Which enzyme initiates carbohydrate digestion in the mouth, and what is its substrate?

• A. Lingual lipase; triglycerides
• B. Salivary amylase; starch
• C. Sucrase; sucrose
• D. Pepsin; protein

Answer: (B)

Carbohydrate digestion starts in the mouth, with salivary amylase breaking down starch. This enzyme is secreted by the salivary glands and in the mouth it cleaves the α-1,4 glycosidic bonds in starch, producing maltose and dextrins. The substrate here is starch, which is the big carbohydrate in many diets. This early step occurs in the mouth because saliva provides the enzyme in a near-neutral environment; once swallowed, the acidic stomach inactivates amylase, so later digestion continues in the small intestine with pancreatic amylase and other enzymes.

Lingual lipase acts on fats, not carbohydrates, so it’s not initiating carbohydrate digestion. Sucrase works on sucrose, but in the small intestine rather than in the mouth. Pepsin digests proteins in the stomach, not carbohydrates.