food biotechnology dr. kamal e. m. elkahlout food biochemistry 4 protein foods

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  • Slide 1
  • Food Biotechnology Dr. Kamal E. M. Elkahlout Food Biochemistry 4 Protein Foods
  • Slide 2
  • Eggs
  • Slide 3
  • A hen requires 24-26 hours to produce an egg. Thirty minutes later she starts all over again. If an egg is accidentally dropped on the floor, sprinkle it heavily with salt for easy clean up. Egg yolks are one of the few foods that naturally contain vitamin D. Yolk color depends on the diet of the hen. Natural yellow orange Substances such as marigold petals may be added to light-colored feeds to enhance colors.
  • Slide 4
  • Egg Functions 1. Flavor, color, nutrition 2. Emulsifying agent 3. Aids in thickening/structure 4. Binding/coating agent 5. Leavening agent 6. Interfering substance
  • Slide 5
  • Composition & Nutritional Value 1. One medium egg contains between 4-5 grams of fat 2. High cholesterol ~200 mg/egg 3. High in Complete Protein 4. Little to no CHO 5. High in vitamins & minerals Vitamins A,D,E,K, some B vitamins, selenium, iodine, zinc, iron, copper
  • Slide 6
  • Cross Section of an Egg
  • Slide 7
  • SHELL The first line of defence 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) SHELL MEMBRANES There are two membranes on the inside of the shell One membrane sticks to the shell and one surrounds the white (albumen) The second line of defense against bacteria Composed of thin layers of protein fibres
  • Slide 8
  • GERMINAL DISC Appears as a slight depression on the surface of the yolk The entry for the fertilization of the egg WHITE (ALBUMEN) Two layers: thin and thick albumen Mostly made of water, high quality protein and some minerals 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 CHALAZA A pair of spiral bands that anchor the yolk in the centre of the thick albumen
  • Slide 9
  • YOLK MEMBRANE (VITELLINE MEMBRANE) surrounds and holds the yolk the fresher the egg the stronger the membrane YOLK 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 colour ranges from light yellow to deep orange, depending on the Xanthophyll content of the ration fed to the hen. AIR CELL forms at the wide end of the egg as it cools after being laid the fresher the egg the smaller the air cell
  • Slide 10
  • Characteristics of Fresh/High Quality Eggs Yolk is high & firm above the white Small yolk diameter Yolk is centered in white High ratio of thick to thin white High standing thick white
  • Slide 11
  • Which is the Highest Quality Egg
  • Slide 12
  • Deterioration Changes in Eggs Enlargement of air cell due to loss of moisture spoils the appearance of an egg cooked in the shell. Quality loss of CO 2,permits the egg white to become more alkaline P H 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 flatens. The thinner white is no longer able to keep the yolk in the centre.
  • Slide 13
  • Egg Candling Measures quality or freshness without breaking Characteristics of older, low quality eggs: Larger air cell Yolk off center Speckled appearance
  • Slide 14
  • Sizes U.S. sizes are defined by the weight of a dozen eggs. (Not individual eggs. An egg in a carton of Extra Large eggs need not weigh at least 27/12 ounces, but the dozen must weigh at least 27 ounces.) Most recipes that call for eggs usually mean Large eggs. Size Weight of a dozen eggs Jumbo30 ounces Extra Large27 ounces Large24 ounces Medium21 ounces Small18 ounces Peewee15 ounces
  • Slide 15
  • Preparation of Eggs Dry Heat Fried Scrambled omelets Moist heat Boiled eggs Coddled eggs prepared in a cup Poached eggs A variety of custards Eggs that are prepared using the microwave
  • Slide 16
  • 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 Gelation
  • Slide 17
  • 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 60C yolk begins near 65C Coagulation temperature is influenced by pH of the dispersion Presence of salts How fast the temperature rises
  • Slide 18
  • Foam Formation Foams are used as angel food, sponge cakes, meringues,etc 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.
  • Slide 19
  • Volume & Stability Factors Sugar increases stability delays foam formation added at foamy or soft peak stage Acid increases stability doesnt delay foam formation Fat decreases foam Formation Temperature room temperature 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.
  • Slide 20
  • 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
  • Slide 21
  • 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
  • Slide 22
  • Milk and Milk Products
  • Slide 23
  • Milk Milk should contain 8.25% milk-solid-not-fat 3.25% milk fat Milk is... a true solution for salts, lactose, water-soluble vitamins milk is a colloidal dispersion for proteins and some Ca phosphate a dilute emulsion for fat globules
  • Slide 24
  • Milk pH of milk: 6.6 at 25 o C when heated, pH decreases, H + are liberated when Ca phosphate precipitates Freezing Point: slightly lower than water Lower surface tension than water due to presence of milk fat, protein, free fatty acids, & phospholipids: easy to foam Components of milk varies with the feed, breed, nutrition & the physiological condition of the cow
  • Slide 25
  • Nutritional Components of Milk Water: 87%, a w = 0.993 Proteins: caseins, whey proteins, enzymes Lipids: mainly triglycerides Carbohydrates: mainly lactose, also glucose, galactose, & other saccharides Salts (
  • Milk Proteins - Whey proteins Not precipitated by acid, but easily denatured by heat (>60C) Four Fractions: lactoglobulins (50%), lactalbumins (25%), serum albumin immunoglobulins rich in sulfur-containing amino acids
  • Slide 29
  • Milk Proteins - Whey proteins Use of whey protein products: Dried Whey: puddings, cakes, baked products Whey protein concentrates: binder in sausage (up to 3.5%) Ultra Filtered Skim Milk : coffee whiteners Cheese Whey: animal feed
  • Slide 30
  • Milk Proteins - Enzymes Most of the enzymes are inactivated by pasteurization alkaline phosphatase is an index of adequacy of pasteurization (phosphatase test) Lipase may cause hydrolytic rancidity in dairy products if it is not deactivated
  • Slide 31
  • Milk Lipids Triglycerides = 98% of total milk lipids Other lipids: phospholipids, free fatty acids, sterols, carotenoids, fat-soluble vitamins Distinctive dairy flavor due to short-chain saturated fatty acids (C4-C10) : butyric (C4:0), caproic (C6:0), caprylic (C8:0), capric acids (C10:0) Fat content in milk decreases as cow ages Fat in feed does not appreciably affect fat content of the milk
  • Slide 32
  • Milk Carbohydrates Mainly lactose (4.8%), small amount glucose Lactose is the source of lactic acid, formed by bacteria as milk sours As milk is coagulated, lactose is in the whey Problems associated with lactose lactose intolerance crystals from condensed milk or ice cream lumping and caking of dried milk during storage
  • Slide 33
  • Milk Carbohydrates Use of lactose browning dispersing agent topping & icing carrier for flavor color ingredients body & viscosity
  • Slide 34
  • Vitamins Riboflavin water-soluble, light sensitive light yellowish & greenish color Carotene fat-soluble, yellowish color of milkfat skim milk is fortified with retinyl palmitate to replace the carotene in milk fat Milk also provides thiamine & niacin Vitamin D is added to almost all milk
  • Slide 35
  • Minerals Rich in Ca and P trace elements: Fe, Mg, Mo, Ni, Zn
  • Slide 36
  • Pasteurization of milk Heating milk at a definite temp for a definite time to destroy pathogens but not all bacteria 62 o C for 30 min 70 o C for 15 sec to 100 o C for 0.01 sec (HTST) 138 o C for 2 sec (UHT) to inactivate enzymes (lipase), control rancid & oxidized flavor, and increase shelf life
  • Slide 37
  • Pasteurization of milk
  • Slide 38
  • Fermentation of Milk All fermented milk contains lactic acid Undesirable (spoiled products) Desirable (buttermilk, yogurt, cheese) streptococcus lactis initiates the process with lactobacilli spp. continuing the fermentation Increased thickness due to the association of casein micelles, often accompanied by -lactoglobulin.
  • Slide 39
  • Homogenization of Milk Forces milk through small openings and break up the fat globules. The fat globule membrane is disrupted as new surfaces are created Homogenized milk is whiter in color, more viscous, more bland in flavor, and foam easily. Less heat stable (curdle more readily), form softer curd
  • Slide 40
  • 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
  • Slide 41
  • Drying of Milk Dry milk products whole dry milk powder (WDM) nonfat dry milk (NFDM) dry butter milk dried whey dry cream malted milk powder
  • Slide 42
  • Evaporation & Canning of Milk Evaporated milk sterilized canned milk that has been concentrated to about half its original volume by evaporation under a partial vacuum. 25% total milk solids including >7.5% milk fat high temp canning may give cooked flavor (methyl sulfide) storage at high temp for long time may develop off- color (Maillard reaction)
  • Slide 43
  • Evaporation & Canning of Milk Sweetened condensed milk 15% sugar is added after concentration of whole milk through evaporation total CHO concentrations of approx. 56% which is sufficient to prevent spoilage by microorganisms
  • Slide 44
  • Milk Foams Milk can form gas-in-liquid foams because the milk proteins have low surface tension - easier to spread the liquid proteins into thin films low vapor pressure - reduces the evaporation In fluid milk, the protein concentration is too low to produce a foam with any stability Foams can be formed in evaporated milk or dried milk solids.
  • Slide 45
  • Effect of Heat on Milk Products Scorching Some of the whey proteins ( -lactoglobulin and - lactalbumin) denature and ppt to form a thin layer of protein on the bottom. This protein gradually undergos the Maillard reaction with lactose, leading to scorching. Scum formation denatured protein molecules join together evaporation of water from the surface (increasing the concentration of casein and salts)
  • Slide 46
  • Effect of Heat on Milk Products Casien is quite resistant to ppt when heat is applied, but severe heating can cause it to form a curd at pH 7.
  • Slide 47
  • MEAT & POULTRY
  • Slide 48
  • 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.
  • Slide 49
  • 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 fibres, fat and bones of meat. Fat is deposited in the connective tissue within the muscle and is known as marbling.
  • Slide 50
  • 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 hound Sometimes there is color change in meat-due to change in the pigment myoglobin Molecules of myoglobin contain the iron porphyrin as shown:
  • Slide 51
  • Resonance of the conjugated double bonds in the porphyrin ring gives rise to the color of meat pigments.
  • Slide 52
  • Myglobin like haemoglobin can unite temporarily & reversibly with oxygen In live animal, the myoglobin takes O 2 from haemoglobin.When the animal dies, O 2 supply is cut off. Hence unoxygenated myoglobin in fresh beef is purplish-red in color. Upon exposure to O 2, oxymyoglobin is formed which is a bright cherry red color At low levels of O 2,the myoglobin- O 2 complex dissociates,oxidising the Fe to ferric state resulting in brownish red metamyglobin
  • Slide 53
  • 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.
  • Slide 54
  • Storing Meat Meat is highly perishable-refrigeration at 4C 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 days 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
  • Slide 55
  • Cooking meat Destroys microorganisms that may have contaminated the surface of meat-should be heated to a temp of 70C or until juice from meat is clear- not pink in color Affects tenderness Changes color Alters water holding capacity Develops flavor and characteristic aroma
  • Slide 56
  • 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 frying Recommended for tender cuts of meat
  • Slide 57
  • 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 coagulate Braising (pot roasting &breading) and cooking in water are moist methods of cooking Tough cuts of meat are ideal for moist cooking
  • Slide 58
  • Storage of cooked meat Leftover cooked meat should be cooled promptly and refrigerated at 4C if they are to be used within 3-4 days Otherwise they should be frozen at-18C
  • Slide 59
  • Effects of cooking on pigments and color 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
  • Slide 60
  • Effect of cooking on meat protein and tenderness 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 fibres and firmness of tissue
  • Slide 61
  • Flavor-cooking decomposes one or more precursers in the lean meat to give the basic cooked meat taste Less tender cuts of meat have more extractives-more flavorful 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. Fat melts, causing browning on the surface and increase in flavour. Effect on nutritive value-retention of B vitamins when meat is cooked is good, however there is greater loss of thiamine
  • Slide 62
  • Poultry Includes meat obtained from ducks, geese, guineas, pigeons, turkeys and chickens
  • Slide 63
  • Market class of poultry Different classes of poultry are marketed on the basis of their age that influences tenderness& fat content & dictates the cooking methods. Birds