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What is the specific gravity of milk?
The ratio between the weight of a given volume of milk to the same volume of standard substance (water).
What is the standard specific gravity range for cow's milk?
What factors affect the specific gravity of milk?
The removal of fat from milk increases its specific gravity.
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Milk serum is prepared by removing __________ from milk.
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What is the purpose of using a lactometer in milk analysis?
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What are the two types of milk serum mentioned?
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What is the significance of specific gravity in milk analysis?
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Study Notes
Milk Hygiene Overview
- Conducted under supervision of Prof. Dr. Nagah Mohamed Saad and Prof. Dr. Enas El-Prince Mohammad.
- Practical focus on physical examination of milk.
Specific Gravity of Milk
- Defined as the ratio of the weight of a given volume of milk to an equal volume of standard substance (water).
- Standard weight of 1 mL of water at 4°C is 1 g.
- Calculation method: Specific gravity (sp.gr.) = W (weight of milk in kg) / V (volume in liters).
Factors Affecting Specific Gravity
- Total solids content directly influences sp.gr.
- Temperature impacts density and subsequently sp.gr.
- Fat percentage matters as fat has a lower sp.gr. (0.92) than water (1).
Measurement Procedure
- Use a lactometer for determining sp.gr. of milk.
- Milk should rest for 2 hours post-milking to eliminate gas bubbles.
- Fill 250 mL of milk in a graduated cylinder.
- Ensure that the lactometer floats upright in the milk without touching the bottom.
- Record two readings: lactometer value and temperature in °C.
Calculation Method for Specific Gravity
- Use Correct Lactometer Reading (C.L.R.) formula:
- Specific gravity = 1.0 + C.L.R. (L.R.± ((°F – 60) x 0.1)).
- Temperature conversion: °F = (°C x 9/5) + 32.
- Compare sp.gr. of milk to known standards from normal animals.
Normal Values for Specific Gravity
- Cow’s milk: typical range is 1.028 to 1.034; average is 1.032.
- Buffalo's milk: typical range is 1.033 to 1.036; average is 1.034.
Significance of Specific Gravity
- Indicates possible adulteration, such as the addition of water (H2O).
- Reflects the effect of partial skimming on milk composition.
- Addition of skim milk can lower sp.gr. but decrease fat percentage while increasing solids-not-fat (SNF) content.
Specific Gravity of Milk Serum
- Distinction between milk plasma (skim milk) and milk serum (whey).
- Milk serum is created by removing fat and casein from milk.
Preparation Methods for Milk Serum
-
CuSO4 Milk Serum:
- Involves adding copper sulfate solution (71.5 g/liter) to precipitate fat and protein.
-
Acetic Acid Milk Serum:
- Involves adding 25% acetic acid to precipitate fat and casein.
- Both methods require specific ratios and filtration processes.
Comparison Between Serum Types
-
CuSO4 Milk Serum:
- Action: Precipitates fat and protein.
- Turbidity: Clear with no protein presence; blue color.
- Refractive index: Measure indicates purity.
-
Acetic Acid Milk Serum:
- Action: Precipitates fat and casein.
- Turbidity: Turbid due to whey protein presence; colorless.
Practical Applications
- Understanding specific gravity and milk serum characteristics is crucial for assessing milk quality and safety.
- Methods outlined can be used for quality control in dairy processing and food hygiene evaluations.
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Description
This quiz covers the fundamental concepts of milk hygiene and the measurement of specific gravity. Students will learn about factors affecting specific gravity and the proper procedures for measurement. The focus is on understanding the physical properties of milk and their practical applications.
