Chemistry and Functional Properties of Carbohydrates and Sugars (Monosaccharides, Disaccharides, and Polysaccharides) - Sweeteners: Nutritional Aspects, Applications, and Production Technology - page 39

Texture : The dense solutions of carbohydrates that present high viscosities while interacting
with other food components contribute to texture enhancement (increasing viscosity, thickening,
adhesion).Also,carbohydratesinteractwithotherfoodingredientssuchasminerals,proteins,and
fatsthatcontributetotexture,offeringacryoprotectantroleinfrozenproducts.Somecarbohydrates
havefoundapplicationasfatsubstitutesbecauseoftherelativetexturethattheyoffertofoodsto
whichtheyareadded(BeMillerandWhistler1996).
2.7 QUaNtIFICatION OF SUGarS aND CarBOhYDrateS
Theidentiicationandquantiicationofmonosaccharides(reducingsugars)arebasedontheir
reducingproperties.TheFehlingsolution,whichcontainsCuSO 4 inalkalinesolution,isreduced
bysugarstoCu 2 Othroughwhichtheamountofsugarsisestimated.Becauseproteinscancause
interferencesduringanalysis,theyshouldthereforeberemovedbeforeanalysis.Fordisaccharide
orpolysaccharidequantiication,hydrolysismustprecede,andthenidentiicationoftheresulting
simplesugarsfollows(Belitzetal.2009).
Thedetectionofstarchisbasedonthecolorreactionbetweenstarchandiodine.Thequanti-
icationofstarchisaccomplishedafterenzymatichydrolysisviaglycoamylaseoracidhydrolysis
andconversiontoglucose,whichisdeterminedasreducingsugar.Forthedeterminationofdietary
ibersthefoodsamplesaredefatted,thenheatedtogelatinizethestarchandthensubjectedtoenzy-
maticdigestionbyprotease,amylase,andamyloglucosidasetoremovethedigestiblecomponentsof
thefood.Atthispointthetotaldietaryiberscanbedistinguishedintothosebeingsolubleinwater
(pectin)andinsoluble(cellulose,hemicelluloses)viaprecipitationwithethanol.Therespectiveresi-
duesarequantitatedandadjustedforproteinandash.
Thequantiicationofsugarsisalsoaccomplishedwiththeuseofenzymes,withphotometric
methods(themostcommonphotometricmethodinvolvestheuseofdinitrosalicylic,DNS,acid),
whereastheanalysisofindividualsugarsisperformedbyhigh-performanceliquidchromatography
(MortandPierce1995).
2.8 ChaNGeS OF CarBOhYDrateS DUrING FOOD
prOCeSSING—BrOWNING Or MaILLarD reaCtIONS
The reducing sugars during thermal processing of foods react with proteins to form brown-
colored polymers (nonenzymatic browning). With heating in dry state, carbohydrates are being
caramelized. Browning or nonenzymatic reactions are complex reactions that occur during food
processingorlongstorage.
Dependingonthefoodtype,thereactionsaresometimesdesirable,suchasthedarkcolorand
thecharacteristicodor(“baked”odor),andothersarenotdesirable,suchasthelossofnutrients,
thereductionoffoodproteinvalue,and/ortheformationoftoxicproducts.Thebrowningreactions
exhibitantioxidantactivityagainstlinoleicacidonlyinsomecases(BeMillerandWhistler1996).
Thenonenzymaticbrowningreactionsincludeaseriesofconsecutivereactionsthathavebeen
investigatedformanyfoodproducts.Threegeneraltypesofbrowningreactionshavebeenidentiied:
1. Thereactionofaldehydesandketones(amongthem,thereducingsugarsglucose,galactose,malt-
ose,lactose,andfructose)withaminocompoundssuchasaminoacids,peptides,andproteins,reac-
tionsknownasMaillardreactions.Thesereactionsareindependentofthepresenceofoxygen.
2. Caramelization,thechangethatoccursinpolyhydroxycarbonylcompoundssuchasreducingsugars
andsugaracidswhentheyareheatedtohightemperaturesandwhichisalsoindependentofoxygen.
3. The oxidative change of polyphenols to dicarbonyl or polycarbonyl compounds and possibly the
oxidationofascorbicacid.Thismaybepartiallyorwhollyenzymatic(LevyandFugedi2006).