Question

Fermentation of starch solution to ethyl alcohol does not require:

• A. invertase
• B. diastase
• C. zymase
• D. maltase

Answer 1

Answer: (A)

invertase

Only sucrose requires invertase not the starch for the fermentation process for alcohol formation.

Sucrose is a dimer of glucose and fructose molecules. In the first step of alcoholic fermentation, the enzyme invertase cleaves the glycosidic linkage between the glucose and fructose molecules. Starch is hydrolysed to maltase by an enzyme known as diastase.

$C_{12}{H}_{22}{O}_{11}+H_{2}O+Invertase⟶2\left(C_6{H}_{12}{O}_6\right)$

$2\left(C_6{H}_{10}{O}_5\right)+n{H}_{2}O⟶n\left(C_{12}{H}_{22}{O}_{11}\right)$

$C_{12}{H}_{22}{O}_{11}+H_{2}O⟶2C_6{H}_{12}{O}_6$

$C_6{H}_{12}{O}_6⟶C_2{H}_{5}OH+2C{O}_2$

Finally yeast is added to maltase.

Yeast secrets two enzymes:

1. Maltase: converts maltose into glucose.

2. Zymase: converts glucose into ethanol

Yeast like most organisms can break down monosaccharides (glucose fructose) and disaccharides (sucrose aka table sugar and maltose) because they are water soluble. Starches cannot be absorbed for nutrients because the "sugars" they contain are linked together and cannot be dissolved due to their increased size. Once the starch is broken down it can be dissolved in the extracellular space and transported into the cell for fuel.