Question

The molecular weight of lactose in comparison to that of lactic acid is

• A. Equal
• B. Two times higher
• C. Three times higher
• D. Four times higher

Hint:

Biochemically, homofermentative lactic acid bacteria split one 12-carbon lactose molecule into four 3-carbon lactic acid molecules:
\[ \text{C}_{12}\text{H}_{22}\text{O}_{11} + \text{H}_2\text{O} \rightarrow 4 \ \text{C}_3\text{H}_6\text{O}_3 \]
Thus, the molecular weight of lactose is nearly 4 times that of lactic acid.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
The conversion of lactose into lactic acid by lactic acid bacteria is the core biochemical pathway of dairy fermentations.
Key Formula or Approach:
Let us compare the molecular formulas and weights of both compounds:
- Lactose (\(\text{C}_{12}\text{H}_{22}\text{O}_{11}\)):
\[ \text{Molecular Weight} \approx 342.3\text{ g/mol} \]
- Lactic Acid (\(\text{C}_3\text{H}_6\text{O}_3\)):
\[ \text{Molecular Weight} \approx 90.08\text{ g/mol} \]

Step 2: Detailed Explanation:
Let us calculate the ratio of their molecular weights:
\[ \text{Ratio} = \frac{\text{MW of Lactose}}{\text{MW of Lactic Acid}} = \frac{342.3}{90.08} \approx 3.8 \]
This value is closest to four times higher (specifically, one molecule of the disaccharide lactose is fermented to yield four molecules of lactic acid in homofermentative pathways).

Step 3: Final Answer
The molecular weight of lactose is approximately four times higher than that of lactic acid.