Midterm 1.6 Food Processing Slides

Question 1

Food pathogens vs. food poisoning microorganisms vs. food spoilage microorganisms

Answer 1

Pathogens - public health concern, enter the human system via food

Food Poisoning - microorganisms produce toxins that cause illness and harm public health

Food Spoilage - microorganisms that are NOT a public health concern, cause spoilage

Question 2

Common food pathogens (11)

Answer 2

1) Clostridium perfringens, campylobacter jejuni
2) salmonella
3) Escherichia coli 0157:H7
4) Bacillus cereus
5) Listeria monocytogenes
6) Shigella
7) Staphylococcus aureus
8) Streptococcus
9) Vibrio, Yersinia

Question 3

Microorganisms of safety concern (4)
Toxins of concern (2)

Answer 3

1) Clostridium botulinum (neurotoxin producing)
2) Clostridium perfringens
3) Staphylococcus aureus
4) Bacillus cereus

1) Mycotoxin alfatoxin
2) Natural alkaloids

Question 4

Post-harvest causes of spoilage

Answer 4

Respiration - oxidation of organic matter

Transpiration - moisture removal from product (unless 100% RH), prevent temp fluctuations and damage

Ethylene production - flammable, colorless, sweet smelling and suffocating causes ripening in produce

Physiological breakdown - injuries from freezing, heat or sun exposure

Question 5

What is the zone of spoilage in fridge/freezer without danger to health?

Answer 5

-10 to 4.5°C (14 to 40°F)
Below there is no growth, above there is rapid growth

Question 6

Refridgerated storage of plants vs. animals

Answer 6

Phytosystem - aerobic and anaerobic, a need to maintain respiration, softening and heat of respiration

Myosystem - anaerobic, suppress rigor mortis and tenderization

Question 7

Zone of maximal ice crystal formation in freezing food

Answer 7

-2 to -5°C

Because of solutes, temp for freezing changes as it freezes (as solutes increase, freezing temp decreases)

Freezing is faster than thawing because water is a worse conductor of heat than ice

Question 8

Rapid freezing produces

Answer 8

many small ice crystals that cause less damage to cell walls and muscle cells

Question 9

Indirect vs direct forms of freezing

Answer 9

Direct: Air, liquid immersion and cryogenic freezing

Indirect: plate freezing

Question 10

Types of canning retorts

Answer 10

Vertical, horizontal, agitating, water immersion and steam

Question 11

Quality optimization in thermal processing equation

Answer 11

q = kA∆T/x
h = k/x

Question 12

Microwave processing types

Answer 12

MW are oscillating electromagnetic waves
Dipole rotation (water) and ionic polarization (salts)

Question 13

activity of water (aw)

Answer 13

ERH/100 or p/p0
ERH = equilibrium relative humidity
dry below .6 aw

Question 14

Moisture Sorption Isotherms (MSI)

Answer 14

Relationship between Me (Equilibrium Moisture Content) and ERH (Equilibrium Relative Humidity)

Temperature specific

Question 15

Hysterisis

Answer 15

During desorption water is exiting cells, so there is a higher moisture content for the same RH

During absorption there is more free water so the moisture content is lower for the same RH

Question 16

Volume changes in vacuum drying, freeze drying and conventional drying

Answer 16

• Volume increases in vacuum drying (puffing)
• Volume stays the same in freeze drying (no movement of water, freezing + sublimation)
• Volume decreases in conventional drying (water exits cells)

Question 17

High pressure processing

Answer 17

AKA pascalization
400 to 700 MPa for food processing

Isostatic pressure is applied in all directions and so the food stays intact (cells don’t burst because of water turgidity in high water content foods)

Inactivates microorganisms and enzymes but spares covalent bonds (gives cooked appearance of meat)

Reactions resulting volume decrease are accelerated by HPP (volume increase are suppressed)

Question 18

Applications of HPP

Answer 18

Pasteurization, sterilization, texture modification, functional changes and specialty processes (freeze, thaw, fat crystallization and enhancing reaction kinetics)

Question 19

Pulse electric field processing

Answer 19

High voltage electrical short pulse (static or continuous) which perforates cells

For preservation or extraction of low depth samples (usually liquids)

Question 20

Pulsed light processing

Answer 20

Intense broad spectrum pulses of light (5-10), but UV does the work

20,000x the intensity of sunlight

Used for samples where light can pass through or food contact surfaces

Question 21

Strength of radiation waves

Answer 21

Alpha is least penetration
Beta rays next intensity
Highest penetration is gamma rays

Question 22

Ionizing radiation processing and doses

Answer 22

Using Cobalt-60 or Cesium-137 for gamma rays or B-rays (low intensity, not practical)

Radiation doses:
Low (1 kGy) - inhibits sprouting, disinfects insects/parasites and delay ripening
Medium (1-10 kGy) - eliminate spoilage bacteria and extend shelf life
High (10-50 kGy) - decontaminate herbs, spices and food ingredients