Chemistry and Functional Properties of Carbohydrates and Sugars (Monosaccharides, Disaccharides, and Polysaccharides) - Sweeteners: Nutritional Aspects, Applications, and Production Technology - page 20

HO OH HO

HO OH HO HO OH

HO HO HO

OH

HO OH HO OH OH

Xylitol

D -Sorbitol

D -Mannitol

Figure 2.12 Important sugar alcohols in food application.

2.3.4 Derivatives of Monosaccharides

Sugar alcohols : They are polyols (or polyalcohols) that are produced by reduction of sugars
(deMan 1999; Duyff 2006). The most important polyols for foods are hexitols (d-sorbitol and
d-mannitol)andpentitol(xylitol;Figure2.12).
d -sorbitol (glucitol) :Itisthemostwidespreadinnaturepolyol.Freshfruitscontain5%-10%sor-
bitol,whereasgrapescontainlittleornone.SorbitolcannotreduceFehling'ssolution,anditisnotfer-
mentedbyyeasts.Itisindustriallyproducedbycatalyticreductionofrespectivehexoses.Sorbitolis
hygroscopic,andthus,itisusedinconfectioneryproductstocontributetofreshnessandsofttexture.
Becauseofitssweettaste,itisalsoused(inlimitedamounts)asanalternativetosucrosesweetener
fordiabetics.Thewell-knownfoodemulsiiersTWEEN(polyoxyethylenesorbitanesters)andSPAN
(sorbitanestersoffattyacids)arealsoproducedfromsorbitol(Coultate2002;Collins2006).
Xylitol :Xylitolisproducedbycatalytichydrogenationofxylose.Itisapentitolthathassweettaste
andcaloricvalueequivalenttosucrose.Xylitolcanalsobeusedasanalternativetosucrosesweetenerfor
diabeticsbecauseitsmetabolismincontrolledamountsisindependentofinsulin(Collins2006).
Uronic acids : They are derived from the corresponding aldoses by protecting the aldehyde
groupandoxidationoftheterminalCH 2 OHgrouptoCOOHasmentionedabove.Uronicacidsare
notfoundinnatureinafreeform;however,theyhaveanimportantroleinthesynthesisofsome
glycosidesandpolysaccharidessuchaspectins,alginicacids,andnatural(plant)gums.Themost
commonuronicacidsared-galacturonicandd-mannuronicacid(BeMillerandWhistler1996).
Glycosides : In glycosides, a reducing sugar component (glycone) is bound to a noncarbohy-
drate moiety (aglycone) such as steroids and lavonoids by acetal hydroxyl (glycosidic linkage).
Glucosides can be decomposed back to the primary components through acid hydrolysis. They
do not show mutarotation and cannot reduce the Fehling's solution. The most common sugar in
glycosides is glucose (from which their name derives), whereas the noncarbohydrate ingredient
maybeasubstanceorgroupcontainingN,S,andOresultinginN-glycosides,S-glycosides,and
O-glycosides,respectively.Glycosidesarewidespreadinnature,commonlyinplants.Characteristic
glycosidesareanthocyanin(O-glycoside,anaturalpigment),sinigrin(S-glycoside,responsiblefor
thepungenttasteofmustard),andgossypol(toxicpolyphenolicconstituentofcotton;deMan1999).

2.4 OLIGOSaCCharIDeS

Oligosaccharidesaresaccharidepolymerscontainingtwoto10monosaccharidesjoinedbygly-
cosidicbondsthroughremovingwatermolecules.

2.4.1 Disaccharides

Disaccharidesareclassiiedintotwocategoriesaccordingtothewaythatthetwosimplesugars
arejoined:

1. Trehaloseorsucrosetype,inwhichthehemiacetalhydroxylgroupsofthetwomonosaccharidesare
engagedintheglycosidicbond,sothereisnofreehemiacetalunit.Thus,thesedisaccharidescannot