Ethanol from whey lactose: which microorganism is commonly used to ferment lactose in whey to alcohol in industrial practice?

Introduction / Context:
Whey, a dairy by-product rich in lactose, represents a large renewable substrate for producing ethanol and other value-added products. Efficient fermentation hinges on microorganisms capable of metabolizing lactose directly, which many conventional brewing yeasts cannot do without prior hydrolysis.

Given Data / Assumptions:

• Lactose-fermenting yeasts such as Candida pseudotropicalis (syn. Kluyveromyces marxianus) are used for whey valorization.
• Saccharomyces cerevisiae does not natively ferment lactose; it needs lactose hydrolysis to glucose/galactose first.
• Industrial goals include high productivity, thermotolerance, and ability to handle whey components.

Concept / Approach:
Select a yeast that possesses beta-galactosidase activity or expresses permease systems enabling lactose utilization. Candida pseudotropicalis/Kluyveromyces marxianus meets these criteria and is historically reported for ethanol production from whey streams, often with favorable growth rates at elevated temperatures.

Step-by-Step Solution:

Verification / Alternative check:
Process descriptions and academic reports on whey ethanol consistently list Kluyveromyces marxianus/C. pseudotropicalis as prime candidates due to lactose metabolism and thermotolerance.

Why Other Options Are Wrong:

• Saccharomyces cerevisiae: Standard ethanol producer, but not directly on lactose.
• Candida utilis: Valued for single-cell protein; not the typical ethanol producer from lactose.
• None of these: Incorrect because a correct organism is listed.
• Kluyveromyces lactis: Lactose-utilizing, but traditionally more associated with dairy enzyme production than high-rate ethanol; the most cited ethanol strain here is C. pseudotropicalis/K. marxianus.

Common Pitfalls:
Assuming any ethanol yeast can ferment lactose; neglecting pretreatment (clarification, deproteinization) steps that improve fermentation performance.

Final Answer:
Candida pseudotropicalis