112. Hygiene evaluation of milk. Taking of the milk samples. Laboratory tests.

Why is milk considered an excellent food?

Milk is a complete food because it contains a balanced mixture of essential nutrients:

• Proteins: High-quality with all essential amino acids.

• Fats: Includes saturated fatty acids needed for energy and cell membranes.

• Sugars: Mainly lactose, providing energy.

• Vitamins: All except vitamin C.

• Minerals: Especially calcium, important for bones and teeth.

What carbohydrate is present in milk?

Milk contains lactose,

• a disaccharide sugar, also known as milk sugar.

what is the main milk protein in milk

casein

How is casein formed in milk?

Casein, the main milk protein, forms by combining with calcium ions, which help stabilize the protein structure.

What tool is used to measure milk density?

The lactometer is used to measure the density or specific gravity of milk.

How does fat content affect milk density?

• Fat is less dense than water;

• removal of fat increases the density of milk.

How is milk density measured with a lactometer?

• Pour 200 ml milk into a cylinder.

• Gently insert the lactometer until it reaches the 30 scale.

• Wait 1 minute at 20°C, then read the scale.

• Adjust reading by 0.2 per °C if temperature deviates.

How is milk acidity determined?

• Acidity is measured by titrating milk with 0.1 N NaOH

• using phenolphthalein as an indicator.

• The result is expressed in degrees of Toerner.

What is the normal acidity range of milk in degrees of Toerner?

between 15 to 21 degrees Toerner.

what is the degree of Toerner

a unit used to express the titratable acidity of milk

• basically, how much acid is present in a given volume of milk.

What does the degree of Toerner represent?

1° Toerner = the amount of acid in 100 ml of milk that can be neutralized by 1 ml of 0.1 N NaOH (sodium hydroxide solution).

e.g If it takes 17 ml of 0.1 N NaOH to neutralize 100 ml of milk, the milk has an acidity of 17° Toerner.

What is pasteurization?

Pasteurization is a heat treatment designed to destroy pathogenic bacteria in milk while causing minimal changes to taste and nutrients.

Does pasteurization kill all bacteria?

No, it kills about 90% of bacteria, but thermoduric bacteria and bacterial spores may survive.

What are the main pasteurization methods?

• Holder method: 63–66°C for 30 minutes

• HTST (High Temperature Short Time): 72°C for 15 seconds

• UHT (Ultra High Temperature): 125°C for a few seconds

What is a downside of UHT pasteurization?

UHT can destroy vitamins, lowering milk's nutritional quality.

How long does pasteurized milk maintain quality at 18°C?

It remains fresh for 8 to 12 hours at 18°C.

What test confirms if milk is pasteurized?

The peroxidase test:

• pasteurized milk should be negative (no peroxidase activity).

What is the principle of the peroxidase test?

• Peroxidase enzyme breaks down hydrogen peroxide (H₂O₂),

• releasing iodine which reacts with starch to form a blue color.

• Blue color means enzyme is present

• therfore milk is not properly pasteurized.

How is the peroxidase test performed?

Add iodine-starch solution and H₂O₂ to milk;

• shake and observe color change.

What does the presence of sodium bicarbonate in milk indicate?

• Sodium bicarbonate is an adulterant,

• added to prolong shelf life

• but it destroys vitamins and compromises quality.

How to test for sodium bicarbonate in milk?

Add alcohol and rosolic acid to milk;

• a raspberry-red color indicates presence.

How is microbial content of milk assessed?

• Standard colony count (total bacteria load)

• Specific tests for pathogens such as Staphylococcus aureus, E. coli, Salmonella.