Lecture 6

Question 1

elimination by removal or killing or all microorganisms and the inactivation of viruses present in a product

Answer 1

sterilisation

Question 2

Reasons for sterilisation

Answer 2

• many fermentations must be absolutely devoid of foreign organisms
• Foreign organisms can produce harmful products which may inhibit the growth of the production organisms
• economic penalty is high for loss of sterility
• Vaccines must have only killed viruses
• Recombinant DNA fermentations: exit streams must be sterilised

Question 3

Sterilisation methods

Answer 3

• chemical
• irradiation
• filtration
• thermal

Question 4

→ ethylene oxide (gas) for equipment
→ 70% ethanol-water (pH=2) for equipment/surfaces
→ 3% sodium hypochlorite for equipment

Answer 4

Chemical sterilisation

Question 5

→ ultraviolet for surfaces
→ X-rays for liquids (costly/safety)

Answer 5

Irradiation sterilisation

Question 6

→ membrane filters having uniform micropores
→ depth filters of glass wool

Answer 6

Filtration sterilisation

Question 7

• Dry air or steam can be used as the heat agent.
• Moist (wet) steam can also be used as the heat agent
  (eg: done at 121oC at 2 bar).

Answer 7

Thermal sterilisation

Question 8

Death rate of moist cells are ____ than that of the dry cells since moisture conducts heat better than a dry system

Answer 8

higher

Question 9

Death rate of moist cells are higher than that of the dry cells since moisture conducts heat ____ than a dry system

Answer 9

better

Question 11

Moist steam is ____ effective than dry air/steam

Answer 11

more

Question 12

does not contaminate the medium of equipment that was sterilised

Answer 12

thermal sterilisation

Question 13

Thermal sterilisation using dry heat

Answer 13

• direct flaming
• incineration
• hot air oven

Question 14

Kinetics of cell death equation

Answer 14

kd = Ad e^(-Ed/RT)

Question 15

varies according to the intended use of the product

Answer 15

desired sterility assurance level (SAL)