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Questions and Answers
What is the primary carbohydrate in milk that is hydrolyzed by microorganisms during the souring process?
Which of the following proteins is denatured and coagulated by heat in milk?
Which test is NOT used for the characterization of casein in milk?
What is produced when galactose is converted by lactobacilli during the souring of milk?
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What property do lactoglobulins carry that is crucial for young mammals?
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What is the main protein found in milk?
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Which component gives milk its nutritional complete profile?
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Which of the following vitamins is NOT found in significant amounts in milk?
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At what pH does casein precipitate in milk?
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Which of the following is true regarding the solubility of casein?
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How does the structure of globular proteins differ from fibrous proteins?
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What is unique about the composition of human milk compared to cow and goat milk?
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Which minerals are primarily found in milk?
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Study Notes
Milk Composition
- A highly nutritious food source.
- Contains vitamins (thiamine, riboflavin, pantothenic acid, Vitamin A, B12, and D), minerals (calcium, potassium, sodium, phosphorus, and trace metals), carbohydrates (primarily lactose), and lipids (fats).
- Cow's and goat's milk are nearly identical; human milk has less protein and minerals but more sugar. Human milk lacks iron and Vitamin C.
Globular Proteins in Milk
- Casein, lactalbumin, and lactoglobulin are globular proteins.
- Globular proteins are compact, nearly spherical, and readily form colloidal suspensions in water.
- Milk proteins are "complete proteins," containing all essential amino acids.
Casein
- The primary protein in milk.
- A phosphoprotein with phosphate groups attached to amino acid side chains.
- Three similar types exist (α-casein, β-casein, κ-casein), differing in molecular weight and phosphorus content.
- α-casein and β-casein are water-insoluble; κ-casein solubilizes them by forming micelles.
- Exists in milk as calcium caseinate.
- Has an isoelectric point of pH 4.6; insoluble below this pH.
- Milk's pH (around 6.6) keeps casein negatively charged and soluble. When pH decreases (e.g., milk souring due to lactic acid production), casein precipitates.
Other Milk Proteins
- Lactalbumin: The second most abundant protein; water-soluble; denatures with heat.
- Lactoglobulins: Present in smaller amounts than lactalbumin; denature and precipitate under similar conditions as lactalbumin; carry immunological properties.
Experiment Outline
- Extraction of Casein: Procedure for isolating casein detailed elsewhere.
- Characterization of Casein: Using Biuret, Ninhydrin, Xanthoproteic, Adamkiewicz, Molisch's, and Phosphate tests.
- Testing for Other Milk Nutrients: Procedures for identifying lactose, calcium, chlorides, and sulfates are detailed elsewhere.
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Description
Test your knowledge on the composition of milk and its globular proteins. This quiz covers various aspects of milk nutrition, including vitamins, minerals, and the structure of casein proteins. Explore milk's role as a complete protein source and understand the differences between types of milk.
