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1、Unit1FoodQualityPartⅠView,ListenandSpeakTaskOne:FoodAdditives(1)Foodadditivesarewidelyusedinmanycountries.However,thediscoveryanumberofyearsagothatthefoodadditiveSudanRedwasharmfultohumanhealthledtoabacklashagainstallfoodadditives.Forexample,themilkwedrinkinthemorninghascalciumaddedtoit
2、;numerousbeveragescontaincalcium,magnesium,potassium,sodiumandotherminerals;storeboughtsaltcontainsiodine,zincandsilica;andpotatochipshaveasmanyas10typesoffoodadditives,suchasspices,ediblepigments,citricacid,flavoradditives,sweeteningagentsandsilica.MSGandcondimentsareconsideredfoodaddi
3、tives.Yeastpowderisalsoafoodadditivetooandisusuallyaddedtosteamedbreads.Evensodiumcarbonateisafoodadditive,too,andisoftenaddedtomakecongee.Tobetterunderstandthefunctionsoffoodadditives,Nature&Sciencedidtwointerestingexperimentsatabakery.Flour,eggs,sugar,saltandsodaarethebasicmaterialsus
4、edinbakingcakes.First,let’smakeacakewithoutanyadditives.Mixingeggyolksandwhitesevenly,wethenaddsomesugarintoit.Whentheeggandsugarare(done)beingmixed,weimmediatelyaddflour,water,sodaandbulkingagentsintothemixtureandrapidlymixthemtomakethebatter.Allthismustbedonewithin10to30secondsafterwh
5、ichthebattermustbeimmediatelyplacedintotheoventobake.Now,let’smakesomecakeswithadditives.Whentheeggsandsugararebeingmixed,weaddsomecakeoiltothemixture.Thecakeoiliscomposedofacidityregulators,antioxidants,vitaminCandsodiumbicarbonate.Itcanmaketheegg-sugarmixturerapidlyinflate.Afterflour,
6、waterandsodaarepouredintotheegg-sugarmixture,thecakeoilcanformcompoundmembraneswithproteinsinthecakebatter.Thiscansignificantlyimprovethestrengthandstabilityofbubblesinthebatterandmakesurethatalloftheingredientsareevenlydistributed.Evenafterthebatterisleftforsometime,thebubbleswillnotdi
7、sappear.Afterthecakesaretakenoutoftheovenwecanseethatthecakesthathadtheoiladdedtothemaremuchnicertolookatandaremoreflexiblethanthosewithouttheadditives.Eventheinsidesofthecakesareremarkablydifferent.Theinternalstructureofthecakewithoutadditivesisunevenandbrittle.Buttheinternals