Chemistry Reference
In-Depth Information
8.9.3 Creaming
Incakesandcookies,sugarandsweetenerspromotelightnessbyincorporatingairintheform
ofsmallaircellsintotheshorteningduringmixing.Duringbaking,theseaircellsexpandwhen
illedwithgasesfromtheleaveningagents(Ponte1990).
8.9.4 egg Foams
Sugarservesasawhippingagentforthestabilizationofeggfoams.Infoam-typecakes,sugars
interactwitheggproteinstostabilizethewhippedfoamstructure,makingitmoreelastic,soair
cellscanexpand(Ponte1990;Gates1981).
8.9.5 Gelatinization
During baking, sugar absorbs liquid and delays gelatinization. In cakes, the heat of baking
causesthestarchinlourtoabsorbliquidandswell.Thisiscalledgelatinization.Asmoreliquidis
absorbedbythestarch,thebattergoesfromaluidtoasolidstate,settingthecake.Sugarcompetes
withstarchforliquidandslowsgelatinization.Thetemperatureatwhichthecaketurnsfromluid
tosolidisattainedonlywhentheoptimumamountofgasesareproducedbyleaveningagents.
Thesamemechanismoccursinbreads.Abreadwithamoretendercrumbtextureresults(Ponte
1990;TheSugarAssociation1992).
Starchgelatinizationisaphysicochemicalphenomenoninvolvingthedisaggregationofstarchgran-
uleswithinanaqueousenvironmentatasuitabletemperature.At50°C-70°C,dependingonthetypeof
starchanditsorigin,waterswellsthestarchgranules,andamoreorlesshomogeneousgelisformed.
Starch gelatinization has been studied by many researchers, who have advanced hypotheses
aboutthemolecularmechanismandstudiedtheinluenceofsomecomponents,suchaswater,lip-
ids,sugar,andsalts,onthephenomenon(Horton,Lauer,andWhite1990;WhiteandLauer1990;
SladeandLevine1991;LiuandLelievre1992).
Itshouldbenotedthatmostofthesestudieswerebasedontheapplicationofdifferentialscanning
calorimetry(DSC).DSCstudieshaveshownthatstarchgelatinizationappearsasasingleendothermic
peakstartingatabout60°Cathighmoisturelevels(>70%;Zanoni,Schiraldi,andSimonetta1995).
Zanoni,Schiraldi,andSimonettaconstructedanaivemodelofstarchgelatinizationkineticsto
determineacontrolparameterofthebakingprocess(i.e.,abakingindex).Breaddoughsamples
wereinstantaneouslyheatedatdifferenttemperatures(60°C-90°C)forvaryingtimesandthensub-
jectedtoDSCtoevaluatetheextentofstarchgelatinization.Calorimetrictraces,aftersmoothing
andstandardization,weredeconvolutedintooneortwoGaussiancurves,dependingonthetreat-
menttemperatureandtime.Thissuggeststhesystemisamixtureoftwocomponents,thesecondof
whichwasfoundtohavealowergelatinizationrate.
8.9.6 Caramelization
Sugarcaramelizeswhenitisheatedaboveitsmeltingpoint,addinglavorandleadingtosurface
browning,whichimprovesmoistureretentioninbakedproducts.Atapproximately175°C,melted
dry sugar takes on an amber color and develops an appealing lavor and aroma. Caramel is that
amorphoussubstanceresultingfromthebreakdownofsugar.Caramelizationtakesplacewhenheat
isappliedintheovenwhenbakingdoughcontainingsugarandrepresentsoneofthewaysinwhich
surfacebrowningoccurs.Thegolden-brown,lavorful,andslightlycrispsurfaceofbreads,cakes,
and cookies gives a good taste and helps retain moisture in the baked product, thus prolonging
freshness(Ponte1990).
Noneoftheknownalternativesweetenersparticipateincaramelization.
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