If casein is proteolyzed, what visual change occurs in litmus milk?

When casein is proteolyzed in litmus milk, the primary visual change observed is that the solution becomes clear. This occurs due to the breakdown of the casein protein into smaller peptides and free amino acids. The casein, which is typically responsible for the opaque, white color of litmus milk, is hydrolyzed, leading to the release of these smaller protein fragments. As a result, the milk loses its cloudiness and appears more transparent or clear.

This process can also alter the pH of the solution and may lead to changing colors in the indicator (litmus), but the most distinctive and immediate visual change is the clearing of the milk. This characteristic is often used in microbiology to assess the proteolytic activity of certain bacteria.