Food and dairy microbiology — heterofermentative lactic acid bacteria: Which microorganism listed is classically heterofermentative, producing lactic acid along with CO2 and ethanol/acetate from sugars?

Introduction / Context:
Lactic acid bacteria (LAB) are grouped as homofermentative or heterofermentative based on their glycolytic pathways and end products. This classification affects flavor, gas production, and texture in fermented foods.

Given Data / Assumptions:

• We must identify a heterofermentative organism.
• Heterofermenters generate lactic acid plus CO2 and ethanol/acetate via the phosphoketolase pathway.
• Homofermenters produce primarily lactic acid via the Embden–Meyerhof pathway.

Concept / Approach:
Leuconostoc mesenteroides is a textbook heterofermentative LAB, contributing to flavor and gas in sauerkraut and some dairy fermentations. In contrast, L. delbrueckii and L. bulgaricus are typically homofermentative, yielding mostly lactic acid and little gas.

Step-by-Step Solution:
List candidates and recall metabolic type from food micro references.Match heterofermentation to Leuconostoc mesenteroides.Exclude typical homofermenters used in yogurt (e.g., L. delbrueckii, L. bulgaricus).

Verification / Alternative check:
CO2 bubble formation and flavor notes in vegetable ferments align with Leuconostoc activity.

Why Other Options Are Wrong:

• L. delbrueckii/L. bulgaricus: Homofermentative.
• Lactobacillus pentose: Likely refers to L. pentosus, often facultative heterofermentative, but the classical single best answer remains Leuconostoc mesenteroides.
• Streptococcus thermophilus: Primarily homofermentative.

Common Pitfalls:
Assuming all LAB behave similarly across substrates; pathway choice matters to product profiles.

Final Answer:
Leuconostoc mesenteroides.