MICROBIOLOGY Study Guide - 2012

CHAPTER 9. PHYSIOLOGY OF MICROORGANISMS

9.5. FERMENTATION

9.5.3. Heterolactic Fermentation

Heterofermentative lactic acid Bacteria ferment CARBOHYDRATES via the oxidative Pentose Phosphate Pathway, producing a variety of end products, including lactic acid, carbon dioxide, ethanol, and/or acetic acid (Fig. 29). Specifically, Leuconostoc mesenteroides breaks down glucose According to the following equation:

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Fig. 29. Pathway of heterolactic Fermentation.

Enzymes involved in the fermentation: Ф₁ — hexokinase; Ф₆ — phosphoketolase; Ф₂ — glucose-6-phosphate dehydrogenase; Ф₇ — acetate kinase; Ф₃ — lactonase; Ф₈ — acetaldehyde dehydrogenase; Ф₄ — phosphogluconate dehydrogenase; Ф₉ — Alcohol dehydrogenase; Ф₅ — phosphopentose epimerase

Other heterofermentative bacteria (L. brevis, L. fermentum, etc.) convert acetyl phosphate into acetic acid, and glyceraldehyde-3-phosphate via Pyruvate into lactate. Excess hydrogen is accepted by glucose to form mannitol:

Homo- and heterofermentative lactic acid bacteria are essential for biotechnological processes such as The production of fermented dairy drinks, cottage cheese, sour cream, cheese, cultured butter, and dry-cured sausages. They play a major role in the pickling of fruits and vegetables, as well as in ensiling. They are also widely used in the baking industry to produce liquid Yeasts and Sourdough starters for rye and wheat bread.