L23: Meat Spoilage

Question 1

Which kind of microbes predominate at spoilage?

Answer 1

A few kinds of bacteria

Question 2

What mechanism produces lactic acid in the dead animal?

Answer 2

Anaerobic glycolysis

Question 3

What is the pH drop in the first 24 hours?

Answer 3

7 to 5.5

Question 4

Is a low or high pH better?

Answer 4

Low

Question 5

How can you speed up a low pH?

Answer 5

Electrical stimulation

Question 6

In which animals is rigor mortis very fast?

Answer 6

Stressed

Question 7

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

Answer 7

Amino acids, doesn’t

Question 8

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

Answer 8

NH3, H2S, amines - putrefaction

Question 9

What happens to myoglobin on oxidation?

Answer 9

Becomes green/grey

Question 10

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

Answer 10

Acids - souring

Question 11

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

Answer 11

Aldehydes and ketones - rancidity

Question 12

What are 4 macroscopic signs of bacterial spoilage?

Answer 12

Slime layer, abnormal colour, offensive odour, abnormal texture

Question 13

What are 4 signs of spoilage by yeast and mould?

Answer 13

Stickiness, visible fungal threads, musty flavour, rancidity

Question 14

What microbe can still grow on frozen meats?

Answer 14

Fungi

Question 15

What does penicillin look like?

Answer 15

White

Question 16

What does mucor look like?

Answer 16

Whiskers

Question 17

What does cladosporum look like?

Answer 17

Black spots

Question 18

What does sporotrichum look like?

Answer 18

White spots

Question 19

What does rhodotorula look like?

Answer 19

Pink

Question 20

Which meat does Pseudomonas especially grow on?

Answer 20

Beef

Question 21

Which temperature does Pseudomonas especially grow at?

Answer 21

Less than 5

Question 22

How does Pseudomonas affect pH?

Answer 22

Generates a lower pH

Question 23

What are characteristics of Pseudomonas?

Answer 23

Obligate anaerobe, gram -ve rod

Question 24

Which meats are especially susceptible to Brocothrix?

Answer 24

Pork and lamb

Question 25

Above which temperatures is Brocothrix dominant?

Answer 25

Over 5

Question 26

Which pH is brocothrix?

Answer 26

5-9

Question 27

What are characteristics of Brocothrix?

Answer 27

Facultative anaerobe, gram +ve rod

Question 28

Above what cfu/g do you see slime?

Answer 28

10^8

Question 29

Above what cfu/g do you get malodour?

Answer 29

10^7

Question 30

What is redox potential like in minced meat?

Answer 30

High

Question 31

What are three examples of bacteria colonising minced meat?

Answer 31

Pseudomonas, Enterobacteriacea, Brocothrix

Question 32

Which kind of bacteria grow on low pH meat?

Answer 32

Lactate fermenters

Question 33

Which kind of pH meat does Brochothrix grow on?

Answer 33

High

Question 34

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

Answer 34

Leuconostoc, Carnobacterium

Question 35

What is in modified atmosphere packaging for beef?

Answer 35

80% O2, 20% CO2

Question 36

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

Answer 36

Nice and red but get aerobic putrefaction by Pseudomonas

Question 37

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

Answer 37

SLows down putrefaction but still permits spoilage due to lactate fermenters

Question 38

Which meat do eviscerated birds spoil similarly to?

Answer 38

Red

Question 39

Where are bacteria distributed in eviscerated birds?

Answer 39

Cut surfaces and feather holes

Question 40

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

Answer 40

Discolouration

Question 41

What is the problem with 100% CO2 packaging?

Answer 41

Still spoils due to lactate

Question 42

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

Answer 42

Dry integral skin

Question 43

How does spoilage start in uneviscerated birds?

Answer 43

Internally when H2S from gut diffuses into muscle

Question 44

What causes greenstrike in uneviscerated birds?

Answer 44

H2S, myoglobin, oxygen

Question 45

Which kind of meats show "bone taint"?

Answer 45

Cured meats

Question 46

Which tissues in bone taint associated with?

Answer 46

Deep meat or bone marrow

Question 47

What causes bone taint?

Answer 47

Putrefaction by psychotropic bacteria eg Clostridium

Question 48

Which manufacturing problems lead to bone taint?

Answer 48

Poor distribution of curing agents, contamination during sticking

Question 49

Which kind of weather is bone taint common in?

Answer 49

Warm

Question 50

Which kind of meat is bone taint common in?

Answer 50

High pH

Question 51

Why can bacteria not grow on frozen meat?

Answer 51

Enzyme activity requires liquid phase

Question 52

Below which temperature will mould and yeast not grow?

Answer 52

12 degrees

Question 53

What causes spoilage in frozen meat?

Answer 53

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

Question 54

Why do chilled vacuum packages of bacon spoil?

Answer 54

Mainly lactate fermenters, along with Brochothrix, Micrococcus

Question 55

What causes spoilage in warm cooked ham?

Answer 55

Spore formers e.g. Clostridia, Bacillus

Question 56

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

Answer 56

Lactate fermenters

Question 57

When can chilled cooked ham be recontaminated?

Answer 57

At handling

Question 58

What can chilled cooked ham be recontaminated with?

Answer 58

Pseudomonas, Brochothrix, lactate fermenters, staph, moulds

Question 59

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

Answer 59

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

Question 60

What is aw?

Answer 60

The available water, not the water content

Question 61

What factors of bacterial growth does the aw affect?

Answer 61

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

Question 62

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

Answer 62

Decrease aw

Question 63

What are three examples of antimicrobials intrinsic in food?

Answer 63

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

Question 64

What inhibits bacteria in cured meats?

Answer 64

Nitrates/nitrites

Question 65

What process releases antibacterial phenolics in fish and meat?

Answer 65

Smoking

Question 66

What produces nisin in cheese?

Answer 66

Lactic acid bacteria

Question 67

What is nisin in cheese effective against?

Answer 67

Gram +ves and spore formers

Question 68

How does relative humidity affect aw?

Answer 68

Causes food to absorb or lose water so changing their aw

Question 69

How does decreasing relative humidity during chilling inhibit microbial multiplication?

Answer 69

Dries the surface

Question 70

What are CO2 and O2 percentages in vacuum packing?

Answer 70

CO2 rises to 20% and O2 falls to 1%

Question 71

WHy is 100% CO2 packing only done in poultry?

Answer 71

Discolours myoglobin

Question 72

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

Answer 72

Oxygen in red meat, nitrogen in poultry

Question 73

How does low temperature affect antimicrobial action of CO2?

Answer 73

Enhances

Question 74

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

Answer 74

Gram -ves more than gram +ves

Question 75

Below what temperature is spoilage down to fat oxidation?

Answer 75

-10

Question 76

Why do microbes survive in slow freezing??

Answer 76

External water freezes before cell contents

Question 77

Why does rapid freezing result in death?

Answer 77

Water in bugs crystallises

Question 78

Below what temperature is pasteurisation?

Answer 78

100

Question 79

At what temp and for how long is pasteurisation?

Answer 79

72 degrees for 15 seconds

Question 80

Above what temperature is sterilisation?

Answer 80

100

Question 81

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

Answer 81

115 degrees for 23-100 minutes

Question 82

What is sterilisation like for meats?

Answer 82

Lower and longer

Question 83

What is sterilisation like for liquids?

Answer 83

Shorter and hotter

Question 84

What can non-ionising radiation be used to disinfect?

Answer 84

Surfaces only

Question 85

Why which mechanism does UV irradiation work?

Answer 85

Directly bacteriostatic plus ozone

Question 86

What is used to generate gamma rays?

Answer 86

cobalt 60

Question 87

What does gamma irradiation require and what does this become?

Answer 87

Water - becomes peroxides and oxides

Question 88

Which products can you use gamma irradiation on?

Answer 88

Chilled or frozen

Question 89

What is a disadvantage of gamma irradiation?

Answer 89

May change nutrients

Question 90

Which food is gamma irradiated licensed for?

Answer 90

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

Question 91

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

Answer 91

Spores

Question 92

Which genes could be exploited in bacteria?

Answer 92

Heat shock

Question 93

Which microorganisms are most and least resistant to heat?

Answer 93

Spores most, viruses least

Question 94

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

Answer 94

Viruses most, gram -ves least