A fermented vegetable product is safe primarily because it combines:[Fill in the blank]

Question

BlackTom AI · Accepted Answer

Lactic acid fermentation lowers pH and creates anaerobic, microbially competitive conditions, so...

1) Relevant knowledge points and concepts
- Lactic acid bacteria (LAB) on vegetables convert sugars to lactic acid, dropping product pH (often to ~3.5–4.0).
- Low pH inhibits many spoilage organisms and pathogens (Clostridium botulinum growth is prevented below ~4.6).
- Traditional vegetable fermentation is done in brine with limited oxygen (anaerobic or reduced-O2 environment).
- Microbial competition (dominance of LAB, production of bacteriocins) prevents colonization by undesirable microbes.
- Salt aids by selecting for LAB and reducing some spoilage organisms, but it does not by itself kill all pathogens.

2) Complete reasoning, step by step
- Vegetables naturally carry LAB. Adding salt and creating brine extracts sugars and suppresses many non-LAB microbes.
- Packing under brine reduces oxygen exposure, favoring facultative/obligate anaerobes like LAB and hindering aerobic spoilage organisms.
- LAB ferment sugars to lactic acid; acid accumulates, and pH drops quickly.
- The low-pH environment plus competitive exclusion (LAB occupy resources and produce antimicrobial compounds) prevents the growth of pathogens and spoilage organisms, making the product safe.

3) Calculations/intermediate steps
- Typical safe threshold: pH < 4.6 prevents C. botulinum toxin formation; fermented vegetables commonly reach pH ~3.5–4.0, well below that threshold.

4) Why the correct answer is correct
- Option C lists the three main protective factors: low pH (acid), reduced oxygen (anaerobic conditions), and microbial competition (LAB dominance). These three together explain why fermented vegetables are microbiologically stable and safe.

5) Why other options are incorrect
- A: High salt helps but does not “kill all spoilage and pathogenic organisms”; salt levels used are selective, not sterilizing.
- B: High temperature and oxygen exposure favor spoilage and pathogens, not safety.
- D: High nutrient availability and neutral pH would promote microbial growth, increasing risk rather than ensuring safety.

6) Conclusion
These points confirm that the safe combination is low pH, reduced oxygen, and microbial competition, matching the provided answer C.

A fermented vegetable product is safe primarily because it combines:[Fill in the blank]单项选择题

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