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MICR3215: Food Microbiology and Biotechnology > Food Spoilage > Flashcards

Food Spoilage Flashcards

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1
Q

When is food considered spoiled?

A

When there is an undesirable change in the colour, flavour, odour or texture if the food has occurred.

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2
Q

What are the factors that lead to spoiling occurring?

A
  1. Poor Sanitation
  2. Enzymatic or chemical reactions
  3. Improper temperature controls
  4. Microbial growth
  5. Physical abuse
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3
Q

Name the two types of spoilage and discuss their causes.

A
  1. Microbial spoilage - caused growth of the microorganisms, action of microbial enzymes or microbial products.
  2. non-microbial spoilage - caused by foreign material in the foodstuff or by enzymes that occur in the foodstuff naturally
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4
Q

What are the quality parameters used to detect spoilage in foods (by microbes) and how are they showcased in food?

A
  1. General Appearance: Mould growth, slime formation, production of gas (pockets of gas, bubbles)
  2. Colour: Discolouration (often pink, grey, red or green)
  3. Texture: Loss of texture (Soft, Mushy)
  4. Odour: Decomposition odours (putrid, sulphur, sweet, alcoholic)
  5. Flavour: “Off flavours” (Bitter, Yeasty, Rancid)
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5
Q

What are the events that must take place for microbial spoilage to take?

A

For microbial food spoilage to occur, several events must take place in sequence:
1. the food must provide suitable food for the contaminating microorganisms
2. the food environment should favour growth of the microorganisms (pH, Aw, redox potential, nutrients, growth factors, etc)
3. the food must be stored at a temperature that enables the microbes to multiply
4. the food must be stored at the conditions of growth long enough for microbes to multiply and get to high enough numbers to result in detectable changes

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6
Q

Under the conditions of storage, how is bacterial load increased?

A

Microbes with the shortest generation time will increase in numbers rapidly and result in spoilage.

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7
Q

Define “spoilage detection level”.

A

The level of microbes necessary to cause spoilage. This level varies.

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8
Q

What are the different groups of foods based on their susceptibility to spoilage?

A
  • Perishable: spoils quickly (days)
  • Semi- perishable: relatively long shelf life (weeks to months)
  • Non-perishable: very long shelf life (months - years)
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9
Q

What are some examples of the different food types?

A
  1. Perishable: meats, fish, poultry, eggs, milk, most fruits and vegetables
  2. Semiperishable: Potatoes, apples, nuts
  3. Non perishable: sugar, flour, rice and dry beans
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10
Q

Name the bacterial species have been proven to be involved in the spoilage of most foods.

A

Three categories:
1. Psychrotrophic
2. Thermophilic
3. Aciduric

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11
Q

Discuss the Psychrotrophic organisms.

A
  • Growth range 5 C and below
  • May multiply rapidly at 10 - 25 C
  • Causes spoilage in foods stored at low temperatures
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12
Q

What type of food spoilage microorganisms are typically psychrotrophic?

A

Yeasts and Moulds

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13
Q

Discuss Thermophilic organisms.

A
  • Growth range 40 - 90 C
  • Optimum range 55 - 65 C
  • Thermoduric vegetative bacterial cells surviving low heat treatment (pasteurization) or those getting in food as post heat contamination also multiply in these warm foods
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14
Q

What are some typical examples of thermophilic organisms?

A
  • Pediococcus acidilatici
  • Streptococcus thermophilus
  • Bacillus sp
  • Clostridium sp
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15
Q

Discuss aciduric organisms.

A
  • These bacteria capable of growing rapidly at pH 4.6 or below
  • Associated with spoilage of acidic food products such as fruit juices, pickles, salsa, salad dressing, mayonnaise and fermented sausages
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16
Q

What are some organisms that are aciduric?

A
  • Yeasts and moulds
  • Lactic acid bacteria (such as Lactobacillus fructivorans, L. Fermentum, Pediococcus acidilatici
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17
Q

How are spoilage microorganisms introduced in vegetables?

A
  • Microorganisms from soil, water and air (may include plant pathogens)
  • Microbes grow rapidly on damaged or cut vegetables
  • Spoilage increases in the presence of air, high humidity and storage
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18
Q

In vegetables, what are the microorganisms commonly associated with spoilage?

A
  • Moulds: Penicillium, Aspergillus
  • Bacteria: Pseudomonas, Erwinia, Bacillus, Clostridium
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19
Q

What is vegetable spoilage referred to and what are some types?

A
  • Referred to as ROT
  • Examples: Black rot, Grey rot, Pink rot, Soft rot, Stem Rot
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20
Q

When vegetables are spoiling, what are the changes seen?

A
  • Colour changes
  • Loss of texture
  • Off odour
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21
Q

List the spoilage microorganisms that cause spoilage in fruits.

A
  1. Moulds - Penicillium, Aspergillus, Rhizopus
  2. Yeasts - Saccharomyces
  3. Aciduric bacteria -Lactic acid bacteria, Acetobacter, Gluconobacter
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22
Q

What is spoilage in fruits referred to as?

A

Rot

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23
Q

What are the effects of spoilage microorganisms on fruits?

A
  • Yeast cause fermentation of fruits such as apple, strawberries, citrus fruits
  • Souring of berries is caused by bacterial spoilage due to lactic acid and acetic acid
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24
Q

What characteristic of grains normally inhibits microbial growth?

A
  • Grains and seeds normally have 10-12% moisture which lowers the water activity to less than or equal to 0.6
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25
Q

What and how does spoilage occur in grains?

A
  • Spoilage in grains is attributed to mould growth
  • Mould growth occurs when water activity increases above 0.6
  • This normally happens in cereals during harvesting, processing and storage
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26
Q

In red meats, what is the microbiota reflective of?

A

The biota is generlly reflective of the slaughtering and processing environments

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27
Q

What are the types and examples of microorganisms dominating red meats?

A
  1. Gram neg: Acinetobacter, Escherichia, Pseudomonas
  2. Gram Positive: Enterococcus, Lactobacillus
  3. Yeast & Mould: Penicillium, Mucor, Candida
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28
Q

What are the primary sources of microorganisms in meats?

A
  1. Stick knife
  2. Animal hide
  3. Gastrointestinal tract
  4. Hands of handlers
  5. Containers
  6. Handling and storage environment
  7. Lymph nodes
29
Q

In red meats, what factors determine the predominant spoilage microbe?

A
  • Nutrient availability
  • Oxygen availabilty
  • Storage temperature
  • pH
  • Generation time of microbes
30
Q

In the storage of red meats at refrigerated temps (less than 5 degrees C), what is the predominant spoilage organisms and how does it cause spoilage?

A
  • Spoilage organism: psychotrophic bacteria such as Clostridium
  • These organisms (Clostridium) causes proteolysis resulting in liquid in the bag and a offensive odour.
31
Q

In the storage of red meats at anaerobic/low temps, what is the predominant spoilage organisms and how does it cause spoilage?

A

-Spoilage organisms: Facultative anaerobes such as Pseudomonas sp
- Facultative anaerobes, like Enterobacter, metabolise amino acids to form amines and ammonia to cause purifications

32
Q

In the storage of red meats at anaerobic conditions (vacuum) packed meats, what is the predominant spoilage organisms and how does it cause spoilage?

A
  • Spoilage organisms: facultative anaerobes such as Lactobacillus sp
  • Causes a cheesy odour due to the production of lactic acid.
    Hydrogen sulphide may also be produced causing odour and colour change (H2S oxidizes myoglobinto a green colour)
33
Q

In the storage of red meats at low pH and/or low glucose content, what is the predominant spoilage organisms and how does it cause spoilage?

A
  • Spoilage organisms: Acinetobacter & Moraxella
  • Produces undesirable odours and slime.
  • The colour of the meat usually becomes grey or brown due to the oxidation of myglobin
34
Q

Why does ground meats spoil more rapidly than other meats?

A

The meat has more surface area

35
Q

The category “Ready-to-eat Meats” includes:

A
  1. High heat processed meats
  2. Low Heat Processed Meats
  3. Uncured Meats
36
Q

Define commercially sterile.

A

The destruction of all pathogenic and and spoilage organisms that can grow in food under normal storage and handling conditions.

37
Q

In Ready to Eat Meats Products, how are microorganisms introduced?

A
  • Can enter as post-heat treatment, contaminants from equipment, personnel or air
38
Q

What are some examples of the microorganisms that contaminate “Ready to Eat Meats” what’s the result of said contamination?

A
  • Example of microorganisms: Lactobacillus and Leuconostoc
  • These organisms contaminate vacuum packed roast beef, chicken and turkey.
  • The result is gas production and liquid production.
  • cloudy appearance, large accumulation of gas, liquid and slime
39
Q

Fill in the blanks: There are over __ genera of bacteria which may be found in fresh poultry.

A

25

40
Q

Low temperature spoilage in poultry is due to what organisms?

A

-Primary organism: Pseudomonas
-Other organisms: Acinetobacter, Flavobacterium and Corynebacterium

41
Q

What are the features associated with spoilage in poultry?

A
  • Sliminess at the outer surfaces of the carcases or cut
  • Visceral cavity displays a sour odour (called visceral taint)
42
Q

Why is spoilage in poultry restricted to outer surfaces and cut portions?

A
  1. Inner portions of the poultry tissue are generally sterile or have very few organisms
  2. Spoilage bacteria are deposited on the surface from water, processing and handling
  3. The surface of fresh poultry stored in high humidity is susceptible to growth of aerobic bacteria like Pseudomonas
  4. Poultry skin supported spoilage bacteria better than the muscle tissue
43
Q

In advanced stages of poultry spoilage, what can be noticed?

A

The surfaces will fluoresce when exposed to UV light due to the presence of pigments produced by Pseudomonads.

44
Q

How are eggs contaminated?

A
  • shell of eggs are contaminated
  • the shells are contaminated with microbes from:
    1. Faecal matter
    2. Nesting material
    3. Feed, Air and Equipment
45
Q

What is a character of shelled eggs that increases the probability of spoilage and why?

A

Character: pores in the eggshells & inner membrane
Why: They do not prevent the entrance of bacteria and moulds from entering

46
Q

What intinsic/extrinsic factor can enhance the entrance of bacteria into the egg?

A
  • Moisture/Water Activity
47
Q

What microorganisms are commonly associated with spoilage of shelled eggs

A
  • Pseudomonas
  • Proteus
  • Aeromonas
  • coliform group
48
Q

Eggs have quite a few factors that inhibit microbial growth. Name some.

A
  1. Lysozyme
  2. Protease inhibitors
49
Q

What is spoilage in eggs known as?

A

Rot

50
Q

What are the different types of rot in eggs and how are they different?

A
  1. Green rot: greening of the albumin due to Pseudomonas fluorescens
  2. Black Rot: Muddy discoloration of the yolk due to hydrogen sulphide production by Proteus
  3. Red Rot: red colouration due to pigment produced by Serratia marsecens
  4. Fungal rot: due to the growth of Penicillium and Mucor inside eggs
51
Q

What are some examples of egg products and how is microbial growth prevented?

A
  • liquid eggs such as whole eggs , yolks and whites
  • they are often pasteurized and frozen to prevent microbial growth
52
Q

What type of microorganisms can grow and cause spoilage on egg products?

A
  • gram negative bacteria
  • psychrotrophic bacteria
53
Q

(T/F) - Dried eggs are not as susceptible to spoilage because of the low water activity.

A

True

54
Q

Discuss spoilage in fish.

A
  • Both freshwater and salt-water fish are susceptible to spoilage due to:
    1. autolytic enzymes
    2. oxidation of fatty acids
    3. microbial growth
  • If the fish is not gutted after it is caught, protein hydrolysis is the predominant form of spoilage
  • In fatty fish, spoilage occurs due to the oxidation of unsaturated fatty acids
55
Q

What are the factors that influence microbial spoilage in fish?

A

1.The type of microbes present and their levels
2.The environment of the fish
3. The type of fish
4. Methods used for harvest
5. Handling of the fish after catching

56
Q

List the major spoilage bacteria of fish.

A
  • Gram negative aerobic rods such as: 1. Pseudomonas sp
    2. Moraxella
    3. Flavobacterium
  • Facultative anaerobes such as: 1. Vibrio and 2. coliforms
57
Q

What effects do these spoilage microorganisms have on fish?

A
  • Pseudomonas: predominates under aerobic conditions both at refrigerated and slightly higher temperatures
  • Gram negative rods cause spoilage by first causing decay followed by purification which produce many volatile compounds and volatile fatty acids. This results in a stale/fishy/putrid odour
  • Slime is also produced and the gills and eyes are discoloured and the muscle texture lost
58
Q

What causes spoilage in the following:
1. Salted fish
2. Smoked fish
3. Canned fish

A
  1. Salted fish is susceptible to spoilage by halophiles (Vibrio & Micrococcus)
  2. Smoked fish - has low water activity but moulds may grow on the surface
  3. Canned fish- heat treated to produce commercially sterile products but thermophilic spore formers can spoil them and several gram-negative rods
59
Q

Why is microbial spoilage of shrimp more common than crabs and lobsters?

A

Because crabs and lobsters are kept alive until required but shrimp die during harvesting

60
Q

What is the predominant microflora that causes spoilage in crustaceans?

A
  • Pseudomonas
  • Several gram negative rods
61
Q

Describe spoilage in crustaceans.

A
  • Spoilage can be similar to that of fresh fish if the conditions are right
  • Spoilage of shrimp is noted by odour changes because of the production of volatile metabolites from decay and putrification
  • Slime production and texture and colour changes
62
Q

Describe spoilage in mollusks.

A
  • Since these (oysters, clams and scallops) are kept alive until needed, microbial spoilage occurs after processing
63
Q

What is the main spoilage organism for mollusks?

A
  • Pseudomonas
  • Gram negative rods
64
Q

Where do spoilage microorganisms come from in raw milk

A
  • Inside the udder
  • animal body surfaces
    *feed
  • air
  • water
  • utensils and equipment
65
Q

How does spoilage in raw milk occur?

A
  • occurs from the metabolism of lactose, protein compounds and fatty acids
66
Q

How does spoilage occur in raw milk under these conditions:
a) refrigerated
b) not refrigerated

A

a) Spoilage occurs from psychrotrophs such as Pseudomonas, Flavobacterium sp,Alcaligenes and coliforms

b) Mesophiles predominates for example, Lactobacillus, Lactococcus, Enterococcus, Clostridium and coliforms
- Lactose hydrolysing bacteria like Lactococcus cause curdling and souring of the milk.

67
Q

What causes spoilage in Pasteurized milk?

A
  • Thermoduric bacteria that survive pasteurization for example, Micrococcus, Enterococcus, Lactobacillus, Streptococcus etc
  • Post pasteurization contaminants such as coliforms, Pseudomonas, Flavobacterium
68
Q

How is spoilage prevented in Concentrated Liquid Products?

A

Sufficient heat treatment to kill vegetative cells and spores of moulds and some bacteria.

69
Q

Discuss spoilage in butter.

A
  • Bacteria like Pseudomonas and yeasts such as Candida and mould such as Geotrichum grow on the surface and cause flavour defects and discolouration
  • unsalted butter is susceptible to contamination of Enterococcus and Pseudomonas which grow causing flavour defects

MICR3215: Food Microbiology and Biotechnology (10 decks)

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