Fast detection technology IV for adulteration of t

Rapid detection technology for adulteration of fresh milk (IV)

9 how to distinguish between mixed milk of cattle and sheep

milk is expensive and sheep's milk is cheap, so dairy merchants often mix sheep's milk into milk to make profits. So, how should we quality control personnel correctly distinguish this part of mixed milk? We think the way is to add acidity, salt and taste

9.1 beating acid

9.1.1 principle

the titration acidity of milk is generally 14~18ot, and the acidity of sheep's milk is 9~15ot. Use 70 ℃ beating acid alcohol to test, and the milk mixed with sheep's milk tends to stick to the tube

9.1.2 reagent 1 generally, the preparation of acid reagent is only used in structural component experiments or simple material performance experiments: add an appropriate amount of bromothymol blue to the prepared 70 degree alcohol, so that the alcohol reagent just changes from blue to yellow

9.1.3 operation method

take 2 ml of acid reagent into the test tube, then add 2 ml of milk sample, shake well and observe

9.1.4 conclusion judgment

under the condition of normal titration acidity, if there is tube sticking phenomenon, it indicates that the milk is mixed with goat milk, otherwise, it can be regarded as pure fresh milk

9.2 measuring salt (chloride)

9.2.1 principle

the chloride content in milk is generally less than 0.15%, while that in sheep's milk is usually less than 0.18%, but higher than that in milk. If sheep milk is added to cattle, the chloride content of mixed milk will be greater than 0.15%

k2cro4+2agno3 → agco4 ↓ +2kno3

red

agcro4+2naci → 2agci ↓ +na2co4

white

9.2.2 reagent

10% potassium chromate solution; AgNO3 solution of 0.05634n (calibrated with standard NaCI Solution of the same concentration)

9.2.3 operation method

take 2 ml of milk sample into the test tube, add 5 drops of high-performance modified plastics such as PC and peek, which are significantly used in electronic appliances. Use 10% potassium chromate solution, titrate with 0.05634n AgNO3 until the milk sample turns from yellow to red, and record the consumed ml

9.2.4 conclusion judgment

if the number of ML consumed is greater than 1.5, it can be regarded as abnormal milk

9.2.5 description

(1) salt test can directly explain whether milk is mixed with salt. If you want to determine whether milk is mixed with goat milk, you must do it at the same time with acid test to determine the nature

(2) as the chloride content in fresh milk is greatly affected by season and feed, dairy enterprises can appropriately relax this standard in summer

(3 ordinary ball screws) goat milk has a smell of mutton, and the smell of cow sheep mixed milk is also obvious

10 test urea

10.1 objective

because most dairy manufacturers often take protein as the main detection index when implementing "price according to quality" for raw milk, some illegal dairy merchants often add urea to fresh milk to improve the protein content. The purpose of urea measurement is to find out and reject this part of abnormal milk

10.2 test method: Grice reagent method

10.2.1 principle

urea reacts with nitrite in acid solution to generate carbon dioxide gas to escape, while nitrite can react with Grice reagent to generate purplish red dye, and the addition of urea will affect the occurrence of this reaction

10.2.2 reagent

(1) preparation of Grice reagent: weigh 89g tartaric acid, 10g p-Aminobenzene Sulfonic Acid and 1g α- Naphthylamine, grind in a mortar and mix well, then put it into a brown bottle for standby

(2) concentrated sulfuric acid

(3) 0.05% sodium nitrite solution: weigh 50mg sodium nitrite and dissolve it in 100ml distilled water, and put it in a brown bottle for storage

10.2.3 operation method

take 3ml of the tested sample milk and put it into a large test tube, add 0.5ml of 0.05% sodium nitrite solution, add 1ml of concentrated sulfuric acid, tightly cover the rubber stopper and shake it well, and add about 0.1g Grice reagent to the test tube after the foam disappears. Shake well and observe the results after 25 minutes

10.2.4 judgment conclusion

judgment conclusion according to the color change of milk sample (see Table 9)

Table 9 comparison table of color change of milk sample and judgment conclusion

judgment conclusion of milk color adulteration test

purplish red qualified milk without urea

non discoloration abnormal milk with urea

10.2.5 description

the sensitivity of this method is 0.01%. Therefore, the tested milk should not be less than 2.5ml at least. This test is best compared with normal milk, and its results will be more accurate

11 measure hydrolyzed animal protein powder (also known as new dairy special protein powder)

11.1 objective

dairy enterprises price by protein content. Some dairy farmers add hydrolyzed protein powder to raw milk in order to mix water without reducing protein content, and at the same time, improve the content of dry matter

11.2 detection method

11.2.1 principle

use mercury nitrate precipitation method to remove casein, but the hydrolyzed protein will not be removed, and there will be precipitation reaction with saturated picric acid solution

11.2.2 reagent preparation

(1) remove 14g of protein reagent mercury nitrate, add

100 ml of distilled water, add 2.5 ml of concentrated nitric acid, heat it to help dissolve, and add distilled water to 500 ml after all the reagents are dissolved

(2) saturated picric acid weigh 3 g of picric acid and add 200ml of

distilled water

11.2.3 operation method

take 5ml of milk sample, add 5ml of deproteinizing reagent, mix evenly, filter, and slowly add about 0.6ml of saturated picric acid solution along the filtrate tube wall to form a circular contact surface

11. That is to say, judging by the result of 2.4 of this design

judging by the color change of the ring layer (see table 10)

table 10 comparison table of ring layer color changes and judgment results

judgment conclusion of ring layer color adulteration test

clear qualified milk without hydrolyzed animal protein

white ring abnormal milk with hydrolyzed animal protein

11.2.5 description

(1) hydrolyzed protein powder is processed and refined from waste leather, hair and other waste materials, and it is not edible at all, Moreover, the content of heavy metals and carcinogens such as nitrite is high. Long term consumption of milk or milk powder containing hydrolyzed protein powder will cause great harm to human body

(2) the more hydrolyzed animal protein powder is mixed in the raw milk, the more obvious the white ring in this test

(3) the minimum detectable amount of this test is 0.05%

(4) the white ring phenomenon is not obvious in the test with milk samples frozen for a long time (10hr), and the reason needs further research and discussion