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VPH > L23: Meat Spoilage > Flashcards

L23: Meat Spoilage Flashcards

1
Q

Which kind of microbes predominate at spoilage?

A

A few kinds of bacteria

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2
Q

What mechanism produces lactic acid in the dead animal?

A

Anaerobic glycolysis

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3
Q

What is the pH drop in the first 24 hours?

A

7 to 5.5

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4
Q

Is a low or high pH better?

A

Low

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5
Q

How can you speed up a low pH?

A

Electrical stimulation

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6
Q

In which animals is rigor mortis very fast?

A

Stressed

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7
Q

What do proteins degrade to and how does this affect sensory quality?

A

Amino acids, doesn’t

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8
Q

What do free amino acids degrade to an how does this affect sensory quality?

A

NH3, H2S, amines - putrefaction

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9
Q

What happens to myoglobin on oxidation?

A

Becomes green/grey

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10
Q

What do carbohydrates oxidise to and what is this process called?

A

Acids - souring

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11
Q

What do fats oxidise to and what is this process called?

A

Aldehydes and ketones - rancidity

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12
Q

What are 4 macroscopic signs of bacterial spoilage?

A

Slime layer, abnormal colour, offensive odour, abnormal texture

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13
Q

What are 4 signs of spoilage by yeast and mould?

A

Stickiness, visible fungal threads, musty flavour, rancidity

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14
Q

What microbe can still grow on frozen meats?

A

Fungi

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15
Q

What does penicillin look like?

A

White

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16
Q

What does mucor look like?

A

Whiskers

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17
Q

What does cladosporum look like?

A

Black spots

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18
Q

What does sporotrichum look like?

A

White spots

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19
Q

What does rhodotorula look like?

A

Pink

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20
Q

Which meat does Pseudomonas especially grow on?

A

Beef

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21
Q

Which temperature does Pseudomonas especially grow at?

A

Less than 5

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22
Q

How does Pseudomonas affect pH?

A

Generates a lower pH

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23
Q

What are characteristics of Pseudomonas?

A

Obligate anaerobe, gram -ve rod

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24
Q

Which meats are especially susceptible to Brocothrix?

A

Pork and lamb

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25
Q

Above which temperatures is Brocothrix dominant?

A

Over 5

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26
Q

Which pH is brocothrix?

A

5-9

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27
Q

What are characteristics of Brocothrix?

A

Facultative anaerobe, gram +ve rod

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28
Q

Above what cfu/g do you see slime?

A

10^8

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29
Q

Above what cfu/g do you get malodour?

A

10^7

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30
Q

What is redox potential like in minced meat?

A

High

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31
Q

What are three examples of bacteria colonising minced meat?

A

Pseudomonas, Enterobacteriacea, Brocothrix

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32
Q

Which kind of bacteria grow on low pH meat?

A

Lactate fermenters

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33
Q

Which kind of pH meat does Brochothrix grow on?

A

High

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34
Q

What are two examples of lactate fermenters giving a cheesy odour?

A

Leuconostoc, Carnobacterium

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35
Q

What is in modified atmosphere packaging for beef?

A

80% O2, 20% CO2

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36
Q

What is an advantage and disadvantage of high oxygen in MAP beef?

A

Nice and red but get aerobic putrefaction by Pseudomonas

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37
Q

What is an advantage and disadvantage of adding CO2 in MAP beef?

A

SLows down putrefaction but still permits spoilage due to lactate fermenters

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38
Q

Which meat do eviscerated birds spoil similarly to?

39
Q

Where are bacteria distributed in eviscerated birds?

A

Cut surfaces and feather holes

40
Q

Why is vacuum/anaerobic packaging not used in eviscerated birds?

A

Discolouration

41
Q

What is the problem with 100% CO2 packaging?

A

Still spoils due to lactate

42
Q

Why do un-eviscerated birds have a longer storage life?

A

Dry integral skin

43
Q

How does spoilage start in uneviscerated birds?

A

Internally when H2S from gut diffuses into muscle

44
Q

What causes greenstrike in uneviscerated birds?

A

H2S, myoglobin, oxygen

45
Q

Which kind of meats show “bone taint”?

A

Cured meats

46
Q

Which tissues in bone taint associated with?

A

Deep meat or bone marrow

47
Q

What causes bone taint?

A

Putrefaction by psychotropic bacteria eg Clostridium

48
Q

Which manufacturing problems lead to bone taint?

A

Poor distribution of curing agents, contamination during sticking

49
Q

Which kind of weather is bone taint common in?

50
Q

Which kind of meat is bone taint common in?

51
Q

Why can bacteria not grow on frozen meat?

A

Enzyme activity requires liquid phase

52
Q

Below which temperature will mould and yeast not grow?

A

12 degrees

53
Q

What causes spoilage in frozen meat?

A

Oxidation of fats (less unsaturated fatty acids, longer shelf life)

54
Q

Why do chilled vacuum packages of bacon spoil?

A

Mainly lactate fermenters, along with Brochothrix, Micrococcus

55
Q

What causes spoilage in warm cooked ham?

A

Spore formers e.g. Clostridia, Bacillus

56
Q

What does chilled, cooked, vacuum packed ham spoil due to?

A

Lactate fermenters

57
Q

When can chilled cooked ham be recontaminated?

A

At handling

58
Q

What can chilled cooked ham be recontaminated with?

A

Pseudomonas, Brochothrix, lactate fermenters, staph, moulds

59
Q

What are 4 factors affecting the redox potential of a food?

A

The chemical nature of the product, the pH, the availability of oxygen, microbial activity

60
Q

What is aw?

A

The available water, not the water content

61
Q

What factors of bacterial growth does the aw affect?

A

Lag phase, log phase, maximum cell yield, spore germination

62
Q

How do salt, sugar, freezing, drying all work?

A

Decrease aw

63
Q

What are three examples of antimicrobials intrinsic in food?

A

Lysozyme in egg whites, lactoperoxidase system in milk, low MW components like herbs and spices

64
Q

What inhibits bacteria in cured meats?

A

Nitrates/nitrites

65
Q

What process releases antibacterial phenolics in fish and meat?

66
Q

What produces nisin in cheese?

A

Lactic acid bacteria

67
Q

What is nisin in cheese effective against?

A

Gram +ves and spore formers

68
Q

How does relative humidity affect aw?

A

Causes food to absorb or lose water so changing their aw

69
Q

How does decreasing relative humidity during chilling inhibit microbial multiplication?

A

Dries the surface

70
Q

What are CO2 and O2 percentages in vacuum packing?

A

CO2 rises to 20% and O2 falls to 1%

71
Q

WHy is 100% CO2 packing only done in poultry?

A

Discolours myoglobin

72
Q

Which gas is used along with raised CO2 in MAP in red meat and poultry?

A

Oxygen in red meat, nitrogen in poultry

73
Q

How does low temperature affect antimicrobial action of CO2?

74
Q

Which kind of bacteria are more sensitive to antimicrobial action of CO2?

A

Gram -ves more than gram +ves

75
Q

Below what temperature is spoilage down to fat oxidation?

76
Q

Why do microbes survive in slow freezing??

A

External water freezes before cell contents

77
Q

Why does rapid freezing result in death?

A

Water in bugs crystallises

78
Q

Below what temperature is pasteurisation?

79
Q

At what temp and for how long is pasteurisation?

A

72 degrees for 15 seconds

80
Q

Above what temperature is sterilisation?

81
Q

To what temperature and for how long is canned food heated?

A

115 degrees for 23-100 minutes

82
Q

What is sterilisation like for meats?

A

Lower and longer

83
Q

What is sterilisation like for liquids?

A

Shorter and hotter

84
Q

What can non-ionising radiation be used to disinfect?

A

Surfaces only

85
Q

Why which mechanism does UV irradiation work?

A

Directly bacteriostatic plus ozone

86
Q

What is used to generate gamma rays?

87
Q

What does gamma irradiation require and what does this become?

A

Water - becomes peroxides and oxides

88
Q

Which products can you use gamma irradiation on?

A

Chilled or frozen

89
Q

What is a disadvantage of gamma irradiation?

A

May change nutrients

90
Q

Which food is gamma irradiated licensed for?

A

Herbs/spices, fruit/veg, cereals, poultry, seafood

91
Q

For which microorganisms will high pressure/voltage technques not work?

92
Q

Which genes could be exploited in bacteria?

A

Heat shock

93
Q

Which microorganisms are most and least resistant to heat?

A

Spores most, viruses least

94
Q

Which microorganisms are most and least resistant to radiation and UV?

A

Viruses most, gram -ves least

VPH (32 decks)

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