In food science and human nutrition, what is the main protein found in milk that forms the bulk of the curd during coagulation?

Introduction / Context:
Milk is an important source of dietary protein, especially for children. Several different proteins are present in milk, but one group forms the major fraction and is responsible for the formation of curd when milk is coagulated. This question asks you to identify the principal milk protein that predominates in most mammalian milk.

Given Data / Assumptions:

• We are considering normal cow or buffalo milk composition as an example.
• The options include albumin, globulin, globin, casein, and collagen.
• Curd formation involves coagulation of specific milk proteins under the action of acids or enzymes.
• We assume basic knowledge of nutritional chemistry.

Concept / Approach:
Milk proteins are broadly divided into casein and whey proteins. Casein proteins make up the majority and are present as micelles in milk. When milk is acidified or treated with rennet, casein precipitates to form curd, while most whey proteins remain in the liquid. Albumin and globulin are also present but in smaller amounts and are soluble. Globin is a component of hemoglobin, and collagen is a structural protein in connective tissues, not major milk proteins.

Step-by-Step Solution:
Step 1: Recall that casein constitutes the largest fraction of milk protein, often around eighty percent in cow milk. Step 2: Remember that curd formation during cheese making or yogurt preparation mainly involves coagulation of casein. Step 3: Note that albumin and globulin are whey proteins and remain mostly in the liquid portion when casein precipitates. Step 4: Recognize that globin is associated with hemoglobin in blood, not with milk composition. Step 5: Collagen is found in connective tissues such as skin, tendons, and cartilage and is not the main protein of milk. Step 6: Therefore, the main protein in milk is casein.

Verification / Alternative check:
Food science texts and dairy technology references consistently state that casein micelles are the dominant protein structures in milk and that they are responsible for cheese yield and curd characteristics. Nutritional labels and scientific analyses also separate protein into casein and whey components, with casein as the larger share. This confirms that casein is the primary milk protein.

Why Other Options Are Wrong:
Albumin and globulin are present but do not form the bulk of milk protein and are usually referred to as whey proteins. Globin is part of hemoglobin and is not a milk protein at all. Collagen is a structural protein of connective tissue and has a completely different distribution and function. None of these match the description of main milk protein that forms curd during coagulation.

Common Pitfalls:
Students sometimes confuse general blood plasma proteins like albumin and globulin with milk proteins because the names are familiar. Others may choose collagen simply because it is commonly mentioned as a protein, forgetting that it is associated with skin and bones rather than milk. When you see a question about principal milk protein and curd formation, casein should come to mind immediately.

Final Answer:
The main protein found in milk is Casein.