Physical methods of food preservation

Question 1

Inactivation

Answer 1

the destruction of the organisms as judged by its inability to recover on microbiological media

Question 2

which method of food preservation is most common?

Answer 2

physical methods

Question 3

purpose of food preservation

Answer 3

• extended shelf life

- ensure food safety by inactivating pathogens or preventing their growth

Question 4

High temperature treatment

Answer 4

• temperature exceeds the optimal temperature for an organism. The cell multiplication slows and eventually stops.
• additional temperature may result in cell death - denaturation

Question 5

why is heat treatment effective

Answer 5

it can eliminate almost any microbial target and is customizable to the product and organism of concern.

• Risk: overheating may damage the product quality
• Major parameters: temperature and time

Question 6

Heat transfer - what factors affect it (6)

Answer 6

1. product type
2. container material
3. container shape
4. container size
5. agitation
6. temperature of heating medium

Question 7

survivor plot

Answer 7

depict the logarithmic nature of population inactivation over time

Question 8

decimal reduction time (D value)

Answer 8

the time it takes of a 10-fold reduction in the number of survivors at a given temperature
-the greater the D value at a given temp, the more resistant that organism is to heat

Question 9

What happens to the D value when the temperature increases?

Answer 9

the D value decreases

Question 10

thermal resistance plot

Answer 10

when the D value is plotted against temperature (usually linear)

Question 11

z value

Answer 11

thermal resistance constant
(the negative reciprocal of the slope on a thermal resistance plot)
-represents the change in temperature required to change the D value of a microorganism by an order of magnitude (10-fold)
-larger Z value: more heat resistant organism

Question 12

Thermal lethality measurements

Answer 12

taken to determine the amount of time required to commercially sterilize food at a given temperature

Question 13

F value

Answer 13

the time (in min) at a specific temperature required to achieve a targeted reduction in a homogeneous population having a specific z value
-F value is important in the commercial canning industry

Question 14

Difference between D value and F value

Answer 14

D value defines the time it takes to reduce the population by 1 log. F value represents the time it takes to get the population to a specific level (ie 10^1 or sterile)

Question 15

Which organism + what test is used in the canning industry?

Answer 15

• C. botulinum: key pathogen in canned low acid foods.

- use the F value at a specific temperature to achieve commercial sterility.

Question 16

sterilization

Answer 16

• the process of rendering a product free of any living organisms
• ex. autoclaving reders media sterile
• using sterilization would cause the food to become unacceptable quality (through excessive heating)

Question 17

commercail sterilization

Answer 17

food free of

1. microorganisms capable of reproducing in the food under non-refrigerated storage and distribution temperatures
2. viable microbial cells or spores of public health significance
   - ie heat-treated just enough to produce a safe and shelf-stable product

Question 18

Important factor in heat resistnace?

Answer 18

state of dormancy: stationary phase cells are more resistant to heat than exponential phase cells and spore formation dramatically increases heat resistance
-stress: if aw, pH, or antimicrobial constituents are stressing them, less heat will be needed to kill them

Question 19

Aseptic processing

Answer 19

• used in industry where foods and cans are sterilized separately and then foods are packaged under aseptic conditions
• product is heated by passing through a set of heat exchangers until the holding time and temp has been reached.
• passed through cooling exchangers
• used for fruit juices, dairy products, sauces (not particulate containing foods)