Note:                                                                    

                In these notes contains some important testes in milk and milk products. Based on the answers candidates need to generate their question yourself. It will improve your mind concentration and confidence.

MILK

1. Most common preservative used in Milk products for store the test samples is Formalin.
2. How much amount of Formalin is used to preserve the milk 0.4% Formalin.
3. Seliwanoff’s test is used to detect the disaccharides in food.
4. Seliwanoff’s reagent is Resorcinol in hydrochloric acid
5. Seliwanoff’s test is used to identify sucrose adulteration in milk
6. The cheery red colour shows the Postivie Seliwanoff’s test.
7. The product form from fructose (a keto sugar) is 5- Hydroxymethylfurfural condense with resorcinol to form cherry red colour.
8. A keto sugar is more actively attacks resorcinol compare than aldehyde group.
9. The iodine test is used to detect the starch in milk.
10. Starch reacts with iodine to form blue colour.
11. The development of blue colour is due to complex formation between iodine and amylose component of starch.
12. The formation of red purple colour in starch test is complex formation between iodine and amylopectin.
13. The iodine test is more active in acidic medium.
14. The blue colour developes in iodine test is disappears above a pH of 9.5.
15. Urea forms a yellow-coloured complex with p-dimethylaminobenzaldehyde (DMAB) reagent in low acidic alcoholic solution at room temperature (25 ± 3 °C).
16. Urea analysis in milk the intensity of yellow colour measured at 440 nm.
17. In Urea analysis Pure milk Shows light yellow colour.
18. Nessler’s test is used to detect the ammonium salt in milk.
19. Ammonium salts is added to raise the Solid Not Fat (SNF) in milk.
20. Nessler’s reagent is an alkaline solution of potassium mercuric iodide (K₂HgI₄).
21. Nessler’s reagent reacts with Iodine to give Yellowish brown colour.
22. If Ammonium sulphate is added in milk it is also detect by Kjeldhal method.
23. Barium chloride reacts with sulphate in milk to give turbidity.
24. Barfoed’s test is used to identify the presence of monosaccharides and can identify reducing monosaccharides when disaccharides are present.
25. Barfoed’s test is used to detect the glucose in milk.
26. Barfoed’s reagent is copper acetate.
27. Monosaccharides (glucose) can reduce copper fast compare than disaccharides.
28. Added sodium chloride (salt) in milk is detected by silver nitrate and potassium chromate reagent.
29. Sodium chloride reacts with AgNO₃ and Pot.chromate to form yellow colour.
30. Chocolate brown precipitates indicate the absence of added NaCl in Milk.
31. Diphenylamine test is used to detect the nitrates in milk.
32. Nitrates are food preservatives.
33. Nitrates react with diphenylamine in sulphuric acid to give blue colour.
34. The end point of Nitrate test is Formation of blue ring at the junction of two solutions indicates adulteration of milk with nitrate or surface water
35. Colour development is used to detect the Neutralizers in milk.
36. Neutralization of milk increase in the pH of the milk.
37. Phenol red indicator is used for Neutralizer identify in milk.
38. Phenol red shows colour transition from yellow to red over the pH range 6.8 to 8.2.
39. Phenol red turns bright pink at pH above 8.2.
40. The milk adulterated with neutralizer reacts with Phenol red it shows pinkish orange colour.
41. Pure milk reacts with phenol red to form yellow colour.
42. Chlorate present in the hypochlorite reduced by stannous chloride to form yellowish fluorescence colour.
43. Hypochlorite is used as a sanitizer in dairy forms.
44. Quaternary Ammonium compounds may be present in milk due to some residual detergent solution remaining after bottle washing
45. Quaternary Ammonium compounds determined by titration with a standard anionic detergent solution.
46. Quaternary Ammonium compounds react with eosin indicator to form red or pink colour.
47. Anionic detergents may used as a “synthetic milk” formulation.
48. Detergents may be intentionally added in milk to emulsify the added vegetable oil in milk.
49. Methylene blue is cationic dye which forms complex with anionic detergents.
50. Blue colour develops in chloroform layer it is Anionic detergents.
51. Blue colour in milk layer it is non –adultered.
52. Hehner test is used to detect the Formaldehyde in milk.
53. Hehner test – An aldehyde – Oxidation reaction of aromatic amines.
54. Hehner test – Concentrated sulphuric acid and ferric chlorides is used
55. In hehner test ferric chloride acts as a oxidizing agent.
56. The end point of hehner test is violet colour.
57. The formaldehyde reaction depends on the presence of the tryptophan in the protein molecule. The violet colour develops as a result of the reaction of oxidized formaldehyde with tryptophan. The intensity of the reaction with different proteins varies in direct proportion to the amount of tryptophan present in the protein molecule
58. Leech test is used to detect the formaldehyde in milk.
59. Leech test – Concentrated Hydrochloric acid and ferric chlorides is used
60. Hydrogen peroxide (H₂O₂) is used as a preservative for milk.
61. Hydrogen peroxide in milk sample reacts with vanadium pentoxide to give pink or red colour.
62.  Hydrogen peroxide in milk sample reacts with phenylenediamine to give blue colour.
63. Hydrogen peroxide present in milk sample liberates iodine from potassium iodide which in presence of starch gives blue colour.
64. Milk sample treated with Hydrochloric acid and tip in turmeric paper it shows red colour indicates presence of borax / boric acid.
65. Boric acid is used as a preservative in milk.
66. Boric acid prevents milk going to sour.
67.  Salicylic acid used as a preservative in milk.
68. Salicylic acid is added to increase shelf life of the Milk.
69. Salicylic acid reacts with ferric chloride to give violet colour.
70. Maltodextrin is added in milk to increase the SNF ratio for milk
71. Maltodextrin is a carbohydrate but not sugar.
72. The dextrins having chain length of 8 DP (degree of polymerization) to 15 DP forms complex with iodine giving yellow-brown to brown to reddish purple colour as chain length increases. while, the chain length more than 45 DP gives blue colour.
73. The efficiency of pasteurization assessed by alkaline phosphatase in milk.
74. Alkaline phosphatase test disodium para-nitrophenyl phosphate which is used as a substrate for alkaline phosphatase, liberates a yellow-coloured compound para-nitrophenol, under the alkaline conditions in the presence of alkaline phosphatase.
75. In alkaline phosphatase test , p-Nitrophenol when present in the acidic medium remains in an undissociated colorless form, while it readily gets converted into its quinoid structure under alkaline conditions to form a yellow-coloured product.
76. Pasteurized milk giving readings less than 10 μg of p-nitrophenol shall be recorded as negative for alkaline phosphatase.
77. Efficiency of sterilization in milk check by turbidity test.
78. The turbidity test is not suitable for UHT Milk.
79. The turbidity test depends upon the denaturation of proteins of milk, especially albumin after sterilization. When solutions of inorganic salts or acids are added, albumin separates with the casein.
80. The Milk sample after treatment with ammonium sulphate is filtered, and heating of the filtrate shows turbidity due to the presence of albumin on account of insufficient heat treatment. If milk has been sterilized properly, all albumin will have been precipitated and no turbidity will be produced
81. Fat content in liquid milk sample can be estimated either by Gerber method (volumetric method) or Rose-Gottlieb method (gravimeteric method).
82. Protein / Nitrogen content in milk samples can be estimated by Kjeldhal method.
83. In kjeldhal method Copper sulphate acts as a catalyst.
84. In kjeldhal method nitrogen is convert to ammonium sulphate, the liberated ammonia trapped using Boric acid.

Fat:

The Gerber method is suitable as a routine or screening test. It is an empirical method and reproducible results can be obtained if procedure is followed correctly. The cream sample is mixed with sulphuric acid and iso-amyl alcohol in a special Gerber tube, permitting dissolution of the protein and release of fat. The tube is centrifuged and the fat rising into the calibrated part of the tube is measured as a percentage of the fat content of the cream sample. This method can be used for routine purposes.

Rose-Gottlieb Method is a gravimetric method in which fat globule membrane of milk fat globules is ruptured by addition of ammonia to cream sample to liberate the fat. The liberated fat is extracted using combination of solvents viz., diethyl ether and petroleum ether. The solvents are evaporated and obtained fat is dried and weighed. This method is considered suitable for reference purposes. Strict adherence to details is essential in order to obtain reliable results.

Protein:

In the first step, the protein is digested using concentrated sulphuric acid in presence of a catalyst (potassium sulphate/copper sulphate). In this step, all the organic material is oxidized except nitrogen, which is converted to ammonium sulphate. In the second step, the digest is neutralized with alkali to liberate ammonia . The ammonia distilled is collected in boric acid. In the third step, the collected ammonia in boric acid is titrated with standard hydrochloric acid in the presence of a methyl red-bromocresol green indicator until the green distillate changes from colourless to pink (methyl red, methylene blue indicator can also be used).

The quantity of acid required for titration is equivalent to the concentration of ammonia in the distillate and to the nitrogen content of the original protein containing sample.

The total amount of protein is calculated using the conversion factor of 6.38.

Ammonium sulphate (contains 21 % nitrogen) used as a standard for recovery test.