Final answer:
The pH decreases in milk after adding pancreatin because the proteolytic enzymes in pancreatin break down milk proteins, releasing hydrogen ions and lowering the pH. Enzymatic activity and the precipitation of casein at its isoelectric pH also contribute to this change.
Step-by-step explanation:
When pancreatin, a mixture of digestive enzymes produced by the pancreas, is added to different types of milk, pH-sensitive digestive enzymes begin to break down proteins such as casein found in milk. This process releases amino acids and peptides, leading to the generation of hydrogen ions which in turn lowers the pH. Since the pH decreases as the hydrogen ion concentration increases, the addition of pancreatin causes the pH of the milk to decrease.
Pancreatin contains proteolytic enzymes that aid in the digestion of proteins through a sequence from protein to metaprotein, proteone, peptone, and finally to peptides. As these enzymes cleave peptide bonds in the milk proteins, they ultimately increase the concentration of free hydrogen ions, contributing to the decreased pH. Remember, proteins like casein have an isoelectric pH, where they are less soluble and tend to precipitate out, which can contribute to further pH changes in milk.
Furthermore, enzymes in pancreatin are usually activated in the alkaline conditions created by bicarbonate secreted by the pancreas into the small intestine. But when added to milk, their activity can still lead to protein breakdown and pH decrease, provided that the pH of the milk is not too low to inhibit their function.