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food spoilage and preservation Flashcards

(48 cards)

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1
Q

What are yeasts? Their uses and living conditions.

A

. Eukaryotic, single-celled fungi
. Lives off the sugar present in foods
. Used in bread, but can be harmful at times

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2
Q

where are yeasts found

A
  • Fresh seafood
  • Packaged meats
  • Deli-catessen (ready to eat) salads
  • Plants, soil, water, insects
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3
Q

what do yeasts use to grow

A
  • Carbohydrates (e.g. sugars, pectins)
  • Organic acids (lactic, citric, acetic)
  • Proteins, lipids
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4
Q

What can they tolerate well?

A
  • Low pH (acidic)
  • Low temperature
  • Low water activity
  • Some preservatives
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5
Q

What preservatives can they conquer

A

Can metabolise preservatives like:
- Benzoate
- Propionate
- Sorbate

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6
Q

What are the visual signs that yeast has spoiled food?

A

1- Slime production
2- Pigmented surface growth
3- Off-odours and off-flavours
4- Gas, acid, or alcohol from sugar fermentation

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7
Q

give yeast examples

A
  1. Sac-charo-myces
  2. Sac-charo-myces cerevisiae (baker’s yeast), 3. Crypto-coc-cus
  3. C. neo-for-mans
  4. Candida albicans
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8
Q

how is yeast activated

A

Moisture, food/sugar, time. Room temp warmth.

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9
Q

what happens when yeast gets wet?

A

it releases carbon dioxide

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10
Q

What does yeast spoilage look like?

A

small and defined

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11
Q

What are moulds?

A

Microscopic fungus

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12
Q

How can moulds contaminate food?

A

Tiny mould spores are carried in the air and land on food

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13
Q

How can mould contamination cause illness

A

mycotoxins such as aflatoxins (200+ types)

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14
Q

What does mould contamination look like?

A

Large, diffused, fussy growth.

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15
Q

Name a few examples of moulds.

A

Alternaria, Aspergillus, Botrytis, Cladosporium, Fusarium, Geotrichum,
Monilia, Manoscus, Mortierella, Mucor, Neurospora, Oidium, Oosproa,
Penicillium, Rhizopus and Thamnidium

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16
Q

define food spoilage

A

changes that make food inedible

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17
Q

describe visual spoilage signs

A
  1. Physical Damage: Bruising, crushing, or tearing of food
  2. Microbial Growth: Mould or bacterial colonies
  3. Slime Formation;
    Common in meats and seafood due to microbial action
  4. Insect Damage;
    Holes, larvae, or signs of infestation
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18
Q

how could you evaluate if food is spoilt

A

Mostly sensory, but also supported by biochemical/microbial tests

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19
Q

What are intrinsic parameters

A

Natural food properties:
1. Water activity
2. pH
3. nutrients
4. antimicrobials

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20
Q

What are extrinsic parameters

Study These Flashcards
A

Storage environment:
1. Temperature: Cold slows growth; warmth speeds it up.

  1. Humidity: Moist conditions favour microbial activity.
  2. Atmosphere composition: Levels of oxygen or modified atmospheres (like vacuum or CO₂-rich) can inhibit or promote certain microbes.
21
Q

describe how modes of processing an presentation affect spoilage

Study These Flashcards
A

Processing methods can affect which microbes survive or grow( microflora).
1. Physical treatments: Heating, drying, freezing, irradiation.

  1. Chemical treatments: Addition of preservatives like salt, acid, or sorbate.
22
Q

describe implicit parameters affect on spoilage

Study These Flashcards
A

These are interactions between microorganisms themselves. The growth of one species can change the food environment and impact others.

Examples:

A microbe might lower the pH (make the environment more acidic), inhibiting or encouraging other microbes’ growth.

It might reduce water activity or produce antimicrobial compounds

23
Q

what is chemical spoilage

Study These Flashcards
A

When chemical reactions spoil food by:
. light
. metal ions
. excessive heat

24
Q

What are 4 common signs of chemical spoilage

Study These Flashcards
A

Increased viscosity – food becomes thicker or stickier

Gelation – the liquid parts of the food form a gel

Sedimentation – particles settle out of a solution

Colour changes – browning, fading, or discolouration

25
what is lipid oxidation
When unsaturated C=C fatty acids react with oxygen, causing rancidity (lipolysis). . caused by lipoxygenase and photosensitisers
26
What do plants, roots, meats and fruits contain to stop lipid oxidation?
. antioxidants; . ascorbic acid . vitamin E (tocopherols) . carotenoids . flavonoids
27
How do antioxidants stop lipid oxidation?
Antioxidants inhibit lipid oxidation by acting as hydrogen or electron donors.
28
Describe enzymic browning in fruits
. the phenolic compounds, PPO ( both in fruits) are exposed to oxygen; they make quinones. . quinones advance into melanin, which causes browning. . Peroxidases can contribute to more browning, but it is not essential.
29
Describe in detail enzymic browning. Consider what is in fruits, what the fruit reacts with, what the product is that further reacts to form what pigment and what can contribute.
Phenolic compounds and polyphenol oxidase (PPO) are both present inside fruit cells. When the fruit is damaged or cut, oxygen enters and mixes with the PPO and phenolic compounds. PPO catalyzes the oxidation of phenolic compounds into quinones. Quinones are highly reactive and undergo further reactions to form melanin-like polymers, which appear as brown pigments — this is enzymatic browning. Peroxidases can contribute to browning by oxidizing phenolics as well, but PPO is the primary enzyme involved and essential for enzymatic browning. Peroxidase plays a supporting role, not a central one.
30
How does sodium sulfite affect enzymic browning
It removes oxygen from water, which slows browning
31
how does copper sulfate affect the enzymic reaction
It is an essential cofactor in the enzymic reaction. Increase the rate of browning.
32
How does thiourea affect the rate of enzymic reaction?
Thiourea is an inhibitor of polyphenoloxidase, it slows the enzymic reaction
33
How does ascorbic acid affect enzymic browning
It lowers the pH, enzymes are not working optimally, and slows the reaction.
34
Describe non-enzymic browning
When reducing sugars react with amino acids when heated over 120 degrees. This forms melanoidins.
35
Describe how meat changes colour when spoilt.
1. The colour of meat comes from myoglobin protein, which holds oxygen. 2. When meat is cut and exposed to air, oxygen binds to myoglobin → forms oxymyoglobin → gives a bright red colour (like fresh beef). 3. Over time, or with low oxygen, myoglobin turns into metmyoglobin, which is brown, seen in older or spoiled meat.
36
describe how fish change colour when spoilt
When fish starts to spoil, the flesh can turn yellow. This happens because of oxidation: Carotenoids (natural pigments in fish) break down when they react with oxygen. Lipids (fats) in the fish also oxidise, forming yellow or brownish compounds. This non-enzymic process happens without enzymes, just from exposure to air, light, and time.
37
what is shelf life
Shelf life refers to the time a food remains safe to consume and maintains its desired quality (such as taste, texture, appearance, and nutritional value) under specific storage conditions.
38
what is shelf life
Shelf life is how long a food can stay safe and high quality under certain storage conditions. It starts from the date of manufacture.
39
when does shelf life begin
Shelf life begins immediately after the product is manufactured
40
why is shelf life important
✅ Consumer safety: To ensure the product does not pose a health risk during its shelf life. ✅ Regulatory compliance: Food safety authorities require that manufacturers provide clear expiration information. ✅ Product recalls prevention: If products spoil earlier than expected, it can lead to costly recalls, damage to brand reputation, and legal consequences. ✅ Quality assurance: Maintaining product texture, flavour, colour, and nutritional value for as long as possible. ✅ Optimised logistics and distribution: Knowing the shelf life allows for better supply chain management and reduced waste
41
state ways to microbiologically test shelf life
.* Food-borne microorganisms: (e.g. Listeria, Salmonella, Campylobacter, E. coli, Yeasts and Moulds, Staphylococcus aureus, Bacillus cereus, Lactic Acid Bacteria) * Total viable count * Enterobacteriaceae . Calculating Total Viable Count (TVC): A general measure of microbial population in the food. . Calculating Enterobacteriaceae count: Indicates faecal contamination or poor hygiene
42
What can shelf life be affected by, State 4 things
1. How the food is made (manufacturing process) 2. The packaging used 3. its storage (temperature, humidity, etc.) 4. The ingredients in the product
43
Why is shelf life important
1. Consumer safety 2. Good quality 3. Fewer product recalls 4. Better product development and profitability
44
what are the two types of shelf life indication
1. Best before date: the length of time a food can reasonably be expected to retain its best quality, e.g. flavour, texture, taste. Normally, for non-perishable foods: canned, dried, frozen. 2. Use by date: When stored under stated storage conditions, a food is expected to be safe to consume. . Food poisoning is risky if the use-by date is not adhered to. For chilled dairy products, cooked meats and prepared salads.
45
state three microbiological tests
Pathogen detection: Tests for harmful bacteria like Salmonella, Listeria monocytogenes, E. coli, Staphylococcus aureus, etc. Total Viable Count (TVC): A general measure of microbial population in the food. Enterobacteriaceae count: Indicates faecal contamination or poor hygiene.
46
state physical/chemical test of shelf life
* Water activity * Moisture content * pH
47
What is water activity
Water activity (aw) refers to the amount of free water available in food for microbial growth. A value of 1.0 represents pure water, while 0.0 represents a completely dry substance
48
what is moisture content
Moisture content is the total amount of water present in a food sample. Expressed as a percentage of the food's total weight.

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