Chemistry Reference
In-Depth Information
Celluloseformsestersandethers,suchasnitrocellulose,celluloseacetate,andviscose,which
are products of great industrial importance. Only physically and chemically modiied cellulose
inds applications in various foodstuffs. For food products, methylcellulose ethers and carboxy-
methylcellulosepresenthighinterestsincetheycanbeappliedasthickenersandbinders(BeMiller
andWhistler1996).
2.5.1.3 Glycogen
Glycogen is a carbohydrate found only in animals. It can be thought of as the carbohydrate
reserve in animals in the same way as starch is the carbohydrate reserve in plants (Gaman and
Sherrington 1990). It is a glucose polymer and presents structural similarities with starch, but it
includesmorebranchesthanthat.Itisstoredmoreintheliverandlessinthemuscles.Glycogenis
awhite,amorphous,andtastelesspowdersolubleinwater.Itshowssimilarpropertieswithstarch
becauseofthesimilarityinstructure.Diluteacidshydrolyzeglycogentodextrin,maltose,andglu-
cose,whereasenzymeshydrolyzeittomaltose(Stick2001).
2.5.1.4 Other Homopolysaccharides
Inulin
: Inulin occurs as a reserve carbohydrate in many plant families such as scorzonera,
topinambur,chicory,rye,onion,anddahliabulb.Itcontainsabout30d-fructoseunitsinaβ-1,2-
linkage. This linear polysaccharide hasα-glucose residues in 2,1-bonding at its ends. Individual
α-glucose residues in 1,3-bonding have also been detected in the interior of the polysaccharide.
Inulin(molecularweight5000-6000)issolubleinwarmwaterandresistanttoalkali.Itisawhite
powder,solubleinhotwaterwithoutbeingcapableofforminggel,anditdoesnotgivecolorreac-
tionwithiodinesolution.Inulinisnondigestibleinthesmallintestine,butisdegradedbythebac-
teriainthelargeintestine.Itcanbeusedinmanyfoodsasasugarandfatsubstitute,forexample,
biscuits, yoghurt, desserts, and sweets. Inulin yields d-fructose on acid or enzymatic hydrolysis.
OligofructanshaveaslightlysweettasteduetothelowerDP(Belitzetal.2009).
Chitin
:Chitinisahomopolysaccharideinwhichthemacromoleculararrangementofthestruc-
tural units of glucose is similar to that of cellulose, except that in position 2 of the glucose, a
NHCOCH
3
groupisattachedasaligand.Itisthemaincomponentofthehardshellsofcrustaceans,
thusbeingresponsiblefortherigidityoftheshelltissue(Lee1975).
Mannans and galactans
:Mannansandgalactansarehomopolymersofmannoseandgalactose,
respectively. They are usually found together in food sources as galactomannans. They occur in
plantandanimaltissues.Theyareusedasthickenersandareproducedcommerciallyfromseeds.
Knowngalactomannans,ofgreatinterestforfoods,arecarrageenanandagar,whicharefoundin
plantgums(Meyer1987).
2.5.2 heteropolysaccharides
Thisgroupcoversasubstantialnumberofsubstancesmainlyofvegetableoriginwithcomplex
composition, some of which have interesting properties and, subsequently, useful applications in
foods.Themostimportantheteropolysaccharidesarehemicelluloseandpectincomponents.
2.5.2.1 Hemicellulose
Hemicellulose is a polysaccharide consisting mainly of d-xylose molecules joined withα-d-
(1→4)bonds.Itoccursinplantcellwallsalongwithotheringredients.Aftertheremovalofwoody
lignincomponents,anintimatemixturecalled“holocellulose”remains.Holocelluloseappearstobe
amixtureofcelluloseandothercompoundsthataresolubleinaqueousalkali.Thesealkali-soluble
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