Physical methods to preserve food

Question 1

Physical methods are the most common in food preservation: TRUE OR FALSE

Answer 1

TRUE

Question 2

What are the 6 physical methods for food preservation?

Answer 2

• High-temperature treatment (cooking)
• Low-temperature preservation (freezing)
• Decreasing water availability (drying, salting)
• Ionizing irradiation
• High-Pressure Processing (HPP)
• Pulsed Electric Field (PEF)

Question 3

What happens when the temperature exceeds the optimal temperature for an organism ?

Answer 3

Cell multiplication slows and eventually stops, additional temperature may result in cell death

Question 4

Factors affecting heat transfer

Answer 4

1) Product Type: Liquids absorb heat faster than solid foods.
2) Container Material: Glass containers heat more slowly than metal containers
3) Container Shape: Tall and narrow containers heat more quickly than other shapes
4) Container Size: The center of small containers get reached more quickly than the center of large containers
5) Agitation: Agitation and mixing help to increase heat transfer especially in viscous or semi-viscous products
6) Temperature of Heating Medium: The greater the difference in temperature between the heat transfer medium and the product, the more rapid the rate of heat transfer to the product

Question 5

What do survivor plot depict ?

Answer 5

the logarithmic nature of population inactivation over time

Question 6

What is decimal reduction time (D-value) ?

Answer 6

as the time it takes of a 10-fold reduction in the number of survivors at a given temperature

Question 7

The D value of a microorganism (decreases/ increases) as the processing temperature increases?

Answer 7

decreases

Question 8

D value is plotted against temperature, it is known as a ___________, it is generally linear

Answer 8

thermal resistance plot

Question 9

The ___________ represents the change in temperature required to change the D value of a microorganism by an order of magnitude (10-fold)

Answer 9

z -value, large z value indicates a more heat resistant organism

Question 10

The _______ is the time, in minutes, at a specified temperature, required to achieve a targeted reduction in a homogeneous population having a specific z value

Answer 10

F-value

Question 11

F-value is important in __________

Answer 11

the commercial canning industry

Question 12

What is the key pathogen of concern for canned low acid foods

Answer 12

Clostridium botulinum

Question 13

Sterilization vs commercial Sterilization

Answer 13

Sterilization: Sterilization is the process of rendering a product free of any living organisms

Commercial Sterilization: Commercial sterility of food products is the application of heat that renders the food free of:

1) Microorganisms capable of reproducing in the food under normal non-refrigerated storage and distribution temperatures
2) Viable microbial cells or spores of public health significance
* Commercially sterile foods are heat treated just enough to produce a safe and shelf-stable product

Question 14

Water can be bound by:

Answer 14

• Hydroxyl groups
• Carbonyl and amino groups of proteins
• Salts

Question 15

Formula for water activity

Answer 15

aw= P/P0

-For pure water, aw = 1.0

Question 16

aw is directly related to the equilibrium relative humidity (ERH) in the air surrounding the food:

Answer 16

ERH (%) = aw x 100

Question 17

High-moisture Foods

Answer 17

Foods with aw above 0.9, foodborne microbes can readily grow in these foods

Question 18

Intermediate-moisture Foods

Answer 18

Foods with an aw 0.65-0.90, such as raisins or jam, because of the moderately low aw these foods are relatively resistant to microbial spoilage (think of how long a jar of jam will last in the fridge)

Question 19

Dry foods

Answer 19

Foods with an aw < 0.65, such as milk powder or crackers, these foods do not support the growth of foodborne microorganisms and have a very long shelf life

Question 20

What type of food is maple syrup

Answer 20

intermediate-moisture food

Question 21

How is maple syrup prepared?

Answer 21

by boiling the sap from sugar maple trees until the boiling temperature is 4.1C higher than that of pure water (which will vary based on air pressure but is around 100C)

Question 22

_________ has the lowest water requirements and can grow with an aw of >0.86. However, it cannot produce toxins at this level

Answer 22

Staphylococcus aureus

Question 23

Yeasts have higher or lower aw requirements compared to bacteria?

Answer 23

Lower

Question 24

_________ are xerotolerant and grow at lower moisture contents than the other types of spoilage microorganism

Answer 24

Molds

Question 25

Molds can produce __________, but ________ production is restricted under xerophilic conditions

Answer 25

Mycotoxins

Question 26

How does glycerol act as a humectant to lower aw ?

Answer 26

glycerol can permeate the bacterial membrane and may have a different inhibitory effect than that of sodium chloride or sucrose.

Question 27

What does Pulsed Electric field eliminate?

Answer 27

vegetative bacterial cells

Question 28

PEF processing is designed to treat what type of food?

Answer 28

pumpable food and involves the application of a short burst of high voltage to a product between two electrodes

Question 29

Drying

Answer 29

the process of mobilizing water present in a food matrix to its surface and then removing it from the surface by evaporation. It often involves simultaneous heat and mass transfer. Most drying operations involve converting liquid water in the material to vapor and then removing it by passing hot air over the product (i.e. beef jerky).

Question 30

Freeze-drying

Answer 30

During freeze-drying the product is frozen first and the moisture is removed via sublimation. Freeze-drying has a minimal impact on the structure and flavor of the food compared with other drying techniques, but has a relatively high cost, and is therefore used as a value added technique (i.e. camp dinners, instant coffee, infant formulas).

Question 31

Osmotic dehydration

Answer 31

is a procedure that involves removing water from fresh food using a hypertonic solutions (sucrose, salts, glycerol). It relies on the ability of the food cells to selectively permit the passage of water out of the food without allowing surrounding solutes to enter these cells. As a result food is dehydrated. It cannot remove all the moisture from the food, so it is mainly used as a pretreatment to other methods of dehydration. Primarily used for dehydrating fruits and vegetables (apples, blueberries, pineapples, mangoes etc.).

Question 32

Electromagnetic radiation with _______ wavelengths (gamma radiation) has lethal effects on microorganisms

Answer 32

shorter

Question 33

Longer wavelengths (microwaves) just generate _____ and are not as effective

Answer 33

heat

Question 34

Ionizing radiation includes _____ and _____ radiation

Answer 34

X Rays | gamma

Question 35

___________ is the primary target of ionizing radiation

Answer 35

The cell’s DNA

Question 36

the smaller the genome, the ______ the resistance to ionizing radiation

Answer 36

greater

Question 37

How is DNA caused in Ionizing Radiation?

Answer 37

By the reaction of reactive oxygen species that are generated during radiation

Question 38

How are X rays produced?

Answer 38

When an electron beam strikes a metal (tungsten or stainless steal)

Question 39

X-ray sources used to irradiate food are restricted to maximum energies of ______ or less, which is effective at treating fresh fruit and vegetables for microbial lethality

Answer 39

5MeV

Question 40

Drawback is that X-rays have ______________________

Answer 40

a high power requirement, and have a high requirement for cooling treatment (most of the energy is lost as heat)

Question 41

In gamma radiation, the radiation sources used for food are : (2)

Answer 41

cobalt-60 and cesium-137

Question 42

What are the advantages or gamma radiation?

Answer 42

- high penetration power - energy is constant over the duration of the treatment - continuous source that doesn't need to be turned off

Question 43

The process of gamma radiation usually consists of exposing

Answer 43

exposing the prepackaged food material to a radiation dose for a certain time

Question 44

Gamma radiation is emitted by:

Answer 44

an excited nucleus of a radioisotope, which permits the nucleus to go to its lowest energy or ground state

Question 45

Redappertization:

Answer 45

-involves a high dose (10-75 kGy) to produce commercial sterility

Question 46

Radicidation:

Answer 46

-involves medium dose (1-10 kGy) to produce the equivalent of pasteurization effect - effective against vegetative bacteria but spores are not inactivated

Question 47

Radurization:

Answer 47

-involves low dose irradiation (0.05-1.0 kGy) to control the presence of insects in grains or stop the sprouting of potatoes or fruit ripening

Question 48

HPP involves:

Answer 48

treating food with pressures in the range of 100-600 MPa which will inactivate most bacteria, yeasts, molds and viruses (spores survive)