Pasteurization/Sterilization

Question 1

Pasteurization is

Answer 1

a heat treatment securing certain destruction of unwanted micro-organisms without impairing the commercial value of the product (mild <100 degrees)

Question 2

Sterilisation is

Answer 2

a heat treatment to destroy all micro-organisms including all bacterial spores

Question 3

Commercial sterilization is

Answer 3

a heat treatment to destroy all micro-organisms (and enzymes) capable of developing in the produt post-processing.

Question 4

What does the severity of the heat process depend on?

Answer 4

• Nature or physical state of the food
• pH value
• Thermal sensitivity of the components
• Hygiene pre-processing i.e. the number and nature of the microbes present
• Thermal resistance of the pathogens

Question 5

The severity of the heat treatment depends mainly on

Answer 5

the pH of the food

Question 6

Low acid food (pH >5.5)

Answer 6

E.g. peas, spinach, meat and fish

Needs to destroy spores of C.botulinum A, C.thermosaccharolyticum, B. stearothermophilus

Question 7

Medium acid foods (pH 4.6-5.5)

Answer 7

e.g. carrots, celery, soups and sauces

C. botulinum cpores slightly less heat resistant

Question 8

Acid foods (pH 3.7-4.5)

Answer 8

e.g. tomato, turnip, pears

Milder process necessary

Question 9

High acid foods (pH <3.7)

Answer 9

e.g. citrus fruit, rhubarb

Spoilage rare but can occur (e.g. byssochlamys fulva)

Question 10

Rigourous heat treatment would cause serious damage to the conductive pack so…

Answer 10

use nitrate, nitrite, chloride - reduces the need for a severe heating so can use milder pasteurisation method

Question 11

What does not cause spoilage?

Answer 11

C. botulinum and C.welchi

Question 12

Spores from spoilage organisms are:

Answer 12

• more resistant to heat and therefore require a more severe heat treatment
• more numerous and therefore require a more severe heat treatment
  Hence if no spoilage (post-processing) can assume pathogen free

Question 13

Can examination post treatment

Answer 13

Incubate samples at both 37 degrees C and 55 degrees C to examine for gas production (due to C. thermosaccharolyticum) flat sours (due to B.stearothermophilus) and anaerobes (including C. nigrificans causes cans to turn black inside)

Question 14

What is the aim of heat preservation:

Answer 14

• To heat food to a sufficient temperature for a sufficient length of time to destroy micro-organisms and enzymes as required for sterilization and pasteurisation
• To prevent re-contamination