A milkman adds a very small amount of baking soda to fresh milk.
a)Why does the pH of the fresh milk change from 6 to slightly alkaline
b)Why does this milk take a long time to set as curd.
a) The addition of baking soda (sodium bicarbonate) to fresh milk increases its pH from 6 to slightly alkaline (above 7) because baking soda is basic in nature. It acts as a buffer and neutralizes the acidic components present in fresh milk, such as lactic acid. This shift in pH towards alkalinity helps to stabilize the milk and increases its shelf life.
b) The milk takes a longer time to set as curd because baking soda, being alkaline, affects the protein structure in milk. The proteins in milk, primarily casein, are responsible for curdling or coagulating to form curd. When the pH of milk is alkaline, it interferes with the structure of proteins and hampers the curdling process. As a result, it takes a longer time for the milk to set as curd compared to when the pH is in the optimal range for curdling, which is slightly acidic.
a) The addition of baking soda, which is a base, increases the pH of the fresh milk from 6 to slightly alkaline. Baking soda is a common household base and when added to an acidic substance like milk, it neutralizes the acidity to some extent. This increase in pH makes the milk less acidic and more alkaline.
b) The reason why this milk takes a long time to set as curd is because the increased alkalinity caused by the baking soda interferes with the natural curdling process. Curdling of milk is the result of protein molecules in the milk forming a network or mesh-like structure, which traps the fat and liquid to form curd.
When the pH of the milk is slightly alkaline, the proteins in the milk are less likely to aggregate and form this network. The natural curdling process slows down or may not happen at all. As a result, it takes a longer time for the milk to set as curd when baking soda is added.