Sulfite waste liquor fermentation: Candida utilis is employed because of its ability to ferment which class of sugars present in this substrate?

Introduction / Context:
Sulfite waste liquor is a by-product of paper pulp processing and contains significant amounts of hemicellulose-derived pentose sugars. Selecting microorganisms capable of utilizing pentoses is crucial for single-cell protein (SCP) production and value recovery from this waste stream.

Given Data / Assumptions:

• The organism is Candida utilis, a yeast used in SCP processes.
• The substrate contains pentoses such as xylose and arabinose.
• We focus on the primary sugar class enabling growth and fermentation.

Concept / Approach:
Candida utilis is well known for its ability to assimilate pentose sugars, a key reason it became a favored microbe for upgrading sulfite waste liquor into microbial biomass. While it can also use hexoses under many conditions, the distinctive capability for pentoses makes it suitable for this specific feedstock.

Step-by-Step Solution:

Verification / Alternative check:
Classic SCP literature and pulp-and-paper bioprocess case studies emphasize C. utilis on pentose-rich waste streams, corroborating this answer.

Why Other Options Are Wrong:

• Sucrose, glucose, and maltose may be utilizable by many yeasts but are not the defining advantage here.
• Lactose utilization is more characteristic of organisms like Kluyveromyces.

Common Pitfalls:
Assuming any fermentable sugar works equally; missing that the economic hook is valorizing pentose-rich residues.

Final Answer:
Pentose