10 Questions
What type of bond forms when a carboxylic group of one amino acid combines with the amino group of another amino acid?
Peptide bond
What is the isoelectric point of casein?
pH 4.6
What is the primary reason milk fat globule membranes are important?
They protect the globules from lipase enzyme action
Which factor does NOT influence the size of fat globules in milk?
Temperature of the milk
What happens to amino acids in an alkaline medium?
They carry negative charges
Which of the following describes the amphoteric reaction of fresh milk?
It turns red litmus paper to blue and blue litmus paper to red
Which of the following is NOT a component that stabilizes milk-fat emulsion?
Cholesterol
Which type of amino acids interaction occurs in an acidic medium?
Positive charges are prevalent
What important role do phospholipids play in dairy products?
They stabilize foam and act as emulsifying agents
What major component forms proteins in milk?
Amino acids
Study Notes
Milk Proteins
- Milk proteins are amphoteric, reacting with both acids and bases due to having amino and carboxyl groups in their chemical structure.
Casein Proteins
- Casein is the main protein of milk, making up approximately 80% of total milk proteins.
- Casein coagulates or precipitates at pH 4.6, which is the principle behind cheese curd formation.
- The casein family consists of several types, including α-s1, α-s2, β, and κ, each with unique properties and functions.
- Casein is suspended in milk as a complex called a micelle, which can associate with calcium to form calcium phosphate salts.
- α-s Casein is sensitive to calcium ions, while κ-Casein is insensitive and stabilizes the casein micelle structure.
Whey Proteins
- Whey proteins make up around 20% of total milk proteins and do not contain phosphorus.
- Whey proteins remain in solution in milk at pH 4.6 and include proteins such as β-lactoglobulin, α-lactalbumin, blood serum albumin, immunoglobulins, and minor proteins.
- β-Lactoglobulin is thought to be a carrier of vitamin A, while α-lactalbumin plays a critical role in lactose synthesis.
Properties of Casein
- Casein is heat-stable, surviving pasteurization at temperatures around 62-71°C, unlike whey proteins, which are denatured at these temperatures.
- Casein solubility is pH-dependent.
Industrial Applications of Casein
- Casein is used in the plastics industry, in the manufacture of book covers and magazines, and in the textile and paint industries.
Milk Fat Globules
- The size of fat globules in milk depends on factors such as animal type, breed, and nutrition.
- Milk fat globules are surrounded by a thin membrane composed primarily of lipids and proteins, which protects them from lipase enzyme action.
Phospholipids
- Phospholipids play an essential role in nutrition, particularly in bone building and brain cell development.
- Phospholipids act as emulsifying agents and stabilize foam, making them crucial in the manufacture of products like ice cream.
Amino Acids and Proteins
- Amino acids combine chemically to form protein molecules with high molecular weight through peptide bonds.
- The peptide bond is formed by the combination of a carboxylic group of one amino acid with the amino group of another.
Amphoteric Reaction of Proteins
- Amino acids contain acidic and basic groups, allowing them to interact with acids and alkalis.
- In alkaline media, amino acids carry negative charges, while in acidic media, they carry positive charges.
This quiz covers the properties of milk proteins, including their amphoteric reaction and separation methods. Learn about casein and whey proteins and their composition in milk.
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