MCQ Detailed View

The fermentation of starch into alcohol is a multi-step biochemical process that involves several enzymes acting in a specific sequence. The correct order is Diastase → Maltase → Zymase.

1. 
   

   Action of Diastase
   Starch is a complex carbohydrate made of glucose units. On its own, yeast cannot directly ferment starch. The enzyme diastase (a type of amylase) first breaks down starch into smaller disaccharides, mainly maltose. This step is crucial because it makes the starch soluble and easier to convert further.

   
   


2. 
   

   Action of Maltase
   The disaccharide maltose formed in the first step is then acted upon by the enzyme maltase, which hydrolyzes maltose into two molecules of glucose. Glucose is the basic sugar that can undergo fermentation by yeast enzymes.

   
   


3. 
   

   Action of Zymase
   Finally, the enzyme complex zymase, secreted by yeast cells, ferments glucose into ethanol (C₂H₅OH) and carbon dioxide (CO₂). This is the classic alcoholic fermentation process:

   
   

C₆H₁₂O₆ → 2 C₂H₅OH + 2 CO₂

Thus, the complete sequence is:

• 
  

  Starch → (diastase) → Maltose

  
  


• 
  

  Maltose → (maltase) → Glucose

  
  


• 
  

  Glucose → (zymase) → Ethanol + CO₂

  
  

Importance of the process:
This sequence is industrially significant because it forms the basis of producing alcoholic beverages, industrial ethanol, and biofuels. It also illustrates the interconnection of enzymatic catalysis and organic chemistry reactions.

Option analysis:

• 
  

  Diastase → Zymase → Maltase is wrong because zymase cannot act before glucose is formed.

  
  


• 
  

  Zymase → Maltase → Diastase is incorrect as the order is reversed.

  
  


• 
  

  Maltase → Diastase → Zymase is also incorrect since starch must first be broken down by diastase.

  
  


• 
  

  Diastase → Maltase → Zymase is correct and matches the natural biochemical pathway.

  
  

Therefore, the correct enzyme sequence in starch fermentation is Diastase → Maltase → Zymase.