In industrial microbiology, Candida utilis (also known as Torula yeast) is used to ferment spent sulphite (sulfite) waste liquor from the pulp and paper industry. This feedstock contains a mixture of wood-derived sugars. Which sugars can C. utilis efficiently ferment in this process?

Introduction / Context:
Spent sulphite liquor is a by-product of wood pulping that contains a complex mixture of soluble sugars released from hemicellulose and cellulose. Selecting a microorganism that can utilize multiple sugar types is essential for efficient fermentation and waste valorization. Candida utilis is widely applied because it can metabolize a broad spectrum of sugars, enabling high conversion yields and single-cell protein production.

Given Data / Assumptions:

• Feedstock: spent sulphite liquor rich in glucose, mannose, xylose, and other wood sugars.
• Organism: Candida utilis (Torula yeast) adapted to lignocellulosic hydrolysates.
• Goal: maximize sugar utilization and fermentation efficiency.

Concept / Approach:
The key requirement is pentose- and hexose-fermenting capacity. Many conventional yeasts (e.g., Saccharomyces cerevisiae) readily ferment hexoses but poorly ferment pentoses without engineering. C. utilis, however, can assimilate both sugar classes, making it suitable for mixed-sugar hydrolysates typical of lignocellulosic streams.

Step-by-Step Solution:

Verification / Alternative check:
Industrial practice and literature on single-cell protein production from pulp mill liquors consistently cite C. utilis because of its pentose assimilation, confirming the choice.

Why Other Options Are Wrong:

• Hexoses only: ignores pentose-rich hemicellulose sugars.
• Pentoses only: C. utilis also ferments hexoses efficiently.
• None/Disaccharides only: contradicts established metabolic breadth.

Common Pitfalls:
Assuming all yeasts behave like S. cerevisiae; failing to consider the pentose fraction of lignocellulosic hydrolysates.

Final Answer:
Both hexoses and pentoses