Lecture 23: Thermal processing and Food Quality

Question 1

Describe the process of blanching

Answer 1

Generally, Blanching is carried out for a specific time (1-15
mins) at below 100 °C (70 to 100 °C) using hot water at or
near atmospheric pressure (Hot water blanchers).

Question 2

What is the objective of blanching?

Answer 2

Inactivate undesirable enzymes

Question 3

What is under blanching?

Answer 3

When foods are blanched, but not at high
enough time/temperatures to deactivate enzymes

Question 4

Why is under-blanching a risk?

Answer 4

• Enzyme are released from disrupted tissue without inactivation
• Cause accelerated damage by mixing enzyme with the substrate during subsequent storage

Question 5

Describe pateruization

Answer 5

Heat treatment (mild thermal treatment: T < 100 °C) given to liquid foods to extend shelf life
* Applications: normally for treatment of liquid foods

Question 6

What is the main objective of pasteurization?

Answer 6

inactivate pathogens, some spoilage organisms & enzyme

Question 7

Define Heat Sterilization

Answer 7

Severe thermal treatment, with T > 100o C
 121o C: commercial sterilization (in-container)
 130-150o C: ultra-high-temperature (UHT + aseptic filling)
* Sufficient high T & sufficient long time
 completely destroy vegetative microbial cells and spores
 completely deactivate enzymes
 commercial sterility at ambient conditions, ready for
consumption

Question 8

How does blanching affect foods?

Answer 8

• Cellular structure
• Pigment change
• Textture change
• Nutritive value
• Loss of vitamins

Question 9

Explain how blanching affects:

Cellular structure

Answer 9

• physical and metabolic changes wihtin cells
  -damages cytoplasmic and other membranes = loss of turgor
• leaching = nutrient losses
• cell death
• removal of inter-cellular gasses