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HDSO Food Science > Lecture 3 > Flashcards

Lecture 3 Flashcards

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1
Q

What is the chilling storage temp range?

A

<15C to >0C

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2
Q

What are commercial values of chilling?

A

4.4-7C

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3
Q

What does chilling do?

A

Slows:
Growth of Micro-organisms except Psychrophile

Metabolic Activity of plant and animal tissues

Chemical Rxn: Enzyme Catalyzed Oxidation

Moisture Loss
-dont become wilted

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4
Q

What is a controlled/modified atmosphere?

A

Decrease O2 to 3-5% and Increase CO2 to 3-5%

Modified Atmosphere slow down Aerobic Respiration

Decrease this by decrease O2 or temp
lower rate of respiration lower spoilage

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5
Q

What is the composition of air?

A

Air is composed of 78% N and 21% O2

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6
Q

In chilling storage, do we want to remove all the O2?

A

No, because that would result in anaerobic respiration which may produce toxins and alcohol.

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7
Q

What does chilling storage promote?

A

Cold Shortening of Animal Muscle (Meat toughness)
-Muscle are contracted=toughness

Chilling Injury of Fruit/Vegetables (Apple softness)

Chill Sweetening in Potatoes
-Accumualtion of sugars in potatoes and result in access browning when you fry the potatoes

Staling of Bread

  • Bread firmness due to Retrogradation
  • (Re-arrangement of Amylose and Amylopection)
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8
Q

What is happening to leftovers in the refrigerator?

A

1) Slow microbial growth

2) Enzymatic changes that may cause off-flavour

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9
Q

What do you think are the most important factors

A

1) Refrigerate foods ASAP
2) Pack foods in small portions
3) Avoid cross contamination

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10
Q

Fruits and vegetables coming into storage are usually contaminated, especially with mold spores, sure or false?

A

True

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11
Q 
What kind of deterioration are the enzymes 
Lipoxygenases
Lipases			
Proteases 
Responsible for?
A

Off-Flavour
(Rancidity)

• Affect protein, and can breakdown protein and lipid structure

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12
Q

What kind of deterioration are the enzymes
Pectic Enzymes
Cellulase
Responsible for?

A

Off-Texture
Excess Tissue Softening

• Affect cellulos and pectin,

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13
Q 
What kind of deterioration are the enzymes 
Polyphenol Oxidase
Chlorophyllase		
Peroxidase   
Responsible for?
A

OFF-Colour

Discolouration

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14
Q

What kind of deterioration are the enzymes
Ascorbic Acid Oxidase
Thiaminase
Responsible for?

A

Nutrient Loss

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15
Q

What are the optimal temperatures for chilled storage of meat and dairy?

A

Fresh Meat and Fish
1 to 1C

Dairy 0.5C

Cooked Meats and Fruits 2 to 8C

Typical Home Refrigerator
4 to 8C

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16
Q

What are the other factors that affect shelf-life?

A

Light
Pasteurization
Waxing or Oiling
Controlled Atmosphere

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17
Q

Why does light affect shelf life?

A

Promote Sprouting of Potatoes, Onions

Store in dark dry and cold environment to inhibit sprouting

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18
Q

Why does pasteurization affect shelf life?

A

Pseudomonas fluorescens????

  • Spoilage bacteria
  • HEAT Resistant, not destroyed by pasteurization

Spoilage bacteria that casues slimelyness in dairy, is heat resistant (not destroyed by pasteurization

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19
Q

Why does waxing or oiling affect shelf life?

A

Decrease Dehydration: Fruits/Vegetables

Decrease Dehydration and CO2 losses : Eggs
-CO2 when inside of the egg regulates the pH, whe Co2 is lost pH increases and the whites make it more runny

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20
Q

Why does a controlled atmosphere affect shelf life?

A

Decrease Aerobic Respiration
-Decreasing rate of spoilage

Decrease M.O. Growth
-Especially those that are aerobic

Decrease Oxidation
-Less rancidity

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21
Q

What are the temperatures for freezing?

A

Freezing: Optimum Temperature for Home Freezing: -18oC

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22
Q

What is crystallization?

A

The formation of systematically organized solid phase from solution

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23
Q

What does freezing consist of?

A

1) Nucleation: Site for Crystal Growth (Seed Formation is association of molecules into tiny ordered particles)
2) Crystal Growth: Enlargement of Nucleus

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24
Q

What does freezing do?

A

Decreases Water Activity (aw)

Reduce Microbial Activity

Reduce Rate of Chemical Reactions

(i.e., Lipid Oxidation)

Less free water thee less activity and can result in less microorganism activity

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25
Q

What are the 2 kinds of ice crystal formation?

A

Slow and fast freezing

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26
Q

What us the difference between the 2 kinds of ice crystal formation?

A

Slow Freezing (H2O molecules have enough time to migrate to seed crystals)

  • Large Ice Crystals
  • Not Desirable
  • Home freezer
  • Result in few large crystals, hase more time to igrate to other seed crystals

Fast Freezing known as Cryogenic Freezing

  • Small Ice Crystal
  • Desirable
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27
Q

If freezing stops growth of bacteria, why does frozen foods have a best before date?

A

1) Quality
2) Sensory Properties
- Enzymes are stiill active

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28
Q

Freeze Concentration can increase the concentration of enzymes and their substrates and result in faster reaction rates, true or false?

A

True

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29
Q

What are the advantages of rapid freezing?

A

Formation of a large number of small ice crystals that are evenly distributed

Less damage to tissue

Lower movement of soluble component within food b/c time of solidification is short
-Soluble component= sugars and salts

Reduction in rate of chemical Rxn.

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30
Q

What are the ways that quality of the product can deteriorate during freezing?

A

Drying Out: Freezer Burn (poor packaging)
-Still safe to eat just sensory qualities decrease

Lactose Crystallization> Sandiness of Ice Cream
-Whe there is a flux in temp when storage

Loss of Volatile Components
-Are lost during storage

Protein Denaturation > Toughness of Meat

Oxidation of Vitamin C, Thiamin, Riboflavin

Oxidation of Fat > Rancidity

Colour Change: Degradation of Chlorophyll
-Decrease green colour in vegetables

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31
Q

What is recrystallization?

A

Unstable Crystals> Metamorphic Changes
Change in #, Size, Shape
Change in Orientation

Is not desireable because sensroy properties are going to be damaged

32
Q

What are the possible reasons for recrystallization?

A

Increased Temp. or Fluctuating Temp.

33
Q

What is the freezing curve for Water?

A

A- S: Cooling- No : H20> Ice Transformation

S-B: Temp- Release Heat of Crystallization
-First ice crystals are formed at point B ith initial freezing point

B-C: Major Portion of H20 Crystallized

C: Eutectic Point: Solutes Freeze

C-D: More Crystallization

34
Q

What is thawing, how should we do it?

A

Time Consuming

Loss of Quality: Enzymatic and Microbial Activities

Recommended Condition for Thawing is either Temp < 7.2oC or under Running Cold Water

Freeze Food in Small Packages >Thaw Faster

35
Q

What is the thermal conductivity of ice?

A

Thermal Conductivity of Ice is 4 Times Greater than Water

Freezing:

  • Ice Layer Expanding
  • Ice Transmits Energy Rapidly
  • Solid phase expanding in freezing

Thawing:

  • H20 Layer Expands
  • H20 is a Better Insulator
  • Liquid layer is expanding and water is less thermo conductive
36
Q

What are the different methods of freezing?

A

Air blast freezing (most common)
Plate freezing
Liquid Freezer
Slow freezing

37
Q

What is air blast freezing?

A 
Some foods are packaged first
Placed on racks
Send into insulated tunnel 
	(-30oC, -40oC)
Cold Air is blown over them (500-1500 ft/min)
Peas are frozen first-> then Packaged 
 -(will result in 5% moisture loss)
38
Q

What is plate freezing

A

-Foods are packaged
Sandwiched between metal plates (Full contact with the products)

Temperature: -34C

39
Q

What is liquid freezer?

A

Liquid Nitrogen: Flash Freezing
Liquid CO2: Quick Freeze

Cryogenic liquids are liquefied gases of extremely low boiling point (b.p.)

High quality frozen product

Individual food portion is sprayed with liquid N2

40
Q

What temp does liquid CO2 and N2 boil at?

A

CO2: -79C

N2: -196C

41
Q

What are the advantages of liquid N2?

A

B.P. = -196oC
(Great driving force for heat transfer)

Intimate Contact (Irregular shaped foods)

Nontoxic and Inert

Replaced 02, Lower oxidation

Fast: High Quality

42
Q

What are the disadvantages of liquid N2?

A

high cost

Some safety issues

43
Q

The speed of liquid-nitrogen freezing produces frozen foods with a quality unattainable by non-cryogenic freezing methods true or false?

A

True

44
Q

In Cryogenic liquids, cold temperature results from______ of liquid nitrogen or CO2.?

A

Evapration

45
Q

Some products such as mushrooms cannot be frozen by other methods without excessive tissue damage, true or false?

A

True

46
Q

What is slow freezing?

A

Fruits, Fish

Cold Room: -23oC, to -34oC with some air circulation

Glaze Formation (Coating of ice prevents dehydration)
-Dip fish in water than put in freezer to have a thin layer of ice in fish to prevent dehydration
47
Q

Why is blanching used as a pre treatment method for freezing?

A

Mild heat process To inactivate enzymes (Catalase and Peroxidase)
-Indicator enzymes for blanching

To destroy some microorganisms

To fix colour of green vegetables

48
Q

What temp should you keep frozen things at?

A

-18C or lower

49
Q

Why is -18C for frozen things too strict?

A
  • Food pathogens do not grow below 3.3oC

- Food spoilage does not happen below -9.5oC

50
Q

What is the reason for choosing -18oC for freezing?

A

Enzymes are very resistant to cold temperature and may stay active at even -18oC.

51
Q

What are the factors of determining the freezing rate?

A

1) Driving Force
- The temperature difference between the product and the cooling medium

2) Resistance to heat transfer, which depends on:
- Air velocity
- Thickness of product
- Composition of the product

52
Q

What is the order of chemical comp and thermal conductivity?

A

Air

53
Q

What are the 3 stages of deterioration changes?

A

Freezing
Frozen
Thawing

54
Q

What impact does freezing have on microorganisms?

A

Microbial Changes: Few Will Die, Many Survive

Physical Changes: Ice Crystals Rupture Cells

Chemical Changes: Freeze Concentration

55
Q

What impact does frozen storage have on microorganisms?

A

Microbial: M.O. Survive but most Do Not Grow

Physical: Colour Changes, Re-Crystallization, Dehydration

Chemical: Enzymatic RXN (Lipoxygenase) and Oxidation of Vit. C

56
Q

What impact does thawing have on microorganisms?

A

Microbial
Some Growth

Physical
Ice Crystals Start to Melt (Solid Liquid)

Chemical
Enzymatic RXN.

57
Q

Why are packaging materials important?

A

The resistance to heat transfer of the food package depends on:

The more direct contact between food and cold medium > Higher Freezing Rate

58
Q

What makes a good packaging for freezing?

A

Resistant to the permeation of water vapour to inhibit dehydration

Strong and Flexible

Protective against light and air

Liquid-tight to prevent leaking on thawing

59
Q

What are some packaging materials?

A

Plastic bags
Aluminum foil wraps
Plastic wrap
Waxed paper

**Glass is not recommended due to breakage from expansion during freezing

60
Q

Freezing and frozen transportation and storage are highly energy intensive and ______?

A

Costly

61
Q

What are other methods of processing that may yield products equal or nearly equal in quality to those obtained by freezing?

A

Concentration followed by freezing (Orange Juice).

High Temp. Short Time (HTST) followed by aseptic packaging

Irradiation

62
Q

What is concentration?

A

The removal of H20

Advantages: Easier Transport and Storage

63
Q

What is evaporation?

A

Heating liquid to the Boiling Point to remove H20 as vapour

64
Q

What are the different ways you can concentrate something?

A

Evaporation

Vacuum Evaporation

Reverse Osmosis (RO):

Partial Freezing and Removal of Ice Crystals

65
Q

What is reverse osmosis?

A

Applying a mechanical force which exceeds the osmotic pressure, H20 moves in reverse direction

By applying a mechanical force which exceeds the osmotic pressure, H20 moves in

reverse direction

66
Q

What is the purpose of evaporation?

A

Volume reduction (juices, cheese whey)

Preparation of conc. foods (syrup, sauces)

Preparation of dehydrated foods

Preservation (intermediate H20: 20-50%)

67
Q

How can you concentrate heat sensitive liquids?

A

Evaporate under vacuum (Lower Temp.)
-Don’t have to heat it as much

Membrane Separation (M.S.)
-To remove excess water
68
Q

What is the membrane separation process?

A

The principal Membrane Separation processes; in order of pore size:
-Separate Particles based on size as follows:

µF UF RO
0.1-10µ .01-0.1µ 0.001µ

Micro, ultra filtration and reverse osmosis

69
Q

What are the advantages of membrane separation?

A

Same equipment can be used for different processes and purposes

70
Q

What is the difference between Micro, ultra filtration and reverse osmosis ?

A

RO only lets water filter through

Ultra lets water and sugars and low molecular weight compounds

71
Q

Why is reverse osmosis used?

A

useful in small scale operations

As a substitute for evaporation
-NOT suitable for some products

Pre-Concentration before evaporation
-More energy efficient

72
Q

What products can be made with reverse osmosis?

A

Juice Concentration
Concentration of Grape Juice: Wine Making
Cheese whey Concentration
Desalination of Sea Water

73
Q

Why is ultra filtrate used?

A

*Concentration of proteins in cheese whey

Clarification of wine

74
Q

Why is microiltrate used?

A

Permeable to all solutes, but not to colloidal materials or particles such as Precipitated Protein & Pectic Substances

Clarification of juices and wines
-Remove suspended particles & Precipitated Proteins

75
Q

What products are used in micro filtration?

A

Cold Pasteurization of Beer (Draft Beer in bottles)
-Remove Microorganisms

Remove Spore Forming Bacteria that produce gas during ripening of cheese
-(Dutch and Swiss style cheeses)

HDSO Food Science (17 decks)

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