Meat spoilage Flashcards
Routine ante mortem inspection on farm in UK is legally permitted for..?
All species
Three phases following head-only electrical stunning
Tonic
Clonic
Recovery
pH change in 24hrs post death
7 to 5.5
Pre-rigor stage
meat soft pliable, ATP more or less constant myosin dissociates from actin, water holding capacity high
Rigor mortis
stiff meat, demonstrated by fall in ATP, actomyosin complex formed, water holding capacity minimum due to the drop of pH
Post rigor stage
complex biochemical changes breaking down muscle proteins leading to organoleptic changes and tender meat
Chemical aspects of meat spoilage
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)
Macroscopic signs of bacterial spoilage
§ Slime layer
§ Abnormal colour
§ Offensive odour
§ Abnormal texture
§ Occur on the surface and/or internally
Signs of spoilage by moulds and yeasts
○ 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
Temperature requirements for chilled raw meat
Red meat < +7 degrees
White meat < +4 degrees
Offal < +3 degrees
Pseudomonas spp in aerobic meat storage
○ Obligate aerobe, gram -ve rod
○ Especially at T<5 degrees
○ Generates a lower pH
○ Especially beef
Brochothrix thermosphaticum in aerobic meat spoilage
○ Facultative anaerobe, gram +ve rod
○ Dominant at T>5 degrees
○ Pork and lamb
○ pH5-9
Modified atmosphere packing of beef
80% O2, 20% CO2
What is the min temperature yeasts and moulds can grow?
-12 degrees
Spoilage is primarily due to…
oxidation of fats
Pasteurisation
<100 degrees, low temp, long time or high temp short time
Sterilisation
> 100 degrees, e.g. UHT milk
Canning food
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)
Preservation with anti-microbials
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
Vacuum packaging
CO2 rises to 20%, oxygen falls to 1%
