drying, mix them together, grind them into fine powder, and store them in brown advertising bottle for standby

b, display agent

is the same as the reagent for nitrite determination

3.3.3 operation method

take 2ml of milk sample into a small test tube, add a small spoon of reducing agent (about 0.3 g), shake well, add 2ml of chromogenic agent, shake well for about 3 minutes, and then observe

3.3.4 result determination

determine the result according to the color depth (see Table 3)

Table 3 comparison table of milk sample color and conclusion judgment

conclusion judgment of nitrite or nitrate content in milk sample color

milky white no nitrite or nitrate qualified milk

micro pink containing nitrite or nitrate 0.2mg/front pin puller seat kg abnormal milk

water pink containing nitrite or nitrate 0.3mg/kg abnormal milk

pink containing nitrite or nitrate 0.4mg/kg serious abnormal milk

Red containing nitrite Acid salt or nitrate ≥ 0.5mg/kg serious abnormal milk

3.3.5 description

(1) the nitrate content in fresh milk can be determined by doing

at the same time with nitrite determination method

(2) as a dairy manufacturer, this method has the advantages of convenience, speed and accuracy in controlling the quality of fresh milk purchase. When purchasing fresh milk, as long as nitrate is measured, the content of nitrate and nitrite in fresh milk can be controlled, so as to effectively ensure the quality of fresh milk purchase

(3) when low desalted whey powder is mixed into fresh milk, sometimes

will also aggravate the phenomenon of this experiment

4 measuring glucose substances

4.1 purpose

the ring stiffness testing machine here is mainly used to test the mechanical properties of the ring stiffness of rigid cement pipes. The substances containing glucose include glucose powder, Glycone, dextrin and fat powder, which can be used for various parts in the aircraft Fat powder, etc. In order to improve the density, fat, protein and other physical and chemical indicators of fresh milk, dairy farmers often mix this kind of substance into fresh milk. Therefore, it is very necessary to detect this kind of substance

4.2 detection method

4.2.1 principle

glucose in varying amounts is found in glucose powder, dextrin, fat powder and vegetable fat powder

4.2.2 reagent

medical urine sugar test paper (sold in major pharmaceutical stores)

4.2.3 operation method and judgment

take the urine sugar test paper, immerse it in the milk sample for 2 seconds, take it out, and compare it with the standard plate within 2 minutes to observe the phenomenon. When there are substances containing glucose, the test paper will change color

5 measure starch, soymilk, flour and other substances

5.1 objective

dairy farmers add such substances to fresh milk purely to increase the weight and density of milk. Because Coke tube phenomenon often occurs in the concentration process of such substances, the quality must be strictly controlled

5.2 detection method

5.2.1 principle

iodine turns blue when encountering starch

5.2.2 reagent preparation

starch reagent: 10g iodine and 40g potassium iodide are dissolved in 500ml distilled water

5.2.3 operation method and judgment

take 3ml of milk sample into the test tube, add 1 drop of starch reagent and shake well to observe the phenomenon. In the presence of starch, the milk sample appears blue

5.3 shows that

the sensitivity of this experiment is higher when the milk sample cooled after the heating boiling test is used

6 about whey powder

at present, China has revised and improved the quality system documents such as the quality manual and the Cheng Xu document before and after. All whey powder seen in the market depends on imports. Whey powder is a by-product of cheese extracted from fresh milk by foreign dairy enterprises. Therefore, the price is much cheaper than whole milk powder, which also makes it possible for some illegal dairy merchants to mix whey powder when selling fresh milk. Because all components of whey powder come from fresh milk, it is difficult to distinguish the authenticity of the milk by conventional chemical methods. However, since the fat content of whey powder is generally ≤ 1.2%, the protein content is ≤ 12%, and the lactose content is ≥ 75%, we can quickly determine its physical and chemical indicators with the help of milk composition analyzer, and purchase it by "pricing by quality" or "deducting the corresponding proportion". We have confirmed through experiments that when the density of fresh milk remains unchanged, the fat content will decrease by 0.1 percentage points, the protein content will decrease by 0.05 percentage points, and the adulteration rate of whey powder of fresh milk is more than 3%. If the factor of increasing the density of milk is added, the adulteration rate will be higher. In production, we also found that the fat content of some fresh milk mixed with whey powder is even lower than the protein content. At this time, the lactose content in fresh milk is measured again. If lactose ≥ 4.80%, it can be determined that the raw milk is mixed with whey powder

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