Cottage cheese is produced by acidifying milk, bringing the pH of the milk down to the isoelectric point of casein, the main milk protein that creates the cottage cheese curd. What is the net charge of the casein at its isoelectric point?

2
3
1
0

The correct answer is 0.

Explanation

Milk is basically a mixture of many kinds of proteins, which are further divided into 3 main categories:  

Casein being a protein is made from many amino acids. Depending on the pH of milk system, each amino acid has a negative and a positive charge. At some value of pH, the positive and negative charges on casein will be in balance, thus leaving Zero net charge at its isoelectric point.