Food Preservation and Processing Methods Flashcards
When does optimal palatability of meat develop?
2-3 weeks depending on species with chilling
What are the three main processes of meat palatability development?
Acidification, rigor mortis and conditioning
Describe the process of meat acidification?
How long does it take in Beef and pigs?
What is the normal pH of meat?
What causes PSE and DFD meat?
- In the presence of O2- glycogen breaks down to pyrucic acid then to CO2 and H20
- Without O2- glycogen breaks down to lactic acid
- pH drops in beef muscle 36-46 hous, Pigs 4-8 hours
- Protein denaturation, meat paler and more opaque- ability to bind to water decreases
- Normal pH between 5.6-6.2
PSE- pale soft exudative meat- accelerated anaerobic glycolysis: fast and excessive drop in pH to 5.2-5.4, poor water holding capacity, pale colour, soft texture- caused by stress at slaughter
DFD- dark firm and dry- not enough glycogen pH 6-6.2 dark, dry surface, high water holding capacity, shorter shelf life, poor consumer perception- caused by chronic stress
What causes Rigor Mortis?
Why do stress animals have more rapid rigor mortis?
Why is hip suspension used?
What does electrical stimulation achieve?
Rigor mortis is causes by the inavailability of ATP which can no longer be generated and fixes the length of sarcomeres and therefore muscle length and texture
Stressed animals use up glygocen due to cortisol, therefore have less ATP available and rigor mortis is more rapid
Hip suspension of carcasses during chilling- mechanically reduced shortening of the main muscles
Electrical stimulation-
main objective is to accelerate pH decline after death in order to implement a chilling ststem without risk of cold contraction
Ensure meat is tender under rapid carcass chilling
Accelerated normal PM changes- rigor morti sooner
What is cold shortening?
Muscles enter rigor mortis at 10-15 degrees for optimum tenderness
Very fast chilling of carcasses- especially lamb
What is conditioning?
What increases the rate?
What are the different reccomended times for meat?
Conditioning is the natural process which improved eating quality of beef- flavour and tenderness
Industry- carcasses or comercial cuts are held under refrigeration and controlled storage conditions
Conversion of muscle to meat- natural enzymes from muscle degrade specific proteins from muscle fibres
Rate of tenderisation increases with temperature
Different recommended times- poultry 1 days, pork 4-10 days, lamb 7-14 days, beef 10-21 days
Why is chilling used?
When should it start?
What are the regulations for chilling temperature?
Chilling- critical for meat hygiene, safety, product shelf-life, appearance and eating quality
Carcass chilling should start within 1h or exsanguinatino and occur so 4 degrees is reached in 24 hours
Regulations- carcass must be:
<7 degrees for red meat, <4 for white, <3 for offal
What are three types of dry chilling?
What is the differences?
Whist are most/least common?
Slow air refrigeration- used rarely in small abattoirs
three steps- carcass draining at ambient temp for few hours, prerefrigeration (10 d), refrigeration (4-7d)
Drying carcass surface- surface microbiota supressed, long time ambient temp (growth of bacteria), weight loss high
Rapid air refrigeration- most common
Carcassesa re exposed to air at 1 to -1 degrees for 18-36 hours, weight loss 1.5-2%
Ultra-rapid refrigeration- two phases
carcass exposed to intensive circulation of very cold air in special tunnels for 1-3h
Then refrigeration at -1 to 2 degrees for 18-22h/14-16 for cattle/pig
Weight loss only 1%
What is wet chilling used for?
What can it cause?
Poultry offal and poultry sold if frozen- spin chillers
Can cause cross contamination and water absorption
What is spray chilling?
What is the problem caused?
Spray- intermittent spraying of red meat carcasses with water
Problem- surface stays wet, better survival or microorganisms
What temperature are carcasses kept at on shelves?
What is the shelf-life of different meats?
Chilling shelf life- -1 to +2d
Shelf life-
beef carcasses 3-4 weeks, veal 3 weeks, lamb- 1-2 weeks, pig 10-14 days, offal 3 days
What main bacteria, mould and yeasts are responsible for food spoilage?
What are the chemical aspects of food spoilage?
Bacteria-
psudomonas, lactobacillus, brochothrix
Mould-
thamnidum, cladosporium, penicillum
Yeast-
debaromyces
Proteins- polypeptides->peptides->free amino acids-> ammonia-> hydrogen sulphide, amines- putrefactive spoilage
Carbohydrates- acids (souring spoilage)
Oxidation of fats- fats-> free fattys acids-> aldehydes/ketones (rancidity)
Changed of myoglobin into oxidisied forms- red to grey
What are the different sensory aspects of spoilage?
Unpleasant sensory characteristics are a consequence of accumulation of a mixture of microbial metabolites
First stage- sweet fruity odour (ethyl esters)
Advanced stage- putrid odour (accumulation of sulphur, ammonia and amines)- particularly if psuedomonas is dominant
Ultimately signs of spoilage include meet greening (with or without slime layer)
What does aerobic packaging do to prevent spoilage?
What agent predominantely causes spoilage >5 or <5
What about with minced meat?
Aerobic packaging prevents secondary contamination, doesn’t extend shelf life
At <5d dominant is pseudomonas
At >5d brochotrix thermosphacta more dominant
Minced meat-
poorer microbial status due to higher initial microbial levels, distribution of surface contamination thoughout the product during mincing, higher growth rate due to damaged tissue membranes, finer structure and larger SA
Dominant- psuedomonas and psychotropic enterobacteriacae
How does vaccum packing affect spoilage?
Prevents the growth of aerobes
Proliferation of micro-aerophilic microbiotia in the case of low pH
Lactic acid produces a dairy or cheesy odour/flavour
Shelf life 3 months for beed
Requires- low bacterial level, hygenic handling, pH <5.8, temp lower then 2d
What is the effect of CO2 atmosphere packaging on food spoilage?
Suppresses aerobed
Dissolves in water on meat surface- produced carbonic acic and lowers pH of meat surface
Dominant microbiota on saturated CO2- lactobacillus, leuconostoc, carnobacterium
Eliminated oxidatin of fats- rancidity
100% CO2 causes brown colour of meat (myoglobin)
What does a modified atmosphere do for meat spoilage packaging?
Use of selevted gases with impermeable plastic
O2 and CO2
Generally MAPs for raw meat- 60% CO2, 10% O2, 30% N
Type of spoilage depends on composition
If high level of O2- pseduomonas
If high level of CO2- lactic acid bacteria
Where is meat usually frozen?
How much of the meat is frozen at -5 degrees, -30 and -60d?
When are bacteria and yeasts inhibited?
What is the advantage of rapid freezing?
What are the two main types of spoilage with frozen food?
What is the shelf lifes for different meats?
Normally done in freezing tunnels- -20 to -40 degrees
75% at -5d, 90% at -30d, 100% at -60
Bacteria inhibited at -7 yeasts at -12
Rapid freezing- water inside bacterial cells crystallises leading to cell death
Enzymes concentrated in liquid phase and active in frozen meat
Two types of spoilage- freezing burns and chemical spoilage
Shelf life-
Beef 12m, lamb 8-9m, pork 6-7m, poultry 4-5m, oily fish 2-3m
How is food salted and cured?
Why does it extend the shelf life?
2-6% salt, nitrite
Partly the salt reducing water activity, but interacts with cell components responsible for electron transport, gibes a nice red/pink colour when cooked
Dry curing or injection
How are meats dryed?
What are the three groups?
How are they stored?
Removal of water-
most often keeping the products suspended in the air, lypophilization (freeze drying)- meat is frozen then exposed to low pressure at -20 to -40 removing ice by sublimation
Same volume 70% of the weight
Divided into three groups based on water activity-
High moisture products- 0.9-1- cooked sausage/ham
> 0.95 need to be blow 5d, 0.1-0.95 below 10d, 0.9-0.95 without refrigeration
Intermediate- 0.6-0.9 without refirgeration
Low- <0.6- self stable
What from smoking causes increase in food shelf life?
A result of aerobic or anaerobic pyrolysis of woods and thier polysaccharides, hemi-cellulose and lignin
Starts at 170d and at temps upto 270d is enothermic
Cold smoke 30d, warm 40-60, hot 70-80
Shouldn’t be higher then 300 degrees- carcinogens
What is fermentation?
What causes natrual fermentation and with starter?
What are the products of fermentation?
Fermentation- the phase of intensive growth and metabolism of lactic acid bacteria accompanied with rapid fall of pH
Natural fermentation- aerobic, gram negative flora of chilled meat within 2-3 days replaced by gram positive faculatative anaerobes and micro-aerophiles
More acid-tolerant gram -ves mat persist
Fermentation with starter cultures- course the same but faster
lactic acid producing bacteria
Products- cheese, yoghurt, salami, fermented sausages
What are the three thermal treatments used for extension of shelf life?
Pasturization- water or steam at temperatures below 100 degrees- normally destroys all vegetative cells of microrganisms- spores can survive, can be stored with refrigeration
Boiling- temps over 100 degrees- kills all vegetative forms of microogranisms, not spores, needs refrigeration
Commercial sterilisation- above 100 degrees, usually in pressurised steam autoclaves- spores either killed or injured past germination 121d for 20mins
What factors affect microbial growth?
What are food additives?
- Intrinsic- compisition, physical and biological state
- Microorganisms present
- Extrinsic- temperature, humidity, gases
- Water activity- proportion of available water in food for microorganism need
- adding salt reduces water activity
Food additives
- Polyphosphate- increase ability of meat to bind to water
- Antioxidants
- Food colours
- Preservatives
- Sweetners
- Flavour enhancers
- Emulsifiers
