Eggs Eggs Eggs • Source of

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Eggs Eggs Eggs • Source of Powered By Docstoc
• Source of high quality protein
• Important ingredients in prepared foods.
• Act as emulsifiers in mayonnaise, cream puffs, cheese
  schouffle and shortened cakes.
• Function as a coating materials for foods, a thickening
  agent in soft pie filling.
• A gelling agent in custard and structural material in
  shortened cake.
• Whipped to a foam, egg serve as a means of
  incorporating air into meringues, divinity,candy,puffy
  omelets and sponge and angel cakes.

• the first line of defense against the entry of bacteria
• can be brown or white; nutritional value of the egg is the same
• composed mainly of calcium carbonate
• approximately 8,000 to 10,000 tiny pores allow moisture and
  gases in (O2) and out (CO2)

• there are two membranes on the inside of the shell
• one membrane sticks to the shell and one surrounds the white
• the second line of defense against bacteria
• composed of thin layers of protein fibers
• appears as a slight depression on the surface of the yolk
• the entry for the fertilization of the egg
• there are two layers: thin and thick albumen
• mostly made of water, high quality protein and some
• represents 2/3 of the egg's weight (without shell)
• when a fresh egg is broken, the thick albumen stands up
  firmly around the yolk
• a pair of spiral bands that anchor the yolk in the centre of
  the thick albumen
• the fresher the egg the more prominent the chalazas
• unnoticeable when the egg is cooked
• surrounds and holds the yolk
• the fresher the egg the stronger the membrane
• the egg's major source of vitamins and minerals,
  including protein and essential fatty acids
• represents 1/3 of the egg's weight (without shell)
• yolk color ranges from light yellow to deep orange,
  depending on the Xanthophyll content of the ration fed
  to the hen.
• forms at the wide end of the egg as it cools after being
• the fresher the egg the smaller the air cell
• White (Albumen)
• Albumen accounts for most of an egg's liquid weight, about 67%.
• It consists of four opalescent layers of alternately thick and thin
• The white of a freshly laid egg has a pH between 7.6 and 7.9 and an
  opalescent (cloudy) appearance due to the presence of carbon
• As the egg ages the CO2 escapes which increases the pH.
• Egg white also becomes thinner as an egg ages because its protein
  changes in character. That's why fresh eggs broken onto a plate sit
  up tall and firm while older ones tend to spread out.
• The albumen of older eggs is more transparent than that of fresher
• Fresh egg whites coagulate in the range 62° to 65°C, the
  temperatures decrease with increasing pH and hence age. This is
  why very fresh eggs require more time to cook than older eggs.
• Yolk
• The yolk (yellow portion) makes up about 33% of the liquid weight
  of the egg.
• It contains all of the fat in the egg and slightly less than half of the
• With the exception of riboflavin and niacin, the yolk contains a
  higher proportion of the egg's vitamins than the white.
• All of the egg's vitamins A, D and E are in the yolk.
• Egg yolks are one of the few foods naturally containing vitamin D.
• The yolk also contains more phosphorus, manganese, iron, iodine,
  copper, and calcium than the white, and it contains all of the zinc.
  The yolk of a large egg yields about 250 kJ of energy.
• Egg yolks have a pH of about 6.0 which stays relatively constant as
  the egg ages as there is no CO2 loss. Coagulation occurs in the range
  65° to 70°C.
                  Quality of eggs
• A freshly laid egg has a high proportion of thick white that
  resist spreading when the egg is broken from the shell.
• The yolk will be upstanding and remains centered in the
• Changes in an egg leading to a deterioration in quality may
  occur as soon as the egg is laid.
  Blood or "meat" spots are occasionally found on an egg
  yolk. These tiny red or red-brown spots are not harmful.
  They are caused by the rupture of a blood vessel during
  formation of the egg. Blood spots do not indicate a
  fertilized egg.
• .
           Deteriorative changes
• Enlargement of air cell due to loss of moisture spoils
  the appearance of an egg cooked in the shell.
• Quality – loss of CO2 ,permits the egg white to
  become more alkaline
• PH of egg white may increase from about 7.6 (freshly
  laid) to 9.0 -9.7 in few days.
• The white becomes thin and spreads when broken
• White eventually becomes yellow and even cloudy.
• The yolk flattens.
• The thinner white is no longer able to keep the yolk in
  the centre .
• Candling
• Candling is the only method of testing eggs for
  quality, internally and externally, without
  breaking them. It consists of inspecting an egg
  with a beam of light that makes the interior
  quality visible. A very simple form of candling
  is placing a candle in a dark room and
  positioning an egg in front of the flame and
  looking at the interior quality
                    Grades of eggs
• In order of decreasing quality,    Grades of eggs
  grades are AA, A, and B. All
  ungraded eggs sold to
  consumers must meet B
  standards. “Restricted eggs”
  do not meet B standards; their
  disposition is regulated to
  prevent them from reaching
  consumers, although two
  types of restricted eggs,
  checks (the shell is cracked but
  the membrane beneath is not
  broken), and dirties, may be
  sold to factories equipped to
  process them properly.
• U.S. sizes are defined by    Size
                                             Weight of a dozen
  the weight of a dozen                      eggs

  eggs. (Not individual        Jumbo         30 ounces
  eggs. An egg in a carton
  of Extra Large eggs need     Extra Large   27 ounces
  not weigh at least 27/12
  ounces, but the dozen        Large         24 ounces
  must weigh at least 27
  ounces.)                     Medium        21 ounces
• Most recipes that call for
  eggs usually mean Large      Small         18 ounces
                               Peewee        15 ounces
   Effects of heat on Eggs protein
• Eggs are useful in binding, thickening and
  gelling agents because they contain proteins
  that are denatured by heat leading to
  coagulation or gelation
• Coagulation – involves a random aggregation
  in which protein – protein integration
• Gelation – an orderly aggregation in which
  protein –solvent as well as protein to protein
  integration denotes
• Egg white changes from a viscous ,transparent sol
  to an opaque ,elastic solid .
• Egg yolk increases in thickness as it is heated
  becoming either a pasty or mealy solid depending
  on heat
• Coagulation Temperature
  – White begins near 600C
  – yolk begins near 650C
• Coagulation temperature is influenced by
  – pH of the dispersion
  – Presence of salts
  – How fast the temperature rises
               Foam Formation
• Foams are used as angel food, sponge
• When the bubbles of air are incorporated in egg white
  (colloidal dispersion of protein in water) with a wire
  whip or the blades of a beater, individual proteins
  contribute aspects of its film –forming potential.
• The presence of hydrophobic groups with an affinity
  for air and hydrophilic groups that are soluble in water
  are essential in lowering surface tension which enable
  the incorporation of air possible and denaturation of
  surface protein molecules by heat alter the native
  conformation and thus stabilize the foam.
       Factors affecting foaming
• Utensils used – size of the bowl, type of beater
  – the finer the wire the thinner the blade, the
  smaller the cells and the finer the foam.
• Temperature
• Presence of fat, salt or acid
• Time of adding sugar.
         Methods of cooking eggs
•   Cooked in the shell
•   Poached egg
•   Fried Egg
•   Scrambled egg
•   Custards Soft pie filling
     Problems with cooking Eggs
• Boiled egg if overcooked a green ring is
  formed around egg yolk-due to the presence
  of iron and sulfur. can also happen if there is
  too much iron in cooking water.-chill egg in
  cold water
• Cooking leads to the oxidation of cholesterol-
  increases risk of heart disease
                    Health issues
• Eggs have cholesterol-increases risk of heart diseases
• Contamination by salmonella a pathogenic bacteria-hence
  commercially eggs should be washed with a sanitizing
  solution after being laid
• Cook eggs to kill pathogenic bacteria
• Food allergy esp in infants due to egg albumin hence
  introduction of egg white to infants is not recommended
• Raw egg whites contain a protein called conalbumin that
  binds iron as well as avidin that binds biotin &can impair
  function of other B vitamins
1.    How can you test the quality of an egg without breaking it? Describe
2.     How does heat affect egg protein?
3.     Compare fresh egg with a stale egg
4.     Why is the pH of egg yolk relatively stable?
5.    Why does the air cell enlarge?
6.    Which eggs cook fast? Give a reason
7.     Egg are a source of high quality protein. What do you understand from
      ‘high quality protein’?
8.     Give some functions of egg
9.     How can you from ‘foam’ from eggs?
10.    Why do we need to cook the eggs?
11.    What are some of the health issues associated with eggs?
12.    How are you going to prevent them?
13.    What are some of the problems of cooking eggs?
Plant proteins
                     Plant proteins
• Not much attention has been done on plant proteins then
  animal proteins.

• Plant proteins can be obtained from leaves,cereals,oilseeds
  and nuts. leaf proteins denature at 500C and undergo surface
  denaturation at pH 4.5-6.0.

• Wheat contains about 8-14% protein, rye -12%,barley -10%
  and rice -9%.
             Nutritional quality of vegetable proteins

• Vegetable proteins are of lower quality because they lack one or
  more of the essential amino acids, either in quantity or in
  unfavorable ratios

• The amino acid lacking is called a limiting amino acid

• Wheat is most limited in lysine, corn in tryptophan, and soybean in

• Legumes are low in Cysteine and methionine.
• Plant food are generally lower in fat, saturated fat and cholesterol
  and moderate in calories and protein

• The quantities of folic acid, magnesium, fibre, antioxidants (vit. E, vit.
  A, and carotenoids are higher in plant foods

• Having vegetarian diets lowers the risk of coronary diseases such as
  coronary heart disease,, diabetes.
• Plant foods are bulky hence people with high calorie demands for
  example small children may not be able to get enough calories from
  plant foods.
• Adequate amounts of vitamin D may be lacking in vegan diets if
  vitamin D fortified dairy foods are excluded. esp for young children
  and pregnant women
• VitaminB12 is only present in animal foods
• High content of plant foods increases amount of fibre, phytates and
  oxalates which binds to minerals in the intestine and limits their
  absorption leading to problems in calcium, iron and zinc absorption
                  Wheat Protein
• Wheat protein are unique among plant proteins
  and responsible for the bread making properties
  of wheat.
• There are 4 main fractions of proteins in wheat.
  1.   Albumin-water soluble and coagulated by heat
  2.   Globulin-soluble in neutral salt solution
  3.   Gliadin – a protein soluble in 70% ethanol
  4.   Glutenin – a glutelin insoluble in alcohol but slightly
       soluble in dilute acid or alkali.
• Gliadin and glutenin are the storage, or gluten
  forming, proteins of wheat. The formation of
  gluten takes place when flour is mixed with water.
• The gluten is a coherent elastic mass, which holds
  together other bread components such as starch
  and gas bubbles, thus providing the basis for the
  crumb structure of bread.
• Gluten proteins have a high content of glutamine
  but are low in the essential amino
  acids(lysine,methionine and tryptophan).
• The insolubility of gluten proteins can be directly
  related to their amino acids composition.
               Soybean Proteins
• Soya protein is a good source of all essential amino
  acids except methionine and tryptophan.
• The high lysine content makes it good complement to
  cereal proteins, which are low in lysine.
• Soya proteins have neither gliadine or glutenin, the
  unique proteins if wheat gluten. As a result, soya flour
  cannot be incorporated into bread without the use of
  special additives that improve loaf volume.
• The soya proteins have a relatively high solubility in
  water or dilute salt solutions at pH values below or
  above the isoelectric point. This means they are
  classified as globulins.
1. Why are vegetable proteins considered to be
   of lesser quality than animal proteins?
2. What are the advantages and disadvantages
   of vegetarianism?
3. How may an adequate diet be planned if
   only vegetable proteins are available?
            Sea food Proteins
• Excellent source of proteins
• Different forms of protein sources in sea
  – Fish
  – Shell fish
  – Crustaceans e.g
  – Mollusks e.g. bivalves –
• Composition of fish varies:
-low fat fish- eg cod, rockfish contain less than 2.5% fat

-medium fat fish-contain 2.5-5% fat eg yellow fin tuna, mullet swordfish,
  and bluefish

-high fat fish-contain more than 5% fat eg salmon, mackerel, albacore
   tuna, blue fin tuna, sardines, herrings, anchovies, trout.

Fat content of fish varies with its location and color of muscle. Red
   muscle in the belly flap area has maximum amount of oil followed by
   the flesh near the head. Sections from the white muscle tail is low in
   fat content.
• The protein content of fish is approximately 15-20%
• Two types of muscle in vertebrate fish
• Lateral muscle make up bulk of edible part, which is usually colorless
  except for salmon which is pink due to carotenoid - astaxanthin.
• Outside the lateral muscle is a small superficial muscle that fans out
  on each side of lateral line. It is dark reddish brown, rich in
• The muscle of fish consist of muscle fibers and connective tissues.
  Mycofibrils are embedded in the sarcoplasm of the fibers defined by
  the sacrolemma.
• Myofibrils appear to be made up of overlapping thick (myosin) and
  thin (actin) filaments.
• The contractile proteins – actin and myosin make up of about 2/3 of
  total protein in muscle.
• The connective tissue is more abundant in the skin, fins and skeleton
  than muscle.
                             Nutritive value
• The protein of fish is of excellent quality

• Fish contains both saturated and unsaturated fat, however the total
  fat content of raw fish is less than that of raw meat and poultry.

• Fish contains special fatty acids called omega 3 fatty acids which is
  associated with decreased incidence of heart disease.

• Fatty fish contain omega 3 fatty acid in highest concentrations.

• Shrimps are higher in cholesterol than other seafood, meat or
  chicken but are low in fat.

• Low in carbohydrate
• Vitamin content of fish varies according to the fat content. High fat
  fish are good sources of vitamin A and D
• Most fish are good sources of thiamin, riboflavin, niacin vitamins B6
  and B12
• However raw fish contains an enzyme thiaminase which breaks
  thiamin thus it is not absorbed. Cooking denatures and deactivated
  this enzyme.
• Fish particularly shellfish are good sources of minerals
• Fish canned with bones are good sources of calcium and
• Ocean fish are good source of iodine
• Oysters and clams are good sources of iron, zinc and copper.
• Tuna is a good source of selenium which protects against mercury
  and cadmium toxicity.
• However there is very little salt in the flesh of fish except shark meat.
  The salt content of fish is slightly higher than meat.
                                  Postmortem changes
•   Fish muscle undergoes rigor mortis similar to meat tissue.

•   The limp tissue becomes rigid and with time the muscle relax again

•   Time required for rigor mortis depends on the species, physical condition and temperature.

•   Poor physical condition depletes muscle glycogen eg if fish struggled before death,
    spawning, stress. High amount of glycogen will keep the fish in rigor longer- good quality

•   Cooling the fish quickly to 0° will delay the onset of rigor.

•   If fish undergoes rigor at high temp. and the concentration of glycogen is high then gaping
    can occur. Gaping results from tears in the connective tissue due to strong muscle
    contraction during rigor.

•   Fish should be filleted after rigor mortis has ended. If filleted before rigor-muscle will
    shorten and toughen later. If frozen pre rigor the fillets will go into rigor and slowly relax
    during freezing. If cooked before the muscle relax, it will become tough and distorted when
                                Fishy Odor
• Fishy odor is due to amines

• Amines are liquid at room temperature and not water soluble.

• Tirmethylamine oxide (TMO) is a natural amine found in fish muscle.

• As bacteria grow, they reduce this cpd to trimethylamine

• During cold /frozen storage TMO can be degraded to dimethylamine
  and formaldehyde.

• Bacteria also produce sulfur cpds and ammonia-unplesant odors.

• Lemon juice –improves the odor and flavor-amines to amine salts
                       Buying fish
• Eyes should be bright, clear and bulging

• Scales -should be shiny and clinging tightly to the

• Gills-reddish pink, surface free of dirt or slime

• Flesh-firm to the touch with no traces of browning
  or drying around the edges

• No fishy odor.
               Storage of fish
• Fish and shellfish are highly perishable,
  therefore icing or refrigeration is essential for
  highly – quality products.
• Spoilage occurs rapidly in fish and bacterial
  spoilage does not begin until the fish has gone
  into and passed out of rigor
• What happens to the fish when it is overcooked?
• What are the characteristics of fresh fish?
• Why does a fish spoil more quickly than other fresh
• What contributes to the fishy odor in fish and
  describe how this compound changes due to
  improper storage
• Which fatty acids are present in fish but not in meat?
  What is the importance of these fatty acids?
• Includes ducks ,geese,guineas,turkey and chicken.
• Different classes of poultry are marketed on the basis of age.
• Age influences tenderness and fat content and so dictates the
  cooking methods that are appropriate.
    –   Signs of youth
    –   Smooth leg skin
    –   Supple wing joint
    –   Pliable keel
    –   Breast bone
    –   Presence of pin feathers
    –   No air on the skin
    –   Little subcutaneous fat.
• The weight of the chicken varies with age.
     Preparing poultry for market
• Marketed ready to eat. i.e. heat, feet and entrails are
• Birds are fasted eight hours prior to slaughter.
• Killed by a method that minimizes struggle.
• Birds are scaled – dipped in hot water to remove feathers
• Evisceration follows scalding and picking.
• Chilling follows – prompt cooling is essential to control
  growth of bacteria .
• Trisodium phosphate solution as a spray or dip to follow
  chilling is an optional step to reduce but not eliminate
  bacterial contamination on the birds.
• Also important to control rigor mortis
• The time of onset of rigor, its duration and the
  tenderness of the meat once rigor has passed are
  influenced by the way the bird is cooled.
• To avoid meat toughness prompt cooling from
  body temperature to 150C before the pH is
  lowered to 6.3 by accumulation of lactic acid is
• Poultry goes in and out of rigor more rapidly then
  other meats.
• Aging longer then 24 hours results in no
  additional tenderizing.
            Inspection and grading
• All ready to eat poultry are inspected for quality
  and well as wholesome
• Characteristics in assigning grades
   –   Shape
   –   Meatiness
   –   Distribution of fat
   –   General appearance of the bird.
   –   Breaks in the skin, bruises and pin feathers lower the
• Quality grades for poultry are A,B,C.
Cuts of poultry
                    Handling raw poultry
• Should be held in the coldest part of a refrigerator and cooked within
   two or three days. Commercially it should be stored in the freezer.
• Incidence of Salmonella has been found to be high in raw poultry this
   is mostly due to cross contamination.
• If poultry is frozen it should be wrapped in moisture proof film to
   avoid freezer burn (when skin of chicken dries and discolors)
• Frozen poultry can be defrosted in two ways:
  -defrosted in the refrigerator
  -defrosted in cold water-water to be changed every 30 minutes
Defrosting at room temperature provides suitable conditions for
   bacterial multiplication.
       Nutritive value and composition
• Proteins supplied by poultry are complete proteins-
  contain all the amino acids that are essential for
  building body tissues.
• Good source of B vitamins-thiamin, riboflavin and
• Fat content in young birds is low. ducks and goose
  have more fat than chicken and turkey.
• Levels of iron and zinc are less than those of red
  meats-due to less myoglobin content of its muscle.
                 Cooking poultry
• Cooking method depends on the basis of tenderness. Young
  poultry can be cooked by broiling, frying, roasting
• Stuffing poultry before roasting-not recommended-stuffing
  raises temp. slowly –microorganisms (salmonella and
  staphylococcus) multiply.
• Microwaving –not recommended as heat is not distributed
  evenly. Pathogens such as Clostridium perfringens, salmonella
  and staphylococcus aureus survive microwave cooking
• Mature birds-moist methods allow time to tenderize meat
  such as stewing and braising.
• Poultry is cooked when its juice is free of pink color
               Cooking losses
• Cooking has little effect on vitamin B retention
-90% retention of riboflavin
-80% retention of thiamin
Leftover cooked poultry-cool promptly and
  refrigerate at 4°C if it is to be eaten within 2-3
  days. Otherwise it should be frozen and held
  at -18°C
                Frozen poultry
• Once thawed-do not refreeze
• When young chicken are cooked, discoloration in
  meat next to larger bone may occur- freezing and
  thawing release hemoglobin from the red cells in the
  bone marrow as the bones of young chicken is
  porous and heating denatures the pigment-
• Discoloration is not a problem in older birds-bones
  are dense.
       Flavor of cooked poultry
• Volatile carbonyls such as hydrogen sulfide-
  give cooked chicken its flavor
• Otherwise the sulfur compounds present will
  give only meaty of beef like aroma
•   Give reasons why poultry should not be thawed at room temperature.
•   How can you thaw poultry to avoid multiplication of microorganisms?
•   Why is the mineral content of poultry low?
•   What is the purpose of trisodium phosphate solution?
•   When grading a chicken what characteristics will you look at?
•   What is some common food borne illness spread due to improper
    handling of poultry? How can you prevent them?
•   What are some effects of cooking frozen poultry?
•   Does cooking poultry have any effect on its nutrient content? Explain
• Meat is the flesh of animals
• Composition
• Water content-Appro.75%
• About 15-20% protein mainly high quality
• Fat content ranges from 5-30%-varies with the type
  of animal with the breed, feed and age, pigs convert
  high % of their feed to fatty tissue
• Minerals eg Ca in bones, lean muscle rich in Fe and
  P.Liver excellent source of Fe and Vit.A
• Vitamins-excellent source of niacin and riboflavin.
  Pork rich in thiamin. meat is deficient in vit.C.
             Structure of meat
• Cut meat consists of lean tissue which is mainly
  protein with some bone and fatty tissue.
• lean meat consists of one or more muscle fibers that
  is the basic structural unit of meat.
• Connective tissue provides support for the muscle
  fibers, fat and bones of meat.
• Fat is deposited in the connective tissue within the
  muscle and is known as marbling.
Different levels of fat marbling in meat
                      Color of meat
• Fresh meat-color differences in
  color is due to the content of
  myoglobin concentration in meat
  (75%) remainder is due to
  haemoglobin(25%)beef has more
  myoglobin. Exercised muscles
  tend to be deeper red eg heel of
• Sometimes there is color change
  in meat-due to change in the
  pigment myoglobin
• Molecules of myoglobin contain
  the iron porphyrin as shown:
• Resonance of the conjugated double bonds in the
  porphyrin ring gives rise to the color of meat
• Myoglobin like hemoglobin can unite temporarily &
  reversibly with oxygen
• In live animal, the myoglobin takes O2 from
  haemoglobin.When the animal dies, O2 supply is cut
  off. Hence unoxygenated myoglobin in fresh beef is
  purplish-red in color.
• Upon exposure to O2,oxymyoglobin is formed which
  is a bright cherry red color
• At low levels of O2,the myoglobin- O2 complex
  dissociates ,oxidizing the Fe to ferric state resulting
  in brownish red metmyoglobin
                 Cured meat Pigments
• When meat eg. bacon, ham, corned beef is cured myoglobin unites with
  nitric oxide forming nitric oxide myoglobin giving it a light pink color
• When meat is exposed to low heat during curing, part of the nitric oxide
  myoglobin is changed to a stable complex (Fe still in ferrous state) The
  pigment is now called nitric oxide hemochrome
                    Storing Meat
• Meat is highly perishable-refrigeration at 4°C or lower reduces
   the growth of microorganisms on the cut surfaces and
   maintains freshness.
• Meat should be frozen if they are not to be used within three
• Raw meats carry pathogens-surfaces they contact should be
   washed thoroughly to prevent cross contamination
• Store :
ground meat & variety meat-no longer than 2days
Processed meats eg slices of ham, frankfurters & lunchen no
   longer than 5 days in refrigerator
Bacon smoked sausage and smoked ham up to 1 week
              Cooking meat
• Destroys microorganisms that may have
  contaminated the surface of meat-should be
  heated to a temp of 70°C or until juice from
  meat is clear-not pink in color
• Affects tenderness
• Changes color
• Alters water holding capacity
• Develops flavor and characteristic aroma
             Methods of cooking

• Meat can be cooked by either dry of moist methods
• Dry methods –meat is cooked added water and
  uncovered so that the moisture from the meat can
  evaporate. meat is in contact with hot air, a hot
  frying pan or hot fat from which heat is conducted
• Methods include-roasting, broiling, panboiling and
• Recommended for tender cuts of meat
• Moist cooking-meat is cooked in a covered utensil,
  water is added or meat is cooked in the
  steam/liquid released from the meat as the proteins

• Braising (pot roasting &breading) and cooking in
  water are moist methods of cooking

• Tough cuts of meat are ideal for moist cooking
        Storage of cooked meat
• Leftover cooked meat should be cooled
  promptly and refrigerated at 4°C if they are to
  be used within 3-4 days

• Otherwise they should be frozen at-18°C
   Effects of cooking on pigments and
• When meat is heated the myoglobin is first converted first to
  oxymyoglobin (bright red color)
• With further heating, protein moiety of the pigment is
  denatured, ferrous Fe is oxidized-meat color becomes grayish
  brown due to denatured globin hemichrome
 Effect of cooking on meat protein and
• Connective tissue-cooking decreases toughness of
  meat since the tensile strength of meat comes from
  fibres of collagen that are part of connective tissue
• Muscle fibres- proteins of muscle fibres are
  denatured but are not solubilized.
• They lose their ability to associate with water esp.
  with high temperatures
• This results in shrinkage of fibers and firmness of
• Flavor-cooking decomposes one or more precursors in the
  lean meat to give the basic cooked meat taste
  Less tender cuts of meat have more extractives-more
  Lactones and sulfur containing compounds eg sulfides,
  mercaptans and cyclic cpds such as pyrazine make
  important contributions to the flavor of cooked meats
• Initial fat content-meat cooked by pan frying and broiling
  differ little in fat content.
• Effect on nutritive value-retention of B vitamins when meat
  is cooked is good, however there is greater loss of thiamine
1. What gives the meat its color? Why does its color
   change upon exposure to oxygen?
2. Why does cured meat have a light pink color?
3. How can you prevent the growth of
   microorganisms in meat?
4. What is the effect of cooking on the pigments in
5. How does cooking affect meat quality? Meat
• Is the secretion of the mammary glands of
Milk fat
• is in the form of triglycerides, 95-95%
-66% saturated
-4% polyunsaturated
Milk has high no. of short chain fatty acids- butyric,
Remaining lipids are phospholipids(0.9-1%) and
  sterols(0.22-0.41%), minute quantities of free fatty
  acids and fat soluble vitamins (A,D.E and K)
• Carbohydrates-primary carbohydrate is lactose.(4.8%)
• Lactose is not very sweet as sucrose.
• In the souring of milk, lactic acid bacteria convert lactose to
  lactic acid eg in yoghurt and cheese production.
• Proteins-are found in two forms:
• Casein-predominant protein in milk (2.7% of total milk) is
  80% of the total proteins present in milk. It has all essential
  amino acids. They are separated from milk by acidification
  (pH 4.6)They form curd in milk.
• Whey- is 20% of the total proteins in milk. It has higher
  nutritional value than casein. Separated from milk by
  heat.It has the lactalbumin and lactaglobulin and they do
  not coagulate.
• Minerals-primary mineral in milk is calcium, phosphorous,
  potassium, chloride, and sulfur
                   Nutritive value
• Proteins in milk are of high quality-complete
• Lactose in milk promotes the growth of favorable
  microorganisms in the intestine that produce some
  B vitamins.
• Also lactose increases the absorption of the
  minerals calcium, phosphorous, magnesium and
• Iron and copper are found in low concentrations in
• Vitamins
• Whole milk is an excellent source of vitamin A but it
  does not provide large amount of vitamin D unless
• Milk is an excellent source of riboflavin, however
  when exposed to ultraviolet light, milk losses
  riboflavin quickly
• Thiamin and niacin are found in milk in fair
• Milk provides considerable amounts of tryptophan
  that is a precursor for niacin
• Small amount of ascorbic is present in raw milk.
                  Sanitary controls
• Purpose

• To insure a safe milk, free of disease producing
  bacteria, toxic substances and foreign flavors
• It also helps to produce milk that has low bacterial
  count, food flavor, satisfactory keeping qualities
  and high nutritive value.
• Pasteurization-the aim of pasteurization of milk is
  to get rid of any disease producing bacteria. Some
  nutrients are also destroyed eg, thiamin, vitamin
  B12,proteins and calcium.
• Extends storage life of milk.
• HTST(High Temperature Short Time) – heating milk
  to 72C for 15 seconds. The holding method is
  when milk is heated to 63C for 30 minutes.
• UHT(Ultra High Temperature) – treating milk at
  138C for 2 seconds and then cooling rapidly.
• LTLT-low temperature longer time.63° for 30
  minutes or more.
                     Kinds of milk
• Homogenization – the process of making a stable emulsion of
  milk fat and milk serum by mechanical treatment and
  rendering the mixture. Homogenized milk has a creamier
  structure, bland flavor and a whiter appearance

• Vitamin A/D fortified milk-milk that is fortified with vitamin A/D
• Skim milk-it contains less than less than 0.5% fat
• Low fat milk-has some of its fat removed.
• Flavored milk-milk can have a variety of flavoring agents-chocolate,
  strawberry, cocoa, coffee.
• Condensed milk is made by evaporating fresh milk sweetened with
  sucrose or dextrose to a point when it contains not less than 28%
  total milk solids and 8% milk fat
• Evaporated milk-is made by evaporating considerable amount of
  water so that the finished product contains no less than 7.5% by
  weight of milk fat and 25.5% of total milk solids.
• Dry milk-dried whole milk contains a maximum moisture content of
  5% and 26-39% milk fat. Non fat dry milk is made from pasteurized
  skim milk. It contains 5% moisture and 1.5% milk fat unless otherwise
• Is a product made from milk and S thermophilus and Lactobacillus
  bulgaricus bacteria
• Made from milk that is pasteurized or ultrapasteurised.
• The cooled milk is inoculated with a mixture of bacteria and
  incubated for several hours at 42-46°C
• During fermentation lactose is converted to lactic acid and the pH
• Some lactose is also converted to acetaldehyde that gives yogurt
• Diacetyl is produced from citrate that gives yogurt a buttery flavor
• Fermentation is stopped when yogurt has developed desired acidity
  and viscosity by chilling the containers or by heating.
• Flavors and stabilizers (gelatin and pectin) are then added .
1. What are the major constituents of milk?
2. Differentiate between casein and whey protein?
3. What is the lactose content in milk? what happens when
     lactose is attacked by lactic acid bacteria?
4. Define:
   –   Pasteurization
   –   Homogenization
5. Distinguish between UHT and HTST pasteurization?

6. What happens during the production of yogurt?
• Very hard ripened cheese-made form low fat cows milk. Low in
  moisture content. Has sharp flavor so minimum curing time is 6
  months eg parmesan cheese.

• Hard ripened cheese-made from pasteurized milk and subject to
  action of lactic acid bacteria which bring about the proper acidity of
  the mixture for curdling . eg cheddar, gouda, edam.

• Semisoft ripened cheese-have moderate moisture content-35-
  45%.They are manufactured in a similar manner as hard cheese but
  the curd may not be heated, cut eg blue veined cheese.

• Soft ripened cheese-eg cottage cheese, cream. They are made from
  cream, or from a mixture of milk, skim milk and concentrated skim
                    Nutritive value
• Good source of high quality protein
• Fat content depends on the type of cheese-cream
  cheese has more fat.
• Cheese made from whole milk are good sources of
  vitamin A and riboflavin. However it may contain
  high amounts of sodium as salt is used during
• Cheese made by acid coagulation retain only 25-
  50% of the original calcium content as calcium ion
  precipitates when curd is formed.
              Cheese manufacture
• Type of milk-homogenized milk is used for soft
  cheese because the breakdown of milk fat by mold
  enzymes is accelerated by increased surface area of
  the fat.
• It is not suitable for the production of hard cheese
  as it creates a brittle texture and is rubbery.
• White cheese is made from milk that is treated with
  0.002% benzoyl peroxide.
• Curd formation
• Formation of curd depends on the agent used for
  coagulation, the temperature of milk and the presence of
• Acid coagulated cheese is coagulated by lactic acid
  bacteria. This curd is soft and gel like. eg cottage cheese,
  cream cheese.
• Coagulation by enzyme rennin. This produces a tough
  rubbery curd with low moisture content eg cheddar cheese
• Enzyme coagulation-reduces the time required
• Temperature of milk during coagulation affects the texture
  and physical characteristics
• Presence of salts influences curd formation. Up to 0.02 %
  calcium chloride is added to milk to improve curd strength
  and accelerate coagulation
                    Curd treatment
• Once the curd is formed, it is:
• Cut-to increase surface area and permit loss of moisture,
  ensure uniformity in moisture, firmness and elasticity.
• Heated-to increase expulsion of whey, allow lactic acid
  development, reduce undesirable microorganisms, and
  produce firm rubbery body
• Whey is removed
• Salt is then added ranging from 1%(cottage) to
  5%(parmesan)This retards growth of microorganisms and
  lactic acid bacteria and improves flavor, texture and
• Finally curd is pressed to remove traces of whey, reduce the
  openness of curd and complete the manipulation.
                         Ripening and curing
• Ripening –when physical and chemical changes occur to the curd
   during curing
• Curing- is the methods and environmental conditions eg length of
   time, temperature, humidity and sanitation.
• Cheese may be ripened between 2-24°C
• During ripening:
-Proteins are hydrolyzed into proteoses and peptones and then into
   peptides and amino acids-softer cheese.
-Fats are hydrolyzed into acetate and volatile fatty acids that contribute
   to sharp flavor of aged cheese
- The carbohydrates in cheese are broken down into lactic acid which
   contributed flavor and increases its shelf life
Some cheese are inoculated with molds that change its character and
   flavor. Some of these may produce eyes in the cheese (holes)
            Care and storage
• Most cheese spoil quickly so they must be
  placed in a covered container and refrigerated
  until consumed.
• It is best to store cheese in its original
1. Why is cheese a good substitute for milk?
2. What contributes to increased shelf life of cheese?
3. What contributes to the sharp flavor of aged
4. What is the function of salt in the production of
5. Which cheese has less calcium?
6. What is the purpose of cutting the curd?
7. What is the purpose of heating the curd?

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