4 Measuring glucose substances
4.1 Purpose The common glucose-containing substances include glucose powder, glycolene, dextrin, fat powder, and non-dairy creamer. In order to increase the density and the physical and chemical indexes of fats and proteins, dairy farmers often incorporate such substances into fresh milk. Therefore, it is necessary to detect such substances.
4.2 Test Methods
4.2.1 Principle Glucose powder, dextrin, fat powder, and non-dairy creamer have different levels of glucose.
4.2.2 Reagents Medical urine test strips (all major pharmaceutical stores have sales).
4.2.3 Operation method and determination Take the urine test paper and dip it into the milk sample for 2 seconds. Take out the control plate within 2 minutes and observe the phenomenon. In the presence of glucose-containing substances, the test paper changes color.
5 Measure starch, soymilk and flour
5.1 The target dairy farmer mixes these substances with fresh milk purely to increase milk weight and increase density. Because this kind of substance often causes the phenomenon of the coke tube in the thickening craft, must strictly control the quality.
5.2 Test Methods
5.2.1 Principle Iodized starch turns blue.
5.2.2 Reagent preparation Starch reagent: 10g of iodine and 40g of potassium iodide were dissolved in 500mL of distilled water.
5.2.3 Operation method and determination Take 3mL of milk sample in the Test Tube , add 1 drop of starch reagent and shake to observe the phenomenon. In the presence of starch, milk samples appear blue.
5.3 shows that this experiment uses a boiled milk sample after the heating boil test to be more sensitive.
6 About whey powder At present, whey powder seen on the domestic market in China is all dependent on imports. Whey powder is a by-product of the extraction of cheese from fresh milk by foreign dairy companies. Therefore, the price is much lower than that of whole milk powder. This also makes it possible for some unscrupulous milk traders to incorporate milk powder in the sale of fresh milk. Because all the components of whey powder are derived from fresh milk, it is difficult to distinguish between true and false milk using conventional chemical methods. However, because the fat content of whey powder is generally ≤1.2%, the protein content is ≤12%, and the lactose content is ≥75%. Therefore, we can use the milk composition analyzer to quickly determine its physicochemical indexes to “price according to quality. "Or deduct a corresponding proportion" to acquire. Through experiments, we have verified that when the density of fresh milk is constant, each 0.1% decrease in fat content, the protein content will decrease by 0.05%, and the adulteration rate of whey powder in fresh milk will be above 3%. Raising the density factor of milk, this adulteration rate will be even higher. In production, we also found that some of the fresh milk with whey powder is even lower than the protein content. At this time, the lactose content in fresh milk is measured. If the lactose is ≥ 4.80%, the raw milk can be determined. Mixed with whey powder.
7 Antibiotics
7.1 Objectives Antibiotics in fresh milk are caused by drug residues in breast milk secreted by certain diseased cows after drug treatment. Antibiotic testing is a mandatory item for dairy companies to produce fermented yogurt. Nowadays, some domestic large-scale dairy enterprises have also conducted antibiotic tests on milk during the production of milk powder to produce anti-milk powder, so as to avoid the occurrence of allergic reactions among very few consumers. Drinking milk containing antibiotics for a long time, the bacteria in the human body will produce resistance. Since the residual amount of antibiotics is generally below several PPbs, it is difficult to detect it in a short time using general chemical instruments and equipment. Here's a simple way to introduce antibiotic testing to our factory.
7.2 Detection method (fermentation method)
7.2.1 Principles Antibiotics affect the normal fermentation of fresh milk.
7.2.2 Instruments and bacteria
250mL flask; lactic acid bacteria species.
7.2.3 Operation method Take 150mL of milk sample in a 250mL flask, heat and boil in an electric furnace, cool to 42°C, add 15mL of inoculated Lactobacillus species, and then ferment in a 42°C incubator for 1 hour. After observation.
7.2.4 Conclusions Judgment If the milk sample has been fermented, it proves to be free of antibiotics; otherwise it is abnormal milk.
7.3 Test Method (Improved Fermentation Method)
In order to facilitate the examiner's observation of the phenomenon of fermentation, some people use the indicator in the test milk, because the production of lactic acid fermentation lactic acid bacteria will reduce the PH value of the solution, the color change of the indicator to determine whether the test milk fermentation, to determine whether the test There are antibiotics or preservatives.
7.3.1 Principles Antibiotics and preservatives can inhibit the growth and reproduction of lactic acid bacteria, do not change the pH of milk, thereby preventing the rancidity of raw milk, and of course do not change the alkaline indicator litmus solution before adding it to the test milk. colour.
7.3.2 Reagents and strains (1) 0.5 N sodium hydroxide solution: Weigh 2.0 g of pure chemical sodium hydroxide in 100 mL of distilled water.
(2) Litmus reagent: 5% litle aqueous solution.
(3) Lactic acid bacteria strains.
7.3.3 How to operate
a. Take 10 mL of tested milk into a large test tube and add 2 mL of litmus reagent.
b. Using a dropper, carefully instill 0.5N sodium hydroxide solution to make the tested milk show a distinct blue color.
c, will be tested with milk plugs plug mouth in 85 °C
Water Bath pot for 10 minutes, cooling.
d, adding lactic acid bacteria seed liquid 1m, after mixing, placed in a constant temperature incubator at 42 °C fermentation.
7.3.4 Conclusions Judgment results of color change in milk samples (see Table 4)
Table 4 Comparison of milk color and judgment results
Milk color
Adulteration test
Decision conclusion
Blue unchanged
Contains antibiotics or preservatives
Abnormal milk
red
Does not contain antibiotics or preservatives
Qualified milk
7.3.5 Description: In order to save the determination time, it is best to do a control experiment at the same time.
8 Preservatives Adding preservatives to fresh milk can cause damage to the nutrients in the milk, as well as adverse effects on the mouthfeel of dairy products. Some even interfere with our adulteration inspections, such as sodium metabisulfite. Here are two simple methods for the detection of two preservatives that have a major impact on our inspection work.
8.1 Measuring Hydrogen Peroxide (H2O2)
8.1.1 Principle Hydrogen peroxide (H2O2) has strong oxidizing properties. It can oxidize iodide (I-) in potassium iodide (I-) to iodine (I2). Since iodine meets starch in blue, we can quickly detect the addition. Hydrogen peroxide milk samples.
8.1.2 Drugs and reagents Potassium iodide (analytically pure); 1% starch solution.
8.1.3 Operation method Take 3 mL of milk sample in a test tube, add 1 tsp of potassium iodide (about 0.3 g), shake well, and then drop 2 drops of 1% starch solution. Shake well and observe the phenomenon.
8.1.4 Judgment results are determined by the color change of milk sample (see Table 5)
Table 5 Comparison of color and judgment results of milk samples
Milk color
Adulteration test
Conclusion judgment
Does not change color
No preservatives
Qualified milk
blue
Contains preservatives
Abnormal milk
8.2 Measuring Hydrogen Peroxide (H2O2): Hydrogen peroxide added to milk of vanadic acid coloration method will decompose into water and oxygen after a period of time. Therefore, it is not easy to detect if the amount of hydrogen peroxide added is not large or the time is too long. The minimum detection concentration of hydrogen peroxide in this method is 0.01%.
8.2.1 Principle Hydrogen peroxide reacts with vanadic acid reagents to form red substances.
8.2.2 Reagents
1% vanadate, sulfuric acid solution: Dissolve 1 g of vanadic acid in 100 mL of 20% sulfuric acid solution.
8.2.3 Operation method Take 2mL of milk sample in a test tube and add 5 drops of 1% vanadic acid reagent. Shake well and observe the phenomenon.
8.2.4 Judgment results are judged by the color change of milk samples (see Table 6)
Table 6 Comparison of milk color and judgment conclusion
Milk color
Adulteration test
Decision conclusion
Does not change color
Does not contain H2O2
Qualified milk
red
With H2O2
Abnormal milk
8.3 measuring sodium metabisulfite (Na2S2O5)
8.3.1 Principles Sodium metabisulphite has a strong reducing and bleaching action. It can reduce iodine (I2) to iodide (I-), thus losing iodine's ability to turn blue.
8.3.2 Reagent preparation (1) Starch reagent: 10g iodine plus 20g potassium iodide in 500 mL distilled water;
(2) 1% starch solution: 1 g of starch is dissolved in 100 mL of distilled water (dissolved if necessary).
8.3.3 Method of operation Take 3 mL of milk sample in a test tube, add 1 drop of starch reagent, shake and shake for 3-5 seconds, add 2 drops of 1% starch solution, shake and shake to observe the phenomenon.
8.3.4 Judgment results are judged by the color change of milk samples (see Table 7)
Table 7 Comparison of milk color and judgment results
Milk color
Adulteration test
Conclusion judgment
blue
No preservatives
Qualified milk
white
Contains preservatives
Abnormal milk
8.3.5 Precaution The milk samples that have been subjected to a starch test after heating cannot be used in this test.
8.3.6 Description (1) The minimum detection of sodium sulfite by this method is 0.01%.
(2)Sodium metabisulphite is the most prevalent antiseptic that we currently find and interferes with adulteration tests. It contains alkali, nitrite, nitrate, glucose, dextrin, fat powder, non-dairy creamer, starch, and soy milk. Examinations such as soups and soups have great interference, and it is easy for fresh milk containing these substances to escape our surveillance. It is recommended that peers use it as a daily check item.
8.4 Formaldehyde (Commercial product called formalin)
8.4.1 using concentrated sulfuric acid method
8.4.2 Operation method Take 2mL of milk sample in the test tube, add concentrated sulfuric acid 2mL slowly along the tube wall, make the milk sample and mixture into two layers, observe the phenomenon.
8.4.3 The result is judged by ring color judgment result (see Table 8)
Table 8 Comparison of Color and Determination Results of Milk Sample and Sulfuric Acid Junction Layer
Ring color
Conclusion judgment
Fawn
Qualified milk
Purple ring
Abnormal milk
8.4.4
(1) The method is slow to measure formaldehyde plus sulfuric acid, otherwise the color of the ring layer is not easy to judge.
(2) It is best to do a blank control experiment at the same time to facilitate quick and accurate determination.
(3) Some non-environmentally friendly paints or powders also contain formaldehyde or its derivatives. If an unscrupulous dairy company incorporates this kind of paint into fresh milk, it will cause abnormalities.
(4) Formaldehyde is a carcinogenic substance that is toxic to the human body. It is recommended that dairy manufacturers use it as a mandatory inspection item in summer.
9 How to distinguish cows, sheep and dairy cows from high milk prices and cheaper sheep milk, so dairy companies often incorporate goat milk in their milk for profit. So, how can our quality control personnel correctly distinguish this part of mixed milk? We believe that the approach is to fight acid, salt to measure and taste to taste.
9.1 acid
9.1.1 Principle Milk titration acidity is generally 14 ~ 18oT, sheep lactate is 9 ~ 15oT, with 70 degrees of sour alcohol to test, milk mixed with goat milk is often the phenomenon of tube.
9.1.2 Reagent Preparation Acidic Reagents: Add appropriate amount of bromine thymol blue in the prepared 70-degree alcohol, so that the alcohol reagent can just turn from blue to yellow.
9.1.3 Method of operation Take 2 mL of acid reagent in test tube, then add 2 mL of milk sample. Shake well and observe.
9.1.4 Conclusions In the case of a normal titration acidity, if there is a sticking phenomenon, the milk is mixed with goat milk. Otherwise, it can be regarded as pure fresh milk.
9.2 Salt Measurement (Chloride)
9.2.1 Principles Chloride content in milk is generally less than 0.15%, while goat milk is usually less than 0.18%, but higher than cow's milk. If cows are mixed with goat milk, the chloride content of the blended milk will be greater than 0.15%.
K2CrO4+2AgNO3→AgCO4↓+2KNO3
red
AgCrO4+2NaCI→2AgCI↓+Na2CO4
white
9.2.2 Reagents
10% potassium chromate solution; 0.05634N AgNO3 solution (calibration with the same concentration of standard NaCI solution).
9.2.3 Operation method Take 2 mL of milk sample in a test tube, add 5 drops of 10% potassium chromate solution, titrate with 0.05634N of AgNO3 until the milk sample changes from yellow to red, and record the consumed milliliters.
9.2.4 Conclusions Judging If the number of milliliters consumed is greater than 1.5, it may be considered abnormal milk.
9.2.5 Description (1) The salt test can directly explain whether salt is incorporated in milk. If it is to be judged whether sheep milk is mixed, it must be done together with the acid test in order to qualify.
(2) Since the content of chloride in fresh milk is greatly affected by the season and feed, dairy companies may relax this standard in the summertime.
(3) Goat milk has a savory taste, and this kind of taste is more obvious in cattle and sheep's mixed milk.
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