Meat spoilage

Question 1

Routine ante mortem inspection on farm in UK is legally permitted for..?

Answer 1

All species

Question 2

Three phases following head-only electrical stunning

Answer 2

Tonic
Clonic
Recovery

Question 3

pH change in 24hrs post death

Answer 3

7 to 5.5

Question 4

Pre-rigor stage

Answer 4

meat soft pliable, ATP more or less constant myosin dissociates from actin, water holding capacity high

Question 5

Rigor mortis

Answer 5

stiff meat, demonstrated by fall in ATP, actomyosin complex formed, water holding capacity minimum due to the drop of pH

Question 6

Post rigor stage

Answer 6

complex biochemical changes breaking down muscle proteins leading to organoleptic changes and tender meat

Question 7

Chemical aspects of meat spoilage

Answer 7

Proteins degrade to amino acids
§ No negative sensory quality
§ Free amino acids degrade to ammonia, H2S (hydrogen sulfide/hydrosulfuric acid), amines… (putreficative spoilage)
§ Myoglobin becomes grey/green on oxidation

Carbohydrates oxidize to acids (souring)

Fats oxidize to aldehydes and ketones (rancidity)

Question 8

Macroscopic signs of bacterial spoilage

Answer 8

§ Slime layer
§ Abnormal colour
§ Offensive odour
§ Abnormal texture
§ Occur on the surface and/or internally

Question 9

Signs of spoilage by moulds and yeasts

Answer 9

○ Stickiness
○ Mycelia
○ Musty flavour (meat) and/or rancidity (fat)
○ Can grow on frozen meats (where temp is >-10 degrees)
○ Coloured spots
§ Penicillin: white or pale green
§ Mucor whiskers
§ Cladosporium: black spots
§ Sporotrichum: white spot
§ Yeasts
§ Rhodotorula: pink colonies

Question 10

Temperature requirements for chilled raw meat

Answer 10

Red meat < +7 degrees
White meat < +4 degrees
Offal < +3 degrees

Question 11

Pseudomonas spp in aerobic meat storage

Answer 11

○ Obligate aerobe, gram -ve rod
○ Especially at T<5 degrees
○ Generates a lower pH
○ Especially beef

Question 12

Brochothrix thermosphaticum in aerobic meat spoilage

Answer 12

○ Facultative anaerobe, gram +ve rod
○ Dominant at T>5 degrees
○ Pork and lamb
○ pH5-9

Question 13

Modified atmosphere packing of beef

Answer 13

80% O2, 20% CO2

Question 14

What is the min temperature yeasts and moulds can grow?

Answer 14

-12 degrees

Question 15

Spoilage is primarily due to…

Answer 15

oxidation of fats

Question 16

Pasteurisation

Answer 16

<100 degrees, low temp, long time or high temp short time

Question 17

Sterilisation

Answer 17

> 100 degrees, e.g. UHT milk

Question 18

Canning food

Answer 18

Cans filled under steam and then sealed creating a vacuum

Followed by heating at 115 degrees under pressure, 23-100 mins

Different foods cooked at different temperatures and durations (meats lower and longer, liquids shorter and hotter)

Question 19

Preservation with anti-microbials

Answer 19

Nisin added to cheese
○ From lactic acid bacteria
○ Effective against gram +ve and spore formers

Nitrates/nitrites added to cured meats, inhibits bacteria

Smoking fish and meat, released antibacterial phenolics

Question 20

Vacuum packaging

Answer 20

CO2 rises to 20%, oxygen falls to 1%