Which of the following enzyme converts starch into maltose?

The question asks which enzyme converts starch into maltose. Let's understand the functions of each enzyme step by step.

Starch is a polysaccharide, which is a complex carbohydrate made up of many glucose units. Maltose is a disaccharide composed of two glucose molecules. We need to find the enzyme that specifically breaks down starch into maltose.

Now, let's examine each option:

Option A: Diastase. Diastase is an enzyme that catalyzes the hydrolysis of starch into maltose. It is commonly found in germinating seeds and in saliva (as salivary amylase). The reaction can be represented as: $$\text{Starch} \rightarrow \text{Maltose}$$

Option B: Maltase. Maltase acts on maltose and breaks it down into two glucose molecules. It does not act on starch. The reaction is: $$\text{Maltose} \rightarrow 2\text{ Glucose}$$

Option C: Zymase. Zymase is an enzyme complex in yeast that converts simple sugars like glucose into ethanol and carbon dioxide during fermentation. It does not act on starch. The reaction is: $$\text{Glucose} \rightarrow \text{Ethanol} + \text{Carbon dioxide}$$

Option D: Invertase. Invertase hydrolyzes sucrose (a disaccharide) into glucose and fructose. It does not act on starch. The reaction is: $$\text{Sucrose} \rightarrow \text{Glucose} + \text{Fructose}$$

From this analysis, only diastase converts starch into maltose. Therefore, the correct enzyme is diastase.

Hence, the correct answer is Option A.