Transcript EGGS
EGGS PROPERTIES Coagulation properties – trap milk when heated to form custards Provide structure to foods Contribute to texture by influencing flavor, smoothness, moistness NUTRITIVE VALUE 75% Water 12% Protein 10% Fat 1% Carbohydrate 1% minerals LIPIDS Almost all in yolk Triglyceride- almost all of eggs fat (66%) Phospholipids – lecithin (28%) Cholesterol – change in diet decreases amount of cholesterol (5%) Lecithin – naturally occurring emulsifier Negligible in albumen PROTEINS OVALBUMIN Major protein in egg white – 54% of total solids Globular protein – easily denatured Contributes to structure of products OVOTRANSFERRIN 12% of egg white Complexes with iron and inhibits growth of bacteria dependent on iron Not easily denatured by physical agitation Very susceptible to denaturation by heat when not bound by iron OTHER PROTEINS Ovomucoid – 11% of white solids, resistant to heat denaturation, inhibits proteolytic enzyme trypsin Ovomucin – 3.5% of solids, foam stabilizer, involved in deterioration and thinning of egg white as it ages Lysozyme – 3.4%, hydrolyze polysaccharides in walls of certain bacteria OTHER PROTEINS Avidin – minute amounts Presence has nutritional significance In natural state, binds with biotin – biotin cannot be absorbed Heating inactivates Vitellin and Lipovitellinin – lipoproteins that function as emulsifying agents, surrounds yolk CARBOHYDRATES Very small Form of glucose, mannose, galactose Glucose and galactose react with proteins in Maillard reaction Produce undesirable brown discoloration in dried and cooked egg whites VITAMINS AND MINERALS Shell – mainly calcium Yolk – phosphorus, iodine, zinc, iron (not well absorbed) Riboflavin – primarily in white Yolk – Vitamin A (fat & carotenoid pigments) Vitamin D, folic acid, pantothenic acid and B12 PIGMENTS Yolk – orange, red, yellow pigments – carotenoid pigments, found in yellow corn, green grass, alfalfa Xanthophyll - comes from animal feed- not a precursor to vitamin A Colorless sac, vitelline membrane surrounds yolk CHALAZAE - white cord to hold yolk in place STRUCTURE - SHELL Semi-permeable Porous - CO2 and H2O losses Air cell - formed as two keratinlike membranes separate Antibacterial Color – breed of hen, no effect on nutritional quality AGING CHANGES Yolks enlarge, less viscous, flatten, no longer centered Whites - thinner Contents shrink - H20 losses pH changes from 7.6 9.6 - allows bacterial growth INSPECTION FDA and FSIS share responsibility for egg safety 1999 egg safety plan to eliminate eggs as source of Salmonella enteridis 2000 safe handling procedures on cartons GRADING Letter grades Nutritive value remains the same Shell - shape, texture, soundness, cleanliness Interior - white, yolk, air cell size Candling - view of shell and inside of egg INSPECTION 1970 Egg Products Inspection Act Established standards Inspects plants processing eggs Wholesome and unadulterated and truthfully labeled egg products Imported eggs must meet same requirements as domestic EGG SIZE Not a part of quality Size = weight per dozen Younger chickens lay smaller eggs 3 ounces per dozen between each class 1 egg = ~ 1/4 cup or 4 T PROCESSING AND PRESERVATION Mineral oil - same day laid, partially closes pores = less microorganism permeability egg holds more moisture retains more CO2 so resists pH PASTEURIZATION Destroys microorganisms Required of all commercial liquid, dry or frozen products Must maintain functional qualities Ultrapasteurization with aseptic packaging - 10 week shelf life, Salmonella, listeria, E.coli free Now pasteurized eggs in shell FREEZING Pasteurized prior to freezing Uncooked retain properties Cooked - syneresis when thawed Yolks become gelatinous or lumpy when thawed Retard gelatination by adding salt, or sugar or corn syrup DEHYDRATION Began in 1870s Whites - remove glucose before drying (to prevent Maillard reaction), whipping aid is added to help with foams Add sugar to egg white to aid in hydration Yolks - irreversible changes in lipoproteins STORAGE Cold temperatures High humidity Hard cooked eggs - 1 week Whites - 4 days Yolks - 1-2 days Whole eggs in cartons, will absorb odors PREPARATION PRINCIPLES Centers around ability of proteins to coagulate when heated Coagulation – protein molecules attract and hold large quantities of water around them Gel formation – Solid particles held suspended in a liquid Whites and yolks coagulate at different temperatures Whites at 144-1490F; yolks at 149-1590F HEAT Denatures, coagulates to form gel Egg white – transparent viscous masssoft, white, opaque gel Heat past 1580F white becomes tough, porous Excessively high temperatures egg white gel loses water, shrinks, toughens High temps yolks become crumbly in texture Heat too quickly coagulated proteins curdle AGITATION Denatures proteins Disrupts bonds and initially causes foaming As more air incorporated soft foam gets larger and stiffer because increased denaturation Denatured proteins eventually curdle separate into fluffy masses and become dry as liquid drains out ACID Lower coagulation temperature Too much proteins denature severely and gel curdles pH greater than 9 or lower than 5 hardness and cohesiveness greater Prolonged heating peptidzation of protein and thinning of mixture (pie fillings become thin and runny) SUGAR Elevates temperature for coagulation The more sugar the greater the heat needed for coagulation More tender coagulum SALT Lowers temperature for coagulation Curdling may result from stirring gel so add salt before heating STARCH Coagulation and gelatinization occur at different temperatures Bring starch mixture to maximum thickness before adding uncooked egg OTHER CONSIDERATIONS DILUTION - coagulation temperature elevated if egg mixture is diluted CONCENTRATION OF EGG – lowers coagulation temperature COOKING CHANGES Frying - coagulates protein, overheated pan overcoagulates egg tough Hard cook - more tender if done at simmering not boiling temperature Color - green with long and high heat exposure due to formation of ferrous sulfate Old eggs – ferrous sulfate may form due to increase in alkalinity FOAMS Created as whites are beaten to incorporate air Holds shape as protein coagulates around air cells Provides leavening - dry foam not as effective as soft Yolks contain fat - physically interferes with alignment of protein around air cells MERINGUES Sweetened foams Weeping - release of water from undercooked or undercoagulated whites Beading - overcooked or overcoagulated meringues FACTORS AFFECTING FOAMS TEMPERTURE - room temperature best, but microbial growth a problem pH - ACID - beginning of beating = less volume, more stability, should be added after eggs reached foamy stage and have large air cells; (cream of tartar) SALT - adds flavor, less volume, less stability, add after foamy stage FACTORS SUGAR - less volume, add gradually at soft peak stage, after large cell and denaturation have begun; competes for water FAT - Substantially less foaming, less volume; interfering agent LIQUID - Increases volume and tenderness of foam, increases chance of syneresis; decreases stability FUNCTIONS Binder – such as meat loaf, coatings, proteins coagulate binding food into cohesive mass Emulsifier – form stable emulsions, coat oil drops to prevent them from combining with each other Foaming, leavening agent – Air bubbles expand with heat and egg white film hardens FUNCTIONS CONTINUED Interfering agent – Prevent crystals from coming together and getting larger Clarifying agent – proteins coagulate and trap loose particles EGG SUBSTITUTES NO yolks 80% egg whites Corn oil, nonfat milk solids, calcium caseinate, soy protein isolate, soybean oil, and other substances NUTRITIVE VALUE Biological value = 100- all absorbed protein is retained in the body Protein digestibility-correct amino acid score = measure of protein quality which compares amino acid balance with needs of a preschooler and corrects for digestibility = 1 SAFETY Contents of freshly laid egg generally sterile Salmonella enteritidis - may be found inside Egg shell - surface high level of bacteria - may enter through pores FDA prohibits use of raw or lightly cooked eggs in food production or manufacturing facilities - must reach internal temperature of 1450F