Microbiological aspects of food technology

Question 1

What are the three roles of bacteria, yeasts and fungi?

Answer 1

• They can cause a health treat
• They play a beneficial effect (fermentation)
• They can bother us

Question 2

What are the basic forms of bacteria?

Answer 2

Spheres (coccus), rod-shaped (bacillus) and curved types.

Question 3

On what is the classification of bacteria based?

Answer 3

The shape, cell wall composition, presence of the enzymes catalase and oxidase and the breakdown of sugars, amino acids, proteins, starch, etc.

Question 4

What’s the difference between Gram-positive and Gram-negative?

Answer 4

The cell wall of Gram-positive bacteria contains much larger amounts of murrain (peptidoglycan layer) Tham Gram-negative cell walls.

Question 5

What do molds form?

Answer 5

A network of tubular branching hyphae (mycelium)

Question 6

What kind of microorganisms are molds?

Answer 6

aerobic microorganisms which reproduce by the formation of spores using sexual or asexual reproduction.

Question 7

What are the three classes of the fungal kingdom?

Answer 7

• Zygomycetes (molds)
• Basidiomycetes (mushrooms/also yeasts)
• Ascomycetes (largest class, contains yeasts and molds)

Question 8

through which routes can secondary contamination occur?

Answer 8

• The layout of the production plant, apparatus, and equipment
• people (hands, hair, saliva)
• water
• air
• animals
• packaging

Question 9

What is considered the spoilage level?

Answer 9

A concentration of 106 yeasts or 107 bacteria per gram/mL

Question 10

Which four scenarios may occur when microorganisms contaminate a product?

Answer 10

growth, inactivation, dormancy, lethal stimulation

Question 11

What are the phases of the growth curve of bacteria?

Answer 11

1. Lag phase
2. exponential phase
3. stationary phase
4. decay phase

Question 12

Name factors by which the growth of microorganisms is affected

Answer 12

• intrinsic factors: the physical and chemical characteristics of a product
• extrinsic factors: the storage conditions
• impliciet factors: the physiological properties of the microorganism
• process factors: pasteurization, mixing, irradiation

Question 13

What is a rule of thumb with aw and microorganisms

Answer 13

Gram-negative bacteria are most susceptible
to a low aw, followed by Gram-positive bacteria, and the yeasts and fungi are most robust to low-aw environments. Most bacteria prefer a high aw(>0.94)

Question 14

what are the values for HMF, IMF, LMF?

Answer 14

HMF: aw>0.85
IMF: aw 0.7-0.85
LMF: aw <0.7

Question 15

What are the general pH growth limits for microorganisms?

Answer 15

bacteria: 4-9
yeasts: 1.5-8
fungi: 1-11