Unit 3 | Principles of Food Science and Nutrition | 5th Semester

Principles of Food Science and Nutrition

Unit III

Unit - III Syllabus

Physico-chemical properties of milk. Factors affecting of quality and quantity of milk.

Notes by Agricorn.in

Physico-chemical properties of milk

Milk is a complex fluid with a wide range of physico-chemical properties that make it suitable for a variety of food products. Some of the important physico-chemical properties of milk are:

1. pH: The pH of milk is around 6.7, which is slightly acidic. The pH of milk is influenced by the presence of certain compounds, such as lactic acid, which are produced by bacteria during fermentation.

2. Density: The density of milk is around 1.03 g/cm3, which is slightly greater than that of water. The density of milk is influenced by the fat and protein content of the milk.

3. Viscosity: Milk has a relatively high viscosity compared to water, which is due to the presence of proteins and other dissolved solids in the milk. The viscosity of milk can be influenced by factors such as temperature and agitation.

   Temperature is an important factor that can affect the viscosity of milk. As the temperature of milk increases, the viscosity decreases due to a reduction in the interaction between the milk components. Shear rate, or the rate at which the milk is subjected to mechanical stress, can also affect viscosity. At low shear rates, the viscosity of milk is higher, while at high shear rates, the viscosity decreases.

4. Surface tension: Milk has a relatively high surface tension compared to water, which is due to the presence of surface-active compounds such as casein and whey proteins.

5. Freezing point: The freezing point of milk is around -0.54°C, which is slightly lower than that of water. The freezing point of milk is influenced by the concentration of dissolved solids in the milk.

6. Conductivity: Milk is a good conductor of electricity due to the presence of dissolved minerals and ions such as calcium, potassium, and chloride.

7. Heat stability: Milk has relatively low heat stability, which means that it can easily undergo denaturation and coagulation at high temperatures. The heat stability of milk can be influenced by factors such as pH, the presence of certain minerals, and the type of heat treatment used.

8. Foaming properties: Milk has good foaming properties due to the presence of surface-active compounds such as casein and whey proteins. This property is important in the production of whipped cream, ice cream, and other dairy products.

Overall, the physico-chemical properties of milk play a crucial role in determining its suitability for different food products and processing techniques.

Factors affecting of quality and quantity of milk

Several factors can affect the quality and quantity of milk produced by dairy animals. Some of the key factors are:

1. Breed: The breed of dairy animal can have a significant impact on the quality and quantity of milk produced. For example, Holstein cows are known for their high milk production, while Jersey cows produce milk with a higher butterfat content.
2. Nutrition: The diet of dairy animals is critical for milk production. A diet that is high in energy and protein can improve milk production, while a diet that is deficient in certain nutrients can lead to decreased milk production and poor milk quality.
3. Milking frequency: The frequency of milking can also impact milk production. Dairy animals that are milked more frequently tend to produce more milk overall.
4. Environmental conditions: Environmental factors such as temperature, humidity, and air quality can also affect milk production. Dairy animals that are exposed to extreme heat or cold may produce less milk, while animals that are housed in poorly ventilated areas may be more susceptible to udder infections.
5. Genetics: Genetic factors can also play a role in milk production. For example, some dairy animals may have a genetic predisposition to producing higher quality or higher quantity milk.
6. Health: The health of dairy animals is also critical for milk production. Animals that are sick or have udder infections may produce lower-quality milk or may need to be treated with antibiotics, which can affect the quality of the milk.
7. Milking technique: The milking technique used can also affect the quality of the milk. Improper milking techniques can result in contamination of the milk and decreased milk quality.
8. Seasonal variations: Milk production and quality can also vary seasonally. For example, milk production tends to decrease during the hot summer months, while milk fat content may increase during the winter months.
9. Age of the animal: The age of the dairy animal can also affect milk production. Generally, younger animals tend to produce less milk than older animals, but the quality of the milk may be higher in younger animals.
10. Milking hygiene: Proper milking hygiene is essential for maintaining milk quality. Any contamination during the milking process can result in lower milk quality. It is important to ensure that the milking equipment and environment are clean and free from any contaminants.
11. Milk handling and storage: Proper handling and storage of milk are also important for maintaining milk quality. Milk should be cooled and stored at the appropriate temperature to prevent bacterial growth and spoilage.
12. Lactation stage: Milk production is highest during the early stages of lactation, and then gradually declines. Proper management of the lactation cycle can help maximize milk yield.

Notes by Agricorn.in