What color change indicates alkaline production in Litmus Milk?

The color change from pink to blue in Litmus Milk indicates alkaline production because it reflects the pH shift caused by the metabolic activity of certain bacteria. In a Litmus Milk medium, when bacteria ferment lactose, acid is produced, leading to a reduction in pH and resulting in a pink color. However, certain bacteria possess the ability to utilize proteins and produce ammonia, which raises the pH and changes the color of the medium to blue. This change signifies that the bacteria are producing alkaline substances, demonstrating their metabolic activity and providing insight into their biochemical characteristics.

The other potential choices do not accurately represent the pH change associated with alkaline production in Litmus Milk. The transition from blue to purple does not indicate alkaline conditions; instead, blue typically represents basic conditions already. Green to yellow usually signifies acidic conditions due to acid production during fermentation, and the purple to brown transition is not a standard or recognized color change in the context of Litmus Milk and does not relate to the production of alkaline substances.