Week11C1-2 : thermal processing

Question 1

What are the three basic levels of heat treatment?

Answer 1

1. Sterilization
2. commercial sterility
3. Pasteurization/blanching

Question 2

What is the temperature of sterility and the time

Answer 2

121˚C for 15 minutes.

Question 3

What is the definition of sterility?

Answer 3

means there is no living forms alive or biologically active

Question 4

What is the definition of commercial sterility ?

Answer 4

kill all pathogenic and toxin-forming vegetative organisms.

Question 5

at what temperature is steam if under these pressure :
10 psi :
15 psi :
20 psi :

Answer 5

10 psi : 116
15 psi : 121
20 psi : 127

Question 6

T or F : for low acid foods, the temperature of the food needs to reach temperature higher than 100C

Answer 6

t

Question 7

T or F : the temperature used in pasteurization are over the boiling point

Answer 7

f

Question 8

T or F : the pasteurization and the commercial sterility deactivate spores

Answer 8

false, the pasteurization doesn’t deactivate spores but the commercial sterility does

Question 9

What is the goal of blanching

Answer 9

To denature the enzymes that are deleterious in fruits and vegetables

Question 10

What are the three rules that decides the thermal processing that will be done?

Answer 10

1. eliminating the microorganisms
2. Maintaining the nutritional and sensory qualities
3. Food safety

Question 11

T or F : C. Botulinum is used to evaluate the efficacy of a thermal processes

Answer 11

F, it is too dangerous because it is a dangerous spore and you need to use the more temperature resistant spores

Question 12

What are the two spore former used to evaluate the efficacy of thermal processing

Answer 12

1. Clostridium sporogenes PA3679

2. Bacillus stearothermophilus

Question 13

What is the commercial sterility levels of spores in cans

Answer 13

10^-6 (or 12 log reduction or 12D)

Question 14

What is the D-value?

Answer 14

the deciml reduction time is the heating time required at a given temperature to reduce the microbial population by one log unit.

Question 15

How is the D-value determined

Answer 15

by experimentation of standard plate count of samples that have been heated for different amounts of time

Question 16

What is the thermal death rate curve?

Answer 16

The curve that shows the log reduction of spores against the time for a specific temperature

Question 17

Does temperature affect the thermal death curve?

Answer 17

yes.

Question 18

What is the Z value?

Answer 18

It is the thermal resistance of an organisms and depends on the d-value. The temperature increase corresponding to reduce the D value by one loge or 10 factor

Question 19

What does HTST stands for ?

Answer 19

high temperature short time

Question 20

What are the two types of thermal processing?

Answer 20

1. conventional processing

2. Aseptic processing

Question 21

What is the type of thermal processing that is suitable for the HTST processes

Answer 21

aseptic processing

Question 22

What is the name of the machine used that is a large pressure cooker

Answer 22

batch retort.

Question 23

T or F : the thermal processing using a batch retort is a continuous process

Answer 23

f

Question 24

What is the name of the machine that is u-shaped and used in the conventional thermal processing for canning

Answer 24

hydrostatic cooker and cooler

Question 25

T or F : the hold time of the thermal processing takes into account only the D-value

Answer 25

False, it needs to take into account the come-up and come-down times.

Question 26

Where are placed the thermocouples that measure the product heat

Answer 26

at the cold point

Question 27

What factor influence the location of the cold point in food?

Answer 27

it depends on the type of heat transfer that is predominant in the food. For solids it is conduction and for liquids it is convection

Question 28

Complete : for conduction in heat penetration studies, the cold point will be at ___ of the can

Answer 28

center

Question 29

Complete : for convection in heat penetration studies, the cold point will be at ___ of the can

Answer 29

1/3 up from the bottom

Question 30

T or F : heat tranfer characteristics can change during the thermal processing

Answer 30

true, example for gelatinization will slow down the rate of heat transfer.

Question 31

What is the temperature of pasteurization of milk in the HTST ?

Answer 31

71C for 15 seconds then rapid cooling at 2C

Question 32

What is the temperature for UHT in milk pasteurization?

Answer 32

over 100C for 1 second

Question 33

What is the commonly used method for pasteurization of milk ?

Answer 33

HTST pasteurization with plate heat exchangers.

Question 34

When was developed the UHT processing

Answer 34

1970

Question 35

Since what year do we use the HTST pasteurization

Answer 35

1930

Question 36

What are the three advantages of aseptic processes?

Answer 36

1. continuous 2. Very high and efficient heat transfer rates 3. Not constrained by the container size and shape

Question 37

What are commonly used to sterilize the packaging in the asceptic processing

Answer 37

UV light and hydrogen peroxide

Question 38

What is the temperature and time of batch processing

Answer 38

62,5 for 30 minutes

Question 39

How does heat kill the microorganisms?

Answer 39

by denaturing the proteins and inactivating their enzymes.

Question 40

T or F : the asceptic processing is useful for heat sensitive products.

Answer 40

True, owing to HTST.

Question 41

What is the temperature and time used for commercial sterility?

Answer 41

Depends on the product, but the time should result in a 12log reduction of the microbial load and that depends on the temperature.