Chemistry and Functional Properties of Carbohydrates and Sugars (Monosaccharides, Disaccharides, and Polysaccharides) - Sweeteners: Nutritional Aspects, Applications, and Production Technology - page 36

arecapableofforminggels(gellies)withsugarandacidor,ifsuitablylowinmethoxylcontent,with
certainmetallicions.Thesaltsofpectinicacidareeithernormaloracidpectinates.
4. Pectin :Thegeneralterm“pectin”(orpectins)designatesthosewater-solublepectinicacidsofvary-
ingmethylestercontentanddegreeofneutralization,whicharecapableofforminggelswithsugar
andacidundersuitableconditions.
5. Pectic acid :Theterm“pecticacid”isappliedtopecticsubstancesmostlycomposedofpolygalact-
uronicacidsandessentiallyfreefrommethylestergroups.Thesaltsofpecticacidareeithernormal
oracidpectates.
Pectins :Pectinisapolysaccharidefromterrestrialplants,whichfunctionsasanintercellular
cementandhelpstoholdplantcellstogether.Thetextureofnonwoodyvegetativeplantmaterial
suchasfruitsandtubersisdependentonthepectincontent.Commercialpectinisisolatedfromcit-
rusfruit(apples,lemons,limes)orapplerindobtainedfromfruitjuiceprocessing(Owusu-Apenten
2005).
Themainuseofpectinisingels'formationsandhighsugarcontentjams.Theseproductsare
producedfrompectinsinwhichatleast50%ofcarboxylgroupsareesteriiedwithmethylalcohol
(degreeofmethylation,DM=50).
Whenahotaqueousmixtureofsugar,acid,andpectinsiscooled,itsetsintoagel;severaltheo-
rieshavebeenproposedabouttheformationofthisgel.Thepecticsubstancesthatproduceirm
gelsarethosethathavelargemolecularweightwithahighDM(fewfree-radical-COOH).With
increasingDM,thetemperatureinwhichagelcanbeformedgetshigher.PectinswithlowDM
(manyfree-radical-COOH)formgelsbyjunctionoftheirmolecules(throughcarboxylgroups)with
divalentcations,especiallycalcium;theydonotrequiresugarstoformgelsandcangiveirmgels
onawiderangeofpH(Meyer1987).
Gel formation :Thegelformationdependsonmanyfactors:
1. Thepercentageofpectin(%):Asthepercentageofpectinincreasesinmixtures,theirmnessofthe
gelproducedincoolingincreasesthestabilityofthegel;usually1%percentageofpectinisused.
2. The molecular weight of pectic substances: with increasing molecular weight, the gelling power
increases.
3. Themethylestercontent(%):themorethemethylesters,theirmerthegel(inpractice,atleast8%
ofmethylestercontentisused,whichrepresentsesteriicationofhalfofthecarboxylgroups).
4. ThemostpH-irmgelsareformedasthepHdecreasesapproximatelyatavalueof3.2.Withvery
lowpHs,theamountofpectincanbedecreasedandasatisfactorygelisformed(usuallythereisan
optimumpHvalue;andifthepHisloweredbelowthispoint,theirmnessofthegeldiminishesand
excessivesyneresisdevelops).
5. Sugars(mainlysucrose)arenecessaryfortheformationofthepectingelsandmustbepresentina
minimumconcentration,usually65%.Thehighconcentrationofsucroseisthoughttostrengthen
hydrophobicinteractionsbetweenmethylatedpectinchains(Owusu-Apenten2005).
Gel characteristics :Thegelthatgivesapectinischaracterizedbythefollowing:
1. Thedegreeofgelation,whichevaluatestheabilityofapecticsubstancetoproducegel.Asitisdif-
iculttomeasurethedegreeofgelation,itisdeterminedbytheamountofsugarneededtoform“a
satisfactorygel.”
2. The setting time, which is the time that elapses between the addition of all components and the
formationofagel.Settingtimeevaluatesthequalityofpecticsubstancesincerapidsettingdoesnot
implyairmgel.
Commercialpectinsareavailableeitherasa“rapidset”or“slowset,”dependingontheapplica-
tion.Ahotmixtureformsagelduringcooling,andthesettingtimeofthegelisinluencedbysev-
eralfactorssuchasthepotshapeandsizeandthecoolingrate.A“rapidset”beginsatabout88°C,
whereasa“slowset”formsagelbelow54°C.ThepHofthemixturehasaninluenceonsetting