Chapter 3 Factors Affecting The Growth And Survival Of Micro-organisms In Foods

Question 0

Generally, what are the micro-organisms’ optimal pH range?

Answer 0

Bacteria 6.0-8.0
Yeasts 4.5-6.0
Filamentous fungi 3.5-4.0
(Lactobacilli and acetic acid bacteria 5.0-6.0)

Question 1

What are the factors affecting the development of microbial associations in food?

Answer 1

Intrinsic factors: nutrients, pH and buffering capacity, redox potential, water activity, antimicrobial constituents and structures
Environmental factors: relative humidity, temperature, gaseous atmosphere
Implicit factors: specific growth rate, mutualism, antagonism, commensalism
Processing factors: slicing, washing, packing, irradiation, pateurization

Question 2

Give examples of obligate anaerobes and aerotolerant anaerobes.

Answer 2

Obligate: clostridia(梭菌), C. botulinum.
Aerotolerant: lactic acid bacteria.

Question 3

What is the limiting value of water activity for the growth of any micro-organism?

Answer 3

0.6

Question 4

What are the most micro-organisms’ minimum water activities?

Answer 4

Most Gram-negative bacteria 0.97
Most Gram-positive bacteria 0.90
Most yeasts 0.88
Most filamentous fungi 0.80

Question 5

Give examples of antimicrobial components.

Answer 5

Pigments, alkaloids(生物碱), benzoic and sorbic acids(苯甲酸和山梨酸), lysozyme, etc.

Question 6

What is the growth range of bacteria and moulds?

Answer 6

Bacteria around 35 degree

Moulds about 30 degree

Question 7

What are the reactions to CO2 of different micro-organisms?

Answer 7

Moulds and Gram-negative bacteria are most sensitive;
Gram-positive, particularly the lactobacilli, most resistant.
Some yeasts such as Brettanomyces spp. show considerable tolerance of high CO2 levels.

Question 8

Will some form of pre-adaptation decrease the damaging effect of adverse conditions?

Answer 8

Yes