Chemistry Reference
In-Depth Information
HO
O
HO
O
HO
O
HO
HO
HO
OH
OH
OH
OH
D
-Xylose
OH
L
-Arabinose
OH
D
-Ribose
Figure 2.10
Important pentoses in food application.
Hexoses
:Hexosesarethemostinterestinggroupofmonosaccharides,asthemostwidespread
innaturesugars(aldosesorketoses)belongstothiscategory.Theycanbefoundinnatureeither
freeorascomponentsofpolysaccharidesandglycosides.Hexoseshaveasweettaste,aresolublein
waterandethanol,andareinsolubleinethylether.Theycanreduce
theFehling'ssolution,andmost
ofthemarefermentable(BeMillerandWhistler1996;Izydorczyk2005).
Themostimportanthexosesarefromthealdohexoses(glucose,galactose,andmannose)and
fromtheketohexoses(fructoseandsorbose;Figure2.11).
d
-glucose
(grapesugar,dextrose):Alongwithfructose,d-glucoseisfoundinfruitjuicesand
inhoney,anditisalsoabloodcomponent.Glucoseisaprimarycomponentofvariousoligosac-
charides(suchassucrose,lactose,andmaltose),polysaccharides(suchasstarch,glycogen,andcel-
lulose),andglycosides.Glucoseisindustriallyproducedbyacidorenzymatichydrolysisofstarch
(potatoorcorn)andbyacidhydrolysisofcellulose.Itisafermentablesugarbothunderaerobicand
anaerobic(alcoholic)conditions(Stick2001;Collins2006;Brown2008).Fermentationprocesses
havemanyapplicationsinfoods,thatis,productionofethanolinwineandbeer.
d
-galactose
:Itisacomponentofsomeoligosaccharidessuchasmilksugar(lactose),rafinose,
andmanycomplexpolysaccharidesknownasgalactans.Itcanbeconvertedthroughoxidationto
mucicacid,whichisusedforthedetectionandidentiicationofgalactose(BeMillerandWhistler
1996;Belitzetal.2009).
d
-mannose
:Itisrarelyfoundinafreeformandmostlyboundinglycosidesandpolysaccha-
rides.Itcanbeproducedbyacidhydrolysisofpolysaccharidesknownasmannanes(BeMillerand
Whistler1996;Belitzetal.2009).
d
-fructose
(fruitsugar,levulose):Itisthemostimportantketohexose.d-fructoseisfoundina
freeforminfruitjuices,must,andhoneyalongwithglucose.Itisacomponentofsucrose,rafinose,
andinulin(fructan);fructoseisproducedonlybyhydrolysisofinulin,(deMan1999;Collins2006;
Brown2008).
HO
OH
HO
HO
OH
HO
HO
OH
HO
O
O
O
HO
HO
OH
OH
HO
OH
D
-Glucose
D
-Galactose
D
-Mannose
O
OH
HO
O
OH
HO
HO
HO
HO
OH
HO
OH
D
-Fructose
D
-Sorbose
Figure 2.11
Important hexoses in food application.
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