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HDSO Food Science > Lecture 2-Food preservation > Flashcards

Lecture 2-Food preservation Flashcards

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1
Q

How much food is lost to spoilage?

A

25%

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2
Q

What’s a big proportion of the food that is lost to spoilage?

A

Fruits and veggies

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3
Q

__% of landfill in US = food

A

20% of landfill in US = food

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4
Q

What speeds up decomposition?

A

Heat, light and oxygen speed up decomposition

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5
Q

What is lost due to decomposition?

A

Nutritive value is lost

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6
Q

Does food have to be contaminated to be spoiled?

A

No

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7
Q

What is obvious and detectable- decomposition or contamination or both?

A

Decomposition is both obvious and detectable. Contamination isn’t

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8
Q

Why is decomposition obvious and detectable?

A

Due to decreased quality- appearance, taste, texture, odour

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9
Q

Which qualities does the most perishable foods have?

A

High pro or/and water

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10
Q

What are the 3 types of changes that lead to food spoilage?

A
  • Biological
  • Chemical
  • Physical
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11
Q

What are the biological changes in food due to yeast. Uses, actions

A

– Fungus (plant that lacks chlorophyll)
– Ferments sugars (CHO = CO2 and alcohol)
– Used for producing food products e.g. bread and alcohol

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12
Q

Give examples of biological changes in food

A

Yeasts, bacteria, molds

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13
Q

Give examples of chemical changes in food

A

Enzymes (naturally present)

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14
Q

Give examples of physical changes in food

A

Water loss (evaporation/dehydration), separation. damage/mechanical bruisign, tearing of tissues

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15
Q

What are the biological changes in food due to bacteria and molds
Difference between 2, actions

A

– Bacteria and molds can produce toxins
– Molds are visible; bacteria are not
– Bacteria can ferment sugars

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16
Q

How to destroy/inhibit factors behind biological changes in food

A

Boiling, refrigeration, drying, curing (high sugar/salt)

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17
Q

How are enzymes categorsied?

A

Based on substrate and mode of action

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18
Q

What are the 4 modes of actions of enzymes

A

– Protease (proteolytic enzyme): proteins-> AA
– Lipase: TG-> FA + glycerol
– Carbohydrase: CHO -> glucose
– Others (e.g. polyphenol oxidase (PPO))

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19
Q

Talk about proteases in fish

A

Proteases in fish start working straight away

Fish is more susceptible to spoilage

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20
Q

How can you slow down the action of proteases?

A

Cooler temperatures can do that

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21
Q

Downside of dry milk?

A

Lactose in dry milk can react with proteins and create new compounds
Bioavailability of protein in milk is also decreased

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22
Q

What can oxidation of fat lead to?

A

Can lead to off odors and flavors- rancid flavor

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23
Q

What are the non-enzymatic chemical changes in food

A

– Oxidation of fat
– Maillard reaction:
• May occur with long storage of non-fat dry milk (lactose + pro = nonenzymatic browning)
• BV of protein may decr: AA involved in reactions not readily released during digestion

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24
Q

What are the types of separation that cause physical damage?

A

– drip loss E.g. liquid from frozen meat- less moist product
– emulsion breakdown
– syneresis (gel)

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25
Q

Name 6 methods of food preservation

A
  • High temp
  • Low temp
  • Removal/tying up of moisture
  • Additional of chemical preservatives
  • Keeping out microorganisms
  • Ionizing radiation
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26
Q

What do high temperatures do in terms of food preservation?

A

High temperature to destroy microorganisms & enzymes

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27
Q

What do low temperatures do in terms of food preservation?

A

Low temperature to control growth of microorganisms

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28
Q

What do Removal/tying up of moisture do in terms of food preservation?

A

Removal/tying up of moisture to control microbial growth

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29
Q

What do Addition of chemical do in terms of food preservation?

A

Addition of chemical preservatives to inhibit

microbial growth

30
Q

What do ionizing radiations do in terms of food preservation?

A

Ionizing radiations to destroy microorganisms & control enzyme activity

31
Q

How does drying work?

A
  • Removes water in food
  • Inhibits growth of microorganisms
  • E.g. sun-drying or commercial drying
32
Q

Bacteria and mold need __% moisture to survive

Yeast needs __%

A

Bacteria and mold need 15% moisture to survive

Yeast needs 20%

33
Q

What are the commercial ways of drying (4)?

A

• Conventional (uses heat)
– Drying room, tunnel drying, spray drying, drum drying
• Vacuum (uses low pressure)
• Osmotic (uses strong syrup that osmotically gets water out)
• Freeze-drying (ice crystals vaporize)

34
Q

Benefit of vacuum drying

A

Doesn’t have to be heated-integrity is preserved

35
Q

How does freeze-drying work? Benefits?

A 
Most costly- premium products
Ice is taken out instead of water
High preservations of food qualities 
Camping and military rations 
Some instant coffees
36
Q

How does curign work? Uses?

A
  • Preservation with use of salt & drying
  • Sugar, spices, nitrates may be added
  • Meat/fish may also be smoked (for added flavour and preservation)
37
Q

Downside of curing?

A

Overtime microorganisms still multiply. Curing doesn’t stop them, just makes it harder

38
Q

What’s pickling?

A

Preservation by acidification (addition of acid/vinegar OR fermentation)

39
Q

What’s edible coating?

A

A thin layer of edible material (CHO, PRO or FAT) used on fruits, vegetables, cheese, nuts, dried fruit, processed meats…

40
Q

How does edible coating work? (4)

A 
• Increases shelf life
– Barrier to moisture, O2, CO2, volatile aromas
• Improves handling
– Less breaking/damage
• Improves appearance
– By increasing gloss, color
• Vehicle for added ingredients
– Flavours, antioxidants, antimicrobials
41
Q

What are the 2 steps of canning?

A
  1. Food packed into sterilized containers &
    sealed
  2. Containers “canned”/heated to destroy
    microorganisms & enzymes
    – Extended boiling/ heating to temperatures much higher than regular boiling point
42
Q

What are the 2 methods of canning?

A
  1. Boiling water process
    - good for low pH items
  2. Pressure canning
    - for higher pH items
    - boiling at higher temps under pressure
    - to destroy Clostridium botulinum
43
Q

Describe canning for high acid foods

A

For fruits & tomatoes (pH 4.5 or below)
• Safely canned in a boiling water bath
• Heat resistance of microbes is decreased by the acidic pH can be destroyed in reasonable processing times
• Surviving organisms will not grow in acidic environments

44
Q

Describe canning for low acid foods

A

• For vegetables, meat, fish, poultry & milk (pH above 4.6)
• Requires relatively high processing T° to destroy
all spore-forming organisms, particularly C. Botulinum
• Requires a pressure canner where T° > usual boiling point of water can be achieved

45
Q

What are the 3 ways of heat preservation?

A

Boiling
Pasteurization
Ohmic heating

46
Q

Describe boiling as a method of heat preservation

A

Simplest method; 10 minutes

47
Q

Describe pasteurization as a method of heat preservation

A
  • Liquids are heated to a certain T for a certain period of time
  • Eg 71°C (160°F) à15 sec OR 138ºC (280ºF) ->2 sec
  • Kills bacteria, yeasts, molds
48
Q

Describe ohmic heating as a method of heat preservation

A
  • Electrical current passed through food, generating heat that destroys microorganisms
  • Liquid eggs, fruit juices
49
Q

Describe refrigeration as a method of cold preservation. Guidelines

A
  • Slows down biological, chemical, physical reactions that shorten shelf life of food
  • Mostly high water content foods are refrigerated
  • Temperature: just above freezing to ≤ 4ºC
  • Refrigerate perishable foods as soon as possible, preferably during transport to prevent bacterial growth
50
Q

Describe freezing as a method of cold preservation. Guidelines, problems

A

• -18ºC(0ºF) or lower = least damaging to flavor
• H2O unavailable to microorganisms
• Slows chemical & physical reactions (enzymes…)
• Problems:
– Reactions still continue (O2 present), so shorter life than canned goods
– Recrystallization
– Cell rupturing
– Fluid loss
– Freezer burn

51
Q

Dispersion medium in most frozen foods is ___

A

Dispersion medium in most frozen foods is water

52
Q

Benefits of rapid freezing

A

ice crystals are small and numerous, mostly intracellular -> gives superior food quality

53
Q

Downsides of slow freezing

A

ice crystals are large and fewer in number, form in extracellular spaces
– Upon thawing, loss of juices occurs

54
Q

What is freezer burn? Why does freezer burn occur?

A

– Dehydration on the surface of frozen food (white or greyish patches)
– Inadequate packaging-> water evaporates and may recrystallize on surface of food

55
Q

What may happen when plant tissues freeze?

A

Oxidation of polyphenolic substances in plant tissues by polyphenolases may occur during frozen storage

56
Q

What is the downside of oxidation of plant tissues upon freezing? How can that be resolved?

A

– Results in undesirable browning

– Blanching vegetables -> destroys enzymes that cause browning

57
Q

How can ascorbic acid oxidation during frozen storage be resolved?

A

Blanching vegetables inhibits ascorbic acid oxidation by inactivating ascorbate oxidase
However, some loss of ascorbic acid occurs during the blanching process

58
Q

Additional ascorbic acid is lost with ___ ___ of frozen storage

A

Additional ascorbic acid is lost with long periods of frozen storage

59
Q

What are the changes in colloidal substances

during frozen storage (5)

A 
• Retrogradation of starch & syneresis
• Toughening of cellulose
• Breaking of emulsion
• Nutritive value: no significant effects on macronutrients unless food kept for a long time
• Vitamins & minerals: 4% loss in drip
- Vit C, Vit B (especially folate)
60
Q

Why does development of off-odors occur in frozen vegg?

A

Accumulation of volatile carbonyl compounds in unblanched or under blanched frozen vegetables

61
Q

How does blanching before freezing, using boiling water or steam can resolve the problem of development of off-odors in frozen vegg? Downsides?

A
  • Destroys enzymes responsible for development of “off ” flavors
  • Controls undesirable changes in texture & color
  • Inhibits conversion of bright green chlorophyll to olive green pheophytin
  • But destroys some vitamin C and folate
62
Q

What is another name for irradiation?

A

Cold pasteurization

63
Q

What does irradiation do for spices and seasonings?

A

Reduces microbial load on spices and dehydrated seasoning preparations, meaning it destroys bacteria, molds and yeast which cause food to spoil

64
Q

What is the purpose of irradiation do for wheat, flour and whole wheat flour?

A

To control insects in wheat, flour and whole wheat flour

65
Q

What is the purpose of irradiation do for potatoes and onions?

A

To increase shelf life by preventing sprouting or germination in potatoes and onions

66
Q

What is approved by Health Canada for irradiation?

A

potatoes, onions, wheat, flour, whole wheat flour, whole and ground spices, dehydrated seasoning preparations and fresh and frozen raw ground beef

67
Q

How is food irradiation done?

A

foods are treated with low doses of Gamma rays, x rays or electrons

68
Q

What is aseptic packaging? At what temp can it be stored?

A

– Sterilized, packed and sealed in sterilized container under sterilized conditions
– Can sit at room temp

69
Q

Give examples of aseptic packaging

A

Juice boxes, puddings, baby foods, UHT milk

70
Q

How is MAP achieved and what is it used for?

A

– Composition of surrounding air is changed (usually decr
O2, incr CO2 – but depends on food product)
– Fruits & Veg, meat/poultry, baked goods

71
Q

What are hermetically sealed foods?

A

foods that have been packaged airtight by a commercial sealing process

HDSO Food Science (17 decks)

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