**Core Concept**
Whey proteins are a type of protein found in milk, comprising approximately 20% of the total protein content. They are classified into different types based on their molecular weight and composition.

**Why the Correct Answer is Right**
β-Lactoglobulin is the predominant whey protein in cow milk, accounting for approximately 50-60% of the total whey protein content. This is due to its stability and resistance to heat, making it a major component of whey protein isolates. β-Lactoglobulin is a globular protein that is rich in sulfur-containing amino acids, which contribute to its nutritional value.

**Why Each Wrong Option is Incorrect**
**Option A:** α-Lactalbumin is another type of whey protein in cow milk, but it is not the predominant type. α-Lactalbumin is involved in the biosynthesis of lactose and is a major component of whey protein hydrolysates.
**Option B:** Glycomacropeptide is a component of whey protein, but it is not a type of whey protein. Glycomacropeptide is a peptide that is derived from the digestion of κ-casein.
**Option C:** Serum albumin is a type of protein found in blood plasma, not in milk. While serum albumin is a major protein in blood, it is not a type of whey protein.

**Clinical Pearl / High-Yield Fact**
Milk proteins, including whey proteins, are an important source of essential amino acids for human nutrition.

**Correct Answer:** C. β-Lactoglobulin.