4 Key foods of animal origin - Pearson

4 Key foods of animal origin

Key termsCoagulation is a form of denaturation and occurs when there is a permanent change in the protein from a liquid into a thick mass as a result of heat, or the addition of acids.

Denaturation describes a permanent structural change of the protein molecules in food. This can occur with the application of heat, mechanical action or the addition of acids.

Homogenisation breaks the globules of milk fat into minute particles so that the cream does not rise to the surface of the milk.

Membrane technology involves using a porous membrane or filter to separate the particles in a fluid. Two of the most commonly used forms of membrane technology in food production are ultrafiltration and reverse osmosis.

Origin is the original source of a particular food.

Pasteurisation (HTST) destroys pathogenic or disease-causing bacteria and also extends the shelf life of milk. The milk is heated to 72 ºC for 15 seconds and then is cooled rapidly to 2 ºC.

Physical properties are a particular trait such as size, viscosity or shape.

Primary processing involves a range of processes to make food safe to eat so that it can be consumed individually or used in the manufacture of other food products. The physical form of the food changes very little.

Reverse osmosis is a form of membrane technology similar to ultrafiltration but the pores in the membrane are smaller and allow only water to pass through, leaving behind concentrated milk solids.

Secondary processing refers to turning primary-processed food into other food products, either on their own or mixed with other ingredients. The physical form of the original food can change quite significantly.

UHT refers to processing milk at higher temperatures than for pasteurisation, but for a much shorter time, killing all bacteria in the milk, including those that turn milk sour.

Ultrafiltration is a form of membrane technology in which milk is pumped across a membrane to collect the protein and fat and some of the calcium molecules, but the water and lactose are allowed to pass through.

Food Solutions 3&4_04.indd 55Food Solutions 3&4_04.indd 55 22/07/10 3:40 PM22/07/10 3:40 PM

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Cow’s milk is a white, opaque liquid

which contains almost three times more protein

than human milk.

Sheep’s milk has a much higher fat content

than cow’s milk, providing almost twice the fat content. This high fat

content gives it a sweeter and richer flavour and much

whiter colour.

Goat’s milk is sweeter and whiter in

colour than cow’s milk. Its nutritional composition

is similar to cow’s milk.

56 Food Solutions Units 3 & 4

Dairy foods

MilkMilk is a liquid produced by mammals to feed their young. It consists mainly of water and a range of nutrients, including various proteins, calcium, milk fat, sugar, vitamins and mineral salts that are suspended in the liquid. Milk is the main ingredient in the production of all dairy foods.

Physical and sensory properties of milkCow’s, goat’s and sheep’s milk are most commonly consumed by human beings. Cow’s milk is the most popular source of milk in Australia—we consume approximately 102 litres of cow’s milk per capita per year.

Nutrient content of milk• Protein—The protein in milk is complete protein,

containing all 22 essential amino acids. Milk contains many different types of protein, which can be divided into two main kinds: those present in the whey of the milk, principally lactoglobulin and lactalbumin; and those present in the curds of the milk, casein. This classification of the proteins in milk is important, particularly in cheese making.

• Fat—Whole milk contains tiny globules of saturated fat, which are suspended as a fat-in-water emulsion. They give milk its characteristic taste and smooth texture. Whole milk also has a high level of cholesterol, due to the amount of saturated fat it contains. If milk is not homogenised and is left to stand, the fat globules form into a cream layer on the surface of the milk. Milk that has a high butter-fat content produces the best cream and cheese.

• Carbohydrate—Milk contains the sugar, lactose, which has a slightly sweet flavour. Lactose is far less sweet than sucrose, the sugar found in sugar cane. It is also easily converted to lactic acid by the action of bacteria naturally present in milk, which causes milk to sour. Lactose also has a low solubility level and is responsible for the gritty taste sometimes found in ice-cream and condensed milk.

• Vitamins—Milk contains most of the key vitamins, especially the fat-soluble Vitamins A and D, which are present in the fat in the milk. Vitamin A gives whole milk its slightly yellowish colour. Milk is also a valuable source of riboflavin or Vitamin B2 but this is easily destroyed by exposure to sunlight. Thiamine or Vitamin B1 is also present in small quantities, but this vitamin is also easily destroyed by heat and sunlight. There is very little Vitamin C present in milk.

• Minerals—The main mineral found in milk is calcium, which is essential for the building of strong bones and teeth, and preventing osteoporosis. The calcium present in milk is easily absorbed by the body, more so than calcium from vegetable origins. Health authorities suggest that it is difficult to meet our daily needs for calcium without including some dairy foods in our diet. Milk also contains a valuable supply of phosphorus, but is very low in iron.

• Water—Milk is made up of 87 per cent water.

Sources of milk


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Chapter 4 • Key foods of animal origin 57

Dairy products made from milk

Dairy product Varieties Reason for production

Liquid milk • Whole milk• Low fat, increased calcium

• Vitamin D, fibre, Omega-3 or plant sterol enriched• UHT• Flavoured milk

• Popular, healthy, economical drink• For consumers concerned about reducing

weight or preventing osteoporosis• To meet specific health needs of consumers• UHT extends shelf life without refrigeration• Consumer appeal—marketing opportunity

Concentrated milk • Evaporated• Sweetened condensed

• Reduces bulk• Extends shelf life

Powdered milk Full-cream or skim • Reduces bulk• Extends shelf life

Buttermilk Natural • Slightly thickened texture and mild, tangy, sharp or acidic flavour

• Assists in leavening some baked products by creating a lighter texture than milk

Milk proteins Casein and caseinates • Ingredient in smallgoods, bakery items, non-dairy creamers and whipped toppings

Yoghurt Natural set, flavoured, low fat • Increased consumer demand for products, which improve health—probiotic

Cream Light, reduced fat, thickened, whipping, pure • To meet consumer demand for appealing sensory properties—smooth, creamy, rich mouth-feel

Butter • Regular

• Reduced or low salt, dairy blends and spreads

• For cooking, especially baking cakes and biscuits

• To meet consumers’ health needs

Ice-cream • Premium, bulk, iced confections

• Low fat

• Easy dessert options• Popular snack food• To meet health needs

Cheese Fresh, soft, firm, hard • Adds variety to diet• Concentrated source of protein and calcium• Used in many food products• Some varieties extend shelf life of milk

Products made from milk

Processing milkMilk is a highly perishable food as it is an excellent medium for the growth of micro-organisms. It is essential that attention is paid to food safety factors, particularly temperature controls, throughout all stages of processing in the supply chain to deliver safe dairy foods to consumers. Developments in membrane technology have allowed milk manufacturers to make the sensory and chemical properties of milk more appealing to consumers and to meet their health needs.

PasteurisationMilk is pasteurised using the High Temperature Short Time (HTST) process. This involves pumping the milk continuously through heat exchangers to shock-heat the milk to 72 °C. It is held at this


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temperature for 15 seconds and then shock-cooled to 2 °C. This process kills disease-producing bacteria (pathogenic bacteria) such as those that cause tuberculosis. Pasteurised milk is therefore safer to drink and keeps longer than untreated milk. This process does not reduce the nutrient value of milk and has minimal affect on the flavour.

UHT (Ultra High Temperature)This process uses higher temperatures than for pasteurisation, but for a much shorter time. A temperature of 135 °C is used for 2–3 seconds. This high temperature kills all bacteria in the milk, including those that turn milk sour. The milk is then sterile and is packed into sterile, plastic-lined cardboard containers and sealed in a sterile environment to prevent contamination occurring. This method of packaging is called the ‘aseptic packaging system’. UHT milk can be stored for 3–6 months without refrigeration.

HomogenisationWhen unhomogenised milk is allowed to stand for a period of time, the cream floats to the surface. The process of homogenisation can slow this separation down by making the fat globules smaller without changing the nutritional composition of milk. This process is carried out by forcing the milk through small nozzle-like openings or between closely positioned plates. Some of the advantages of homogenising milk are:

• uniform distribution of fat, so there is no cream layer

• more full-bodied flavour

• whiter, more appealing colour

• faster coagulation in the manufacture of cheese.

Membrane technologyMembrane technology is widely used in the dairy industry as a means of producing a range of milk products to meet specific consumer needs. Reduced-fat milks and those with increased levels of protein or calcium are all popular products with consumers.

Filtration membranes, normally made from a thin polymer or plastic material, are used to separate the natural components of milk without changing them chemically. The milk is pumped over the membrane under pressure to separate out the dissolved solids from the milk fluid.

There are two main types of membrane technology used in milk processing: ultrafiltration and reverse osmosis.

• Ultrafiltration—Milk is pumped across a membrane, which collects the protein and fat and some of the calcium molecules, and allows the water and lactose to pass through. This process is used in the production of high protein/high calcium milks such as PhysiCAL and Rev. It is also used to recover protein from the whey in cheese manufacturing and the resulting concentrated protein is used as an ingredient in other products.

• Reverse osmosis—This process is similar to ultrafiltration, but the pores in the membrane are smaller and allow only water to pass through, leaving behind concentrated milk solids.

Membrane

Whole milk

Milk lowerin protein,fat and calcium

Fat globules beforehomogenisation

Fat globules afterhomogenisation

Changes in the size of fat globules in milk after homogenisation

Milk passing through filter membrane


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Curd formation—Starter culture is added to treated liquid milk. The acid that is produced causes the protein to clot. The enzyme rennet assists in curd formation by coagulating the protein.

Syneresis—The curd is gently heated so it shrinks and toughens, and the whey is expelled.

Milling—Curd is cut into small, even-sized pieces.

Salting—Salt inhibits bacterial activity, contributes to flavour development and helps to firm the curd.

Moulding—Cheese is pressed into shape.

Maturation—The cheese is stored in a cool environment to develop the flavour and texture. The longer the time, the sharper the flavour and the crumblier the texture.

Packaging and labelling—The cheese is packed, often using MAP, to extend its shelf life and is labelled according to FSANZ Food Standards Code.

Secondary processing:Cheese making

Cheese is a concentrated dairy food, which contains many of the nutrients found in milk. The following stages in cheese processing are common to all groups; however, there will be differences within each depending on the type of cheese being made.

Analysis—Before collection, milk is analysed for micro-organisms and butter fat content.

Membrane technology filtration—Liquid milk is passed through specialised filters to standardise or alter nutrient composition.

Homogenisation—Liquid milk is forced under pressure to break down fat globules and evenly distribute cream to create a smooth, creamy texture.

Packaging or secondary processing—Liquid milk is packaged and distributed to retail outlets, or it becomes the main ingredient in dairy products such as cheese, yoghurt and ice-cream.

Pasteurisation—Heat treatment (HTST) kills bacteria and spoilage micro-organisms.

Primary processing of milk

Milking of cows—Milking is undertaken using automated milking machines; fully automated, robotic systems are becoming more widely used on dairy farms.

Collection of milk—Milk is chilled rapidly on the farm and held in refrigerated vats.


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Cooking with milk

Heating milkWhen milk is heated in a saucepan, several changes occur. Some of the water in the milk evaporates as steam and the tiny globules of fat begin to rise to the surface, giving a more creamy appearance. When the temperature of the milk reaches boiling point (100 °C), the proteins present on the surface of the milk combine with the fat to form a skin. If the heating continues, the milk may boil over as a result of the pressure of steam forcing its way through the skin.

If milk is warmed over a direct heat, a coating forms on the base and sides of the saucepan. This occurs as the heavy protein particles in the milk fall to the bottom of the saucepan, where they stick and can scorch or burn. This effect is even more obvious in functional milks that have been enriched with additional protein or calcium. To help prevent this, stir the milk during heating, or use a heavy based, non-stick pan or heat in a microwave oven.

Combining eggs with milkCustard is a mixture of milk, or milk and cream, with eggs or egg yolks and sugar. There are two basic kinds of custard: one is stirred on top of the stove and the other is baked in the oven.

The consistency of custard depends on the proportion of eggs to milk—the higher the ratio of eggs to milk, the thicker the end product. The smooth texture of custard relies on gentle cooking, ensuring the eggs coagulate or set evenly within the milk at a temperature between 65 °C and 70 °C. Preparing a

stirred custard in a double boiler, or cooking the set custard in a water bath, helps to prevent the delicate mixtures from curdling or separating. If the custard is overheated, the proteins from the egg and milk begin to over-coagulate to form small lumps and separate from the whey, and the smooth, rich texture is lost.

Combining an acid with milkIngredients such as citric acid, for example, lemon juice, cause significant change in the sensory properties of milk when they are mixed together. Adding lemon juice to fresh milk will cause the milk to curdle. This means the milk protein, casein, joins together or coagulates to form tiny lumps or clots, thus altering the texture and appearance of the milk. The flavour of milk also becomes sour to taste. The hot dessert lemon delicious utilises the ability of the milk protein to clot and thicken when mixed with an acid to create its unique texture.

Understanding the text 1 Draw a knowledge map to summarise the

nutrients in milk and their impact on good health.

2 Milk is the basis of dairy products. Select four groups of dairy products, record the varieties available and explain why the products are available for consumers to purchase.

3 Describe the method used to pasteurise milk and explain why the process is used.

4 What is UHT and why is this process used in milk production?

5 Briefly describe the process of homogenisation and list some of the benefits of this process.

6 What is membrane technology? Identify and describe two examples of membrane technology used in the production of milk products.

7 Identify and describe three key steps in the primary processing of milk.

8 Draw a flow chart to explain the effect of heating on milk.

9 Explain why a milk and egg custard should be heated over water to achieve the most desirable sensory properties.

10 Describe the changes that occur when lemon juice is added to milk.

Some particles oflactalbumin, casein andcalcium salts fall tobottom and can catchand burn

Some water content isevaporated as steam

Proteins lactalbumin andlactoglobulin form a skinon the surface

Tiny globules of fatrise to the surface

Heating milk


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EggsEggs are a self-contained food that provides many nutrients. Usually in cookery, the reference to eggs means hen’s eggs. They can be cooked simply by a range of methods or can be incorporated into a wide variety of recipes.

Physical and sensory properties of eggs

Nutrient content of eggsEggs are an excellent source of protein. They are low in saturated fats, but their cholesterol level is of some concern to people on low-cholesterol diets. Eggs provide B vitamins, especially B12, Vitamins A and D, iron and phosphorus. Cooking does not significantly alter their nutrient value. The colour of the shell and the farming methods used to produce eggs does not influence the nutrient value of eggs, although they may influence the flavour and the colour of the yolk.

Some eggs are enriched with additional nutrients by feeding hens a specially formulated diet. In the case of eggs with a higher level of Omega-3, the laying hens are fed a special diet, which may include fish and fish oil, canola oil, soya bean oil and flaxseed. All of these products contain high levels of the polyunsaturated fatty acid Omega-3 and if included in the hens’ feed, result in eggs with a higher level of Omega-3 than eggs from hens on a traditional diet. Research has found that Omega-3

helps lower blood triglyceride levels and so prevent heart disease. It is also necessary for normal growth and development of the brain, eyesight and the nervous system.

Cooking with eggsIn each protein food, including eggs, all the molecules are identical in shape. If the natural shape of the protein is altered by heating, exposure to acid, or by mechanical means, it is said to be ‘denatured’. As it is possible to denature egg protein in a variety of ways, eggs are a versatile ingredient in food preparation.

Heating—coagulation of eggsDuring cooking, heat is applied to eggs or egg mixtures, causing considerable changes in their physical properties. In its raw state, egg white is a clear liquid with a slimy texture and egg yolk is a dense yellow colour and is slightly more viscous than the white. When the egg is exposed to heat, the liquid white gradually sets to form a white rubbery mass and the yolk becomes firm. This denaturation of the protein sets the eggs and is termed ‘coagulation’. Egg white and egg yolk coagulate at different temperatures; egg white at 62 °C–65 °C and egg yolk at 65 °C–70 °C.

Yolk Germinaldisc

Membranes

Shell

Air sac

Chalaza

Thick white

Thin white

Structure of an egg

Acid

lowerscoagulationtemperature

poached egg

Heat

coagulation

boiled egg

Mechanical means

whisking orbeating

soufflé

Sugar

increasescoagulationtemperature

baked custard

Denaturing eggs during food preparation

Denaturing eggs during food preparation

Egg yolk65°C–70°C

Egg white62°C–65°C

Coagulation temperatures


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The temperature at which egg protein coagulates or sets is dependent on several factors:

• Concentration—In a recipe, the dilution of egg proteins increases the temperature at which the proteins coagulate. For example, a custard made with one whole egg thickens at a lower temperature than one made with only the egg yolk.

• Acid—Adding acid to egg white decreases the pH so the proteins become less stable and more likely to denature. This means small amounts of acid lower the coagulation temperature of most egg proteins. For example, adding vinegar to the water when poaching eggs causes the egg white to set more quickly and to hold its shape.

• Sugar—Adding sugar raises the temperature of coagulation of an egg mixture.

Mechanical means—whisking or beating eggsWhen egg whites are whisked or beaten, the protein is denatured, creating a foam that will aerate a mixture. As the egg white is beaten, the protein is stretched, forming a thin membrane that traps air bubbles. This mesh-like structure stabilises the air bubbles in the foam. Providing protein molecules are not overstretched, the foam will continue to expand when heated, creating extra lightness. Examples of this form of aeration can be observed when sponges and souffles are baked and fluffy omelettes are cooked in a frying pan.

Adding salt to eggsWhen beating an egg white, a pinch of salt may be added to help create a more stable, stiff foam without influencing the flavour as it helps to bring the proteins together. Both the salt and the beating action contribute to the denaturation of the egg protein.

Adding acid to eggsWhen eggs are poached in hot water, a small amount of acid in the form of vinegar can be added to assist in the denaturation process. Combining heat and an acid helps to denature the egg protein so it coagulates and holds its shape at a lower temperature, making the end product more appealing. However, if the water is allowed to boil when poaching eggs, the rapid movement of the

bubbles in the water causes the delicate egg white to become ragged and misshapen.

Understanding the text 11 Name the structure that anchors the yolk

in the centre of the egg.

12 List the main nutrients in eggs.

13 Explain how eggs can be enriched with Omega-3 and explain why consumers would purchase them instead of traditional eggs.

14 Define the term ‘denaturation’ and identify the different ways egg proteins can be denatured.

15 Use a flow chart to illustrate the physical changes in egg protein as it begins to coagulate.

16 Explain why you would have to adapt the cooking time when baking a custard made with two egg yolks rather than two whole eggs.

17 Explain how beating eggs denatures the proteins and aerates a mixture.

18 List four examples of products, other than those listed in the text, which are based on the aeration of egg white.

19 Why is a pinch of salt added when beating egg white to a foam?

20 Why is vinegar added to the water when poaching an egg?

MeatMeat is the flesh of animals and birds that is eaten by humans. Red meat includes flesh from cattle (beef) and sheep (lamb). White meat encompasses flesh from pigs (pork), calves (veal) and poultry (chicken, turkey and duck). Game is dark meat that may come from rabbits, kangaroos, crocodiles, deer and wild birds.

Physical and sensory properties of meatLean meat is composed of bundles of long muscle fibres. Each fibre has a wall of elastin and is filled


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with water carrying dissolved protein, minerals and extractives. These fibres create the grain of the meat. The bundles of fibres are held together with collagen, which dissolves into gelatine during wet cooking.

Fat is present between the fibres in the form of invisible fat or marbling, on the outer surface as adipose tissue, and around the internal organs such as the kidneys, where it acts as a protective layer. The older the animal, the greater the amount of fat.

What makes meat tender?The tenderness of a cut of meat depends on the age of the animal and the part of the body from which it comes. The meat from young animals has short, fine fibres, whereas meat from older animals has longer, thicker fibres and more connective tissue. The level of activity of an animal is directly related to the tenderness of its meat. Hard-working muscles of an animal’s legs and neck are highly developed, so there is a greater build-up of hard connective tissue—the resulting cuts of meat are tougher, darker in colour and have a stronger flavour. The cuts of meat from around the ribs, the back and the rear parts of the animal that move less when the animal is in the pasture produce the most tender cuts of meat.

The tenderness of meat is influenced by the methods of preparation and cooking used, as well as the cut selected. Meat can be partially tenderised mechanically by scoring or pounding or cutting across the grain. It can also be tenderised by marinating.

Musclefibre

Meatjuices

Elastin

Fat cells Connective tissue(collagen)

Tendon (connectingmuscle to bone)

Outer connective tissue

Bundle ofmuscle fibres

Connective tissuesurrounding bundleof muscle fibres

(a) (b)

Structure of meat

Beef1 The rib of the beef is a tender cut of meat and produces the rib-eye steak and rib-eye roast.2 The lean, tender cuts of sirloin steak and T-bone steak and the premium cut of eye fillet come from this area.3 The rump can be cut into steaks or a roast.4 The silverside and topside cuts are less tender and are best cooked by wet methods.

Pork1 The most tender cuts of pork are from the loin and provide loin chops, a rack of pork, loin cutlets and pork fillets.2 The rump of pork is usually roasted.

Lamb1 The shoulder is a tougher cut of lamb and can be roasted or casseroled.2 The rib loin is a very tender cut of meat. The rack of lamb, cutlets and rib chops are from this section.3 The fillet and eye of the loin is the most tender and expensive cut of lamb.4 The leg of lamb can be roasted whole or cut into steaks.

1

1

1

2

2

2

3

3

4

4

Cuts of meat—beef, lamb, pork


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Nutrient content of meatThe important nutrients in lean red meat are protein, iron, zinc, Vitamin B12 and some fats. Humans require about 40–50 grams of protein per day for growth and repair of muscles, skin, enzymes and hormones. This amount can be obtained in an average-size serve of steak (100–125 grams) and a piece of cheese. Any extra is converted to kilojoules which, if not used up in physical activity, are stored as body fat.

During the cutting process of the meat carcass, adipose fat is trimmed from the outside, but the marbled fat is eaten along with the muscle tissue.

Today, meat is being bred and sold with less fat. Australian pork cuts have 40 per cent less fat than conventional cuts, and lamb is up to 60 per cent leaner than lamb bred 20 years ago. Red meat that has been trimmed of visible fat is nutritious and as low in fat as white meats such as pork, veal and chicken. Raw, lean meat contains about 70 per cent water, which reduces considerably after cooking.

Cooking meatCooking meat successfully is all about producing the right textures and flavours. Meat is cooked to make it safe to eat and easier to chew and digest, and to destroy any harmful micro-organisms. Methods of cooking can be divided into two groups—dry and wet methods.

• Dry method of cooking—This is a fast way of cooking meat that is best suited to tender cuts of meat. These cuts of meat have enough water present in their tissue to enable the conversion of the protein, collagen, to gelatin. Therefore, this method uses little to no liquid and the time taken to cook the meat depends on the size and thickness of the cut. Examples of this method are pan-frying, stir-frying, grilling, barbecuing and oven-roasting.

• Wet method of cooking—This is a slow way of cooking meat that is suitable for less tender cuts of meat. These cuts do not have enough water present in their tissues to convert collagen to gelatin. Therefore, the long, slow, wet cooking softens the connective tissue that makes meat tough. Examples of this method are stewing, casseroling, pot-roasting and braising.

Protein

Iron

Zinc

Vitamin B12

Fats

Nutrients in lean, red meat

Cooking meats

Cooking method Beef Lamb Pork

Tender cuts—suitable for quick, dry methods of cooking

Rump, fillet, Scotch fillet, porterhouse, T-bone, marinaded blade

Boneless leg steaks, cutlets, loin chops, chump chops, fillet

Fillet, butterfly steaks, schnitzel, cutlets

Tougher cuts—preferable for wet, slower cooking methods

Blade, chuck, shin on the bone, osso busso

Shoulder, shank Forequarter

Roasting is a dry heat method used to cook larger, tougher cuts of meat

Topside, piece sirloin, piece Scotch fillet, standing rib roast, rolled rib roast

Leg, shoulder Leg, shoulder, loin, rack, rolled and boned loin pork


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Changes that occur when meat is cookingThe cooking process changes each main structural component of the meat:

• Muscle fibre—During heating, the proteins in the muscle fibre begin to change shape (denature). As the proteins change, there is contraction in the direction of the muscle fibre, resulting in the piece of meat shrinking and becoming hard. The longer the meat is heated, the tougher it becomes, as more protein is denaturated. If meat is overcooked, the toughened protein becomes less digestible.

• Connective tissue—The tough collagen, which makes up connective tissue, must be cooked sufficiently to convert it to water-soluble gelatine so that it becomes tender enough for us to bite through.

• Fat—Before heat is applied, the fat in meat is solid, either on the edge of a cut or marbled through the muscle fibre. During cooking, the fat melts and acts as a lubricant so that the muscle fibre appears less tough. Fat also contributes to the flavour and aroma of cooked meat.

• Water—This is the largest component of meat and has a major influence on the flavour and texture of the cooked meat. When the meat is heated, for example, in frying, a little water will flow out of the meat as the proteins begin to denature. However, most of the water remains locked within the proteins, and if the meat is cooked at the correct temperature and for the correct time, it should be juicy and moist to eat. Meat that has been cooked too long will become dry because the water has been lost.

Cooking timesThe cooking time required for meat depends on both the cut of meat and the cooking method selected. Tougher cuts of meat have a greater ratio of connective tissue to muscle fibre, and therefore require long cooking times, whereas tender cuts, which have a lower ratio of connective tissue to muscle fibre, should be cooked for a short time.

Developing the sensory properties of meat during cooking• Texture—Cooking improves the palatability of

meat by making it easier to chew. When heat is applied, the protein in the meat is denatured and coagulated. It also shrinks as some of the water is expelled and the texture becomes firm. Connective tissue is tenderised and the collagen is converted to gelatin, if moisture is present. The fat melts, giving meat a crisp brown surface.

• Colour, flavour and aroma—When meat is cooked at high temperatures, a series of chemical reactions develop the flavour and meaty aroma associated with cooked meat. The Maillard reaction contributes to the dark brown surface colour. The melting fat from the meat also contributes to flavour when it is cooked. The colour of meat changes from red to brown.

Cooking times for meat

Type of meat Examples of cuts Cooking time

Meat with small amounts of connective tissue

Middle loin lamb chops or lamb back straps

Grill for only 5–10 minutes

Meat with large amounts of connective tissue

Blade steak used in a curry Simmer gently for 1.5–2 hours

Stages in the cooking of meat

70°C—meat grey colour—coagulation almost complete, water bound in the protein stops.

Inside the meat80°C–90°C—meat light brown, heavy, firm-textured meat.

Outer surface130°C—temperature required for the Maillard reaction to occur to brown meat.

40°C–50°C—meat red colour—muscle proteins begin to denature, coil up and shrink; water bound in the protein begins to flow.

60°C—meat pinky colour—coagulation occurring.


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PoultryThe term ‘poultry’ includes duck, turkey, chicken, pigeon and goose. Chicken is the most popular type of poultry because it has an appealing flavour, can be prepared and cooked in many different styles and is economical.

Production of chickens in Australia is a highly mechanised process. The environment of the chickens is controlled; that is the temperature, lighting and the size of their cage. As the amount and type of feed they consume is monitored, chicken meat is produced in a given time and is of a standardised quality. Chicken is available fresh or frozen.

Since the 1980s, there has been increasing concern from consumers and animal welfare groups about the intensive system of production. In response, some poultry farmers have reverted to the traditional method of allowing the chickens to range outdoors in daylight hours and eat a variety of grain and green foodstuffs. Chickens produced in this manner are known as ‘free-range’ chickens and are available fresh to consumers.

Nutrient content of poultryPoultry has the same amount of protein as red and other white meats, less saturated fat and more polyunsaturated fat. The fat content varies depending on the type of fowl, the breeding method, the cut and whether the skin is eaten. It is a good source of zinc and magnesium, and a moderate source of iron.

Structure of poultryPoultry can be cooked as a whole bird, or cut into portions such as thigh fillets, drumsticks, wings, tenderloins, chops and breast fillets. The thigh and leg meat of poultry is from the active muscles of the bird, so these are tougher cuts. They are darker in colour because they require more oxygen to move about and are higher in fat. Domestic chickens do not fly, so their breast meat is white and tender because there is less connective tissue. The tender cuts such as tenderloins and breast fillets are best prepared using quick methods of cooking such as stir-frying or pan-frying to prevent dryness and toughness. Tougher cuts such as drumsticks and thighs have more connective tissue and are best baked or cooked using a wet method such as a curry or casserole.

SeafoodFish are aquatic vertebrates; that is, they have a spinal column and are found in fresh water or salt water. Fish are one of the most popular animal foods eaten throughout the world. They are found in most waterways of the globe, from the waters of the Arctic and the Antarctic to tropical streams and oceans.

Physical and sensory properties of seafoodFish is different from meat and poultry in that the muscles are arranged in layers of short fibres unlike the long fibres that make up the muscle fibres of meat and poultry. These bundles of short fibres are surrounded by very thin sheets of delicate connective tissue. Fish contains very little connective tissue—only about 3 per cent of its body weight in comparison with meat, which contains approximately 15 per cent of connective tissue. The little connective tissue that is present is very fragile and easily converted to gelatine.

Fish can have differing sensory properties depending on the amount of oil in their flesh.

• Oily fish—The oil is dispersed throughout a darker coloured flesh and they have a strong flavour. Examples of oily fish are salmon, tuna, trout, sardines, mackerel and gem fish.

• Fish in the white classification—These fish have white flesh and a delicate flavour, and the

Muscle fibres in fish

Muscle blocks

Muscle blocks

Connective tissue

Scales


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oil is contained in a small sac near the liver. Whiting, flathead, flake, garfish and bream are in this group.

The changes in the physical and sensory properties of fish are very evident during the cooking process. In its raw state, fish is translucent, firm to touch and the juices are clear and watery. Fish is fully cooked when the flesh becomes opaque, the flakes just begin to separate and the juices are milky white. Fish cooks quickly and, when cooked, it is very tender, with a tendency to fall apart during cooking. As fish has a low fat content, it is easier to digest than meat or poultry.

Chemical properties of seafoodFish has a high water content and is rich in protein—70 per cent of the flesh of fish is composed of water and 20 per cent protein. The fat in fish is a good source of Omega-3 oils, which are beneficial for health, particularly in the prevention of heart disease. Omega-3 oils have been shown to keep blood free-flowing, to slow down the build-up of fatty material on the walls of blood vessels and to make the arteries more elastic. Omega-3s are found in all fish and seafood. Oily fish are the best sources.

Dieticians recommend eating fresh fish regularly and if it is not easily available, canned salmon, tuna or sardines are an alternative. Prawns, fish roe, calamari and octopus should be eaten in moderation and fried fish in batter and anchovies should be eaten occasionally as they are higher in saturated fat.

Understanding the text 21 What is the grain of meat?

22 Where do the most tender cuts of meat come from on animals and what are the recommended cooking methods?

23 Identify the main nutrients in meat and discuss the value of each nutrient as a food source for humans.

24 Why are dry methods of cooking suitable for some cuts of meat and wet methods for other cuts of meat?

25 Prepare a summary of the changes that occur during cooking to the main components of meat—muscle fibre, connective tissue, fat and water.

26 What factors influence the cooking time for meat?

27 How does cooking change the sensory properties of meat?

28 Explain the similarities and differences in the nutrient value of red meat and poultry.

29 Discuss the relationship between tenderness and cut in poultry.

30 Describe the difference in structure between fish and meat, and explain how this impacts on the cooking time of fish.

Preparing for examsApplying knowledgeDraw a knowledge map to illustrate the functional role eggs can play in food products. Include an example of a product produced using each of the functional properties identified.

Analysing informationAnalyse the changes in the physical structure of meat when it is cooked. Use a simple diagram to support your analysis.

Evaluating conceptsEating tender meat is an enjoyable experience for most people. To maximise the tenderness of meat, it is essential to match the cut of meat and the cooking method. Identify two cuts of meat from different animals that can be cooked quickly and recommend an appropriate cooking method. Justify your answer in the terms of the physical structure of the meat.


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Production 4.1Cooking with eggs and milkThis delicate dessert demonstrates some of the functional roles that the key foods milk and eggs play in a recipe. During the preparation process, both ingredients are denatured by heat, acid or mechanical means. This recipe also incorporates two dry methods of cooking—frying and baking.

Lemon soufflé crêpes

Crêpes½ cup plain flour

¼ teaspoon salt

2 eggs

½ cup milk

10 grams butter

Lemon soufflé30 grams butter

1 tablespoon plain flour

4 tablespoons milk

2 egg yolks

2 tablespoons caster sugar

2 teaspoons lemon rind

2 tablespoons lemon juice

2 egg whites

Method

Making the crêpes 1 Sift the flour and salt. 2 Beat the eggs and pour into the centre of the flour. 3 Gradually beat in the eggs and half the milk. 4 Beat well for 1 minute. 5 Stir in the remainder of the milk. Allow to stand for 30 minutes

if possible. 6 ‘Burn off’ the frying pan by melting a teaspoon of the butter and

allowing it to come to smoke point. Remove the pan from the heat and wipe out carefully with paper towel.

7 Using a fresh piece of paper towel, wipe a little butter onto the pan and return to the heat. Adjust heat so the butter does not burn.

8 Pour ¼ cup of the batter quickly into the pan and swirl so it forms only a thin layer in the pan.

9 Cook until just set. Toss the crêpe and cook the second side. 10 Place on a plate and cover with foil or a clean tea towel to keep warm. 11 Cook the remaining crêpes, remembering to wipe the pan with a little

butter between each crêpe. This should make 6–8 crêpes.

Making the soufflé 1 Preheat oven to 200 ºC. 2 To make the roux for the base of the soufflé, melt the butter in a small

saucepan. Remove from the heat and stir in the flour with a wooden spoon.

3 Stir in the milk and beat vigorously over a low heat until the mixture boils and thickens.

4 Remove from the heat and beat in the egg yolks immediately. 5 Add 1 tablespoon of the caster sugar, the lemon rind and the lemon

juice and stir until the ingredients are well blended. 6 In a clean bowl, beat the egg whites until soft peaks form. 7 Gradually beat in the remaining 1 tablespoon of caster sugar until stiff

peaks form. 8 Stir a tablespoon of the egg white into the soufflé base using a rubber

spatula. 9 Lightly fold in the remainder of the egg white. Do not overmix.


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Assembling the lemon soufflé crêpes 1 Carefully separate the crêpes and lay one, speckled side up, in a

shallow, ovenproof dish or tray. 2 Place approximately 2–3 tablespoons of the soufflé mixture on one

side of the crêpe. Fold the crêpe in half to cover the soufflé mixture. 3 Place a second crêpe in the baking dish and fill with lemon soufflé.

Repeat the process until all crêpes are filled. 4 Sprinkle crêpes with a little extra sugar. 5 Bake in the preheated oven at 200 ºC for approximately 10 minutes

until the soufflé has puffed and the sugar has melted to a light glaze. 6 Serve immediately with cream or vanilla ice-cream.

Serves 2–4

EVALUATION

1 Why is it important to only add half of the milk with the egg in step 3 when making the crêpe batter?

2 Why is the batter left to stand in step 5 when making the crêpes? In your answer, focus on the physical properties of the starch in the flour.

3 Making the crêpes for this dessert is a complex process. Explain the decision you took in each of the following steps and how it helped you to achieve a successful product:• the preparation of the crêpe pan• creating even-sized crêpes.

4 Explain the difference between the cooking terms ‘beating’ and ‘folding’.

5 How does the lemon juice affect the milk and eggs in the soufflé recipe?

6 Describe how the proteins are denatured when beating the egg whites to create a foam for the soufflé.

7 The preparation of the soufflé filling is another complex process in the production of the lemon soufflé crêpes. Explain the decision you took in each of the following steps in the soufflé filling and how it helped you to achieve a successful product:• making the roux base for the soufflé filling• beating the egg white.

8 Discuss the changes to the properties of the lemon soufflé crêpes during baking.

9 Identify several safety considerations when frying the crêpes and baking the finished product.

10 Describe the sensory properties—appearance, aroma, flavour and texture—of the lemon soufflé crêpes.


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Production 4.2Preparing a summer meal on the cook topThis Asian-style salad makes a delicious summer meal. The preparation of this recipe demonstrates the denaturation of protein that occurs when heat is applied and the effect of cooking on the sensory properties of poultry. It also incorporates the wet cooking methods of boiling and blanching and the dry cooking method of pan-frying.

Method 1 Remove the skin from the chicken fillet. Place between plastic wrap

and roll with a rolling pin until even thickness. Spray or brush lightly with vegetable oil.

2 Prepare chargrill pan or frying pan and cook fillet until just cooked. 3 Remove from heat, wrap in foil and allow to rest for at least 10 minutes

before slicing thinly across the grain of the fillet. 4 Prepare the vegetables. Blanch and refresh the capsicum, snow peas

and carrot individually in fresh water. 5 Separate the noodles and place in a large bowl. Cover with boiling water

and stand for 5 minutes. Drain and rinse under cold water. Drain well. 6 Mix all the dressing ingredients in a screw-top jar and shake, or whisk

in a small bowl until combined. 7 In a large bowl, combine all the vegetables, chopped chicken, noodles,

mint and coriander with dressing. Toss gently so the dressing coats all the ingredients. Serve immediately in a bowl or take-away noodle box.

Serves 1

EVALUATION

1 Explain how you would assess the quality of the ingredients when selecting the chicken and vegetables for this recipe.

2 Describe the changes that occur in the protein molecules of the chicken fillet while it is being pan-fried.

3 Discuss the effect on the sensory properties of resting the chicken before cutting and slicing it across the grain in step 3.

4 Why were the capsicum, snow peas and carrots blanched in this recipe?

5 What might happen if the noodles were boiled on the cook top, rather than just covered with boiling water?

6 The dressing is an example of an emulsion. What is an emulsion and why is it added just prior to serving?

7 Suggest some alternative vegetables you could use if spring onions, red capsicum, snow peas, carrot and bean shoots were not available.

8 Describe the safe work practices you followed to prevent cross-contamination between ingredients when preparing this recipe.

9 Describe the sensory properties of the chicken noodle salad.

10 Make some suggests for improvements to this recipe if you were to make it again. Justify your recommendations.

Salad1 small chicken fillet

vegetable oil spray

2 spring onions, sliced

½ cup fresh bean shoots, brown tails removed

¼ red capsicum, thinly sliced

50 grams snow peas, julienned

½ carrot, thinly sliced diagonally

125 grams fresh Hokkien noodles

2 teaspoons fresh mint, chopped

2 teaspoons fresh coriander, chopped

Dressing¾ teaspoon sesame oil

1 teaspoon vegetable oil

½ lemon or lime, juiced

1 tablespoon kecap manis (Malaysian-style soy sauce)

2 tablespoons sweet chilli sauce

Chicken noodle salad


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Documents

4 Key foods of animal origin - Pearson