- Created by: Louise Kay
- Created on: 21-03-11 20:49
What happens when muscle contracts?
- Myosin filaments are drawn towards the 'z' line
- The actin filaments slide over them.
- ATP provides the energy needed for this contraction
Explain how muscle converts to meat.
- Animal is killed/ dies the muscles stiffen which is called Rigor Mortis they remain in this condition for some time
- if the meat is cooked while in reigor mortis it would be tough and in darker colour
- the muscles then soften again ( called conditioning)
- during conditioning the enzymes within the muscle breakdown protein to form amino acids, lipids breakdown into fatty acids
- this leads to the flavour in the meat
- colour changes occur during conditioning going from a reddish colour to brown
- this id due to the myoglobin being oxidised and denatured into metmyoglobin.
- after death ATP is broken down and myosin and actin combine to form myoactine
- glycogen stores in the muscles are broken down into lactic acid which results in a fall in pH
- a higher pH would mean the meat wont keep as welland be prone to microbial damage
- the more glycogen in the muscles before death means the more lactic acide produced and so the pH falls lower
- this affects the taste, texture and keeps quality of the meat.
- a well fed animal will have a higher glycogen stores
- if animal is excited, stressed or fights during death the glycogen stores get depleted.
- sugar feeding is sometimes used to increse glycogen stores before slaughter
Main reasons for cooking meat...
1, improves it's texture (by making it tender)
2, improve it's flavour
3, in improve it's colour
3, improves it's safety (by destroyiong bacteria)
What does over tenderising meat leas to?
An unpleasant flavour and a mushy texture
What is the most effective way of tenderising meat
To inject an anima with PRETEOLYIC enzyme before slaughter. This reduces the time required for conditioning
What are the method used to tenderise meat?
- Mechanical Breakdown - brought by pounding with a heavy object (mallet)
- Adding salt - to increase water capicity
- Sealing the meat - interior cooks less gradually
- Marinating - tenderising, needs acid
What are the chemical and physical changes of musc
- Breakdown of nucleoproteins and similar substances occurs
- Cooking changes colour - causes a brown colouration when cooked
- The protein coagulates and reduces hydration - meat shrinks
- Individual nutrients are affected differently depending upon whether meat was cooked with dry or moist methods
Discuss the storage and handling of meat...
- Game animals, because of there tougher muscle structure need a longer period of conditioning
- Meat must be stored at chilled temperatures to slow down the enzyme changes
- Addition of 10% of carbon dioxide to a chilled storage will extend storage life, but may cause darkening
- chilling meat slows down growth of micro-organisms
- Rigor mortis can lead to excess shrinking and toughness of the meat
How does spoilage of meat occur?
- By infection of fresh and refridgerated meat (mainly from bacteria, moulds and sometimes yeast)
- Meat kept for too long long becomes 'soggy' and PROTEOLYTIC enzymes brown down the protein
- Putrefaction sets in whith production of slime and foul odours caused by PSEUDOMONAS BACILLI
- Fats in meat are oxidised and become rancid which leads to an 'off' flavour
Why does meat darken?
Muscle containsa chemical called myoglobin
when this comnines with oxygen it changes into oxymyoglobin - which gives a red colour
Some bacteria use free oxygen in air to respire
others use oxygen from other sources( anaerobic)
Anaerobic bacteria use oxygen from meat (in oxymyoglobin) turning from red to brown
What are the types of fish?
Oily fish - mackerel, herring, salmon, sardines, trout
White fish (round) - cod, haddock, hake
White fish (flat) - halibut, plaice, sole
Shellfish - crab, lobster, prawns, mussels, oysters, cockels
What is the structural composition of fish?
it is composed of blockes of short, thick fibres (myotomes) in parallel layer
Myotomes are separated by thin sheets of connective tissue (only collagen, no elastin)
Fat in contained in the liver of white fish but distributed throughout flesh in oily fish
Tenderness indicative of the length of fibres
Short myotomes result in tender, flaky fish
Describe the quality of fish...
fish if highly perishable and deteriates quickly
fish muscle contains glycogen and the same rigor mortis occurs as in meat
glycogen is low in poor quality fish, as little lactic acid produced so pH is low giving a soft flesh
fish pass through rigor morits very quickly and bacterial deterioration starts immediately ( to prevent this fish put in ice)
What are the chemical changed which occur in rotti
Fish contain a nitrogen containg compound known was TRIMETHYLAMINE OXIDE
The oxide is removed by bacteria forming TRIMETHYLAMINE ( caused the typical smell)
Proteins breakdown to form amines and ammonia
The unsaturated fats are oxidised to make rancid fats
The typical fish flavour comes from INASINIC acids - this breaks down as fish goes off to form HYPOXANTHINE
What is the nutritional value in meat and fish?
meat- HBV, 20% of weight of lean meat is protein, actine and myosin are main proteins
fish- HBV, 17% cod + herring. 15- 20% weight of lean fish id protein
meat- mainly saturated fat, varable depending on the cut of meat, either visible around edge or contained throughout (marbeling)
fish- white fish if low in fat, present significantly in oily fish (omega3...) low in cholesterol
Carbohydrates- Very low in both
meat- B vitamins (niacin, riboflavin, thiamin)
fish- oily fish - very good source of vitamina A+D+E
meat- excekkent source of iron and heam iron, good source of zinc/potassium/phosphorus
fish- good source of iron but not as good as meat, zinc/potassium/phosphorus (same as meat) good source of calcium (bones)
meat- lower water content
fish- higher water content
Compare the nutritional contribution of meat and f
Both meat and fish are sourves of HBV proteins, both contain no carbohydrates, both are good sources of vitamin B
Fish is low in cholesterol, meat in high in cholesterol (depending on meat) oily fish is a good source of vitamin A and D whereas meat isnt, fish has a high water content whilst meat has a low water content
Describe the structure of muscle in meat...
Muscles are made of myofibril proteins, these proteins are divided into two , actin (thin) and myosin (thick) these proteins are in parallel fibres which vary in length depending on the type of meat. Long fibres make the meat tough. Short fibres makes meat tender.
The fibres are joined by connective tissue which is composed of collegen and elastin (collegen breaks down easier on cooking, elastin doesn't)
Between the paralell fibres are fat deposits (which causes marbeling)
How does meat freeze?
Meat and fish take longer to freeze because of the different tissue structure.
The 'thermal arrest period' will be long - especially in whole fish or a joint of meat
Fish doesn't take as llomg to freeze as meat
A common problem on thawing ins 'drip' (pool of water) because water is drawn from the meat/fish on freezing
What are the different method of freezing meat?
Immersion freezing- fish, immediatly when caught covered with ice
Plate freezing- food packed between two refridgerated metal plates, traps air- fish fingers
Blast freezing- blasting air at high force to freeze- battered fish
Fluidised bed freezing- jets of refridgerated air blasted up onto food- prawns
Cryogenic freezing- liquid nitrogen/ carbon dioxide sprayed directly onto food
Benifits of rapid freezing?
Produces small ice crystals, reduce amound of drip, less damage to structure of food