应用化学专业英语lesson19introductiontofoodchemistry

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1、Lesson19IntroductiontoFoodChemistryWhatisinfood?Howcanchemistrybeusedtounderstandfoodandcooking?Howiscookingchemistry?Thereactionsthattakeplacewhenfoodiscookedmakeiteasiertodigest.Cookingisatypeofchemistry.Duringcooking,irreversiblechemicalreactionsoccurand

2、newproductsareformed.Otherchemicalreactionscanspoilfoodandmakeitunsafetoeat.areexposedtotheair.Cookingalsokillsmicrobesthatcanbefoundinfood.ApplesreactwithoxygenandturnbrownwhentheyWhatmoleculesarefoodsmadeof?Therearethreemaintypesoffoodmolecules.Proteinsar

3、echainsofdifferentaminoacids.Fatsaremadeupoflipids.Alipidhasastructureofthreefattyacidmoleculesandaglycerolmolecule.Carbohydratesarechainsofrepeatingmoleculesofglucoseandothersugars.Foodalsocontainsvitaminsandminerals,whichareneededinsmallamountsforahealthy

4、body.Whydoeggslookdifferentcooked?Changingtheshapeoftheproteinalsochangesitsproperties.Theproteinbecomeseasiertodigestandmoreusefultothecellsofthehumanbody.Eggsareaproteinfoodandsoaremadeupofaminoacidchains.Wheneggsarecookedtheybecomefirmer.Thisisbecausecoo

5、kingeggschangestheshapeoftheaminoacidchains.Thisiscalleddenaturing.Meatisalsomadeupofaminoacidsandreactstocookinginasimilarway.Whathappenswhendriedpastaiscooked?Pastaismadeupofstarchgranules.Whenitiscookedinboilingwater,thestarchgranulesabsorbwaterandthepas

6、tabecomessoftandedible.Itisnowrehydrated.Freshly-madepastacontainswater,whichcanmakeitgooff,andsoitmustbeeatensoonafteritismade.Milk,fruit,vegetables,meat,soupsandsaucescanallbedehydratedtostopthemfromspoiling.Topreservepasta,thewatercontentisremovedbyleavi

7、ngitinahotenvironment.Itbecomesdehydrated.preservativesandantioxidantsemulsifiersandstabilizersWhatareadditives?Traditionally,herbsandspiceshavebeenaddedtofoodtoimproveitsflavour.Lemonjuice(citricacid),saltandvinegarhavealsobeenusedtohelpfoodlastlonger.Toda

8、y,awiderangeofnaturalandartificialingredientsareusedinsmallquantitiestoenhanceorpreservefood.Thesearecalledadditives.Themaingroupsofadditivesare:flavouringscolourings.TypesofadditivesTypesofadditives–a