Ch 21: Thermal destruction of Microorganisms

Question 1

Reasons for heating foods

Answer 1

• Reduce/destroy microbial activity
• Inactivate enzymes
• Shelf stable foods
• Indice desired chemical/physical rxns

Question 2

Factors that affect microbial growth

Answer 2

• Temp
• pH
• Water activity
• Oxygen

Question 3

Define: Aerobes, Anaerobes and Faculative Anaerobes

Answer 3

Aerobes - oxidized conditions
Anaerobes - cannot tolerate O2
Facultative anaerobes - adaptable - prefer aerobic but can grow in anaerobic

Question 4

What is the difference between Intoxication and Infection

Answer 4

Intoxication: a toxin pre-formed by microbes prior to injestion
Infection: the live microorganism is ingested to cause disease

Question 5

Which factors should be considered when determining the extent of heat treatment?

Answer 5

1. Heat resistance of microbes
2. Rate of heat penetration into food
3. heating conditions
4. pH
5. Type of container (size/shape etc)
6. Thermophysical properties of foods
7. Storage conditions following process

Question 6

Microbial destruction follows ____ kinetics

Answer 6

First order

Question 7

Determine the thermal destruction rate of the test microbe under the conditions that ____

Answer 7

normally prevail in
the container and the processing situation

Question 8

Define D-value

Answer 8

Decimal Reduction TIme: Time taken to reduce the microorganisms by one
log cycle (90%) at a given temperature is defined as D-value.

Question 9

Units for D-value:

Answer 9

Time: minutes

Question 10

D value ____ when temperature ____

Answer 10

Decreases
Increases

Question 11

Define the phantom thermal death time (TDT)

Answer 11

curve for a microorganism is obtained by plotting log-transformed D values vs. temperature

Question 12

Define z-value

Answer 12

Thermal resistance constant: Temperature difference in °C to change the D-value by 1 log cycle (90%). Describes the influence of time of the D value for microbial populations

Question 13

Define F value

Answer 13

It is the number of minutes
required to kill a known population of microorganisms in a given food under specified condition (e.g., 121.1 °C).

or

the total time required to cause a given decimal
reduction of a microbe population at a given T.

Question 14

Define Sterilizing value (SV):

Answer 14

Sterilizing Value (Lethality): number of log reductions

Question 15

Define Fo

Answer 15

is number of minutes required to destroy a specified number of microorganisms at 121.1 degree C when z is 10 degree C.