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Analysis of Sugars
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Definition
Nutritional labelling of food products requireslisting of sugars content.
Sugarsmeans all mono-saccharides and
di-saccharides present in food*.
*Codex Guidelines on Nutrition Labelling, CAC/GL 2-1985
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Mono- and di-saccharides
OHO
HO OH OH
OH
HO
OHO
HO OH
OH
Fructose Glucose
O
HOOH
OH
OH
Galactose
OHO
HO OH
OH
Mannose
OH
OHetc
O
HOHO
HO
OH
Sucrose
HO
OHO
HO
OH
OO
HOOH
OH
OH
O
HOOH
OHOH
O O
HOOH
OH
OH
OHO
HOOH
OH
O
O
HOOH
OH
OH
O
HOOH
OH
OHO
Lactose Maltose
Cellobiose
etc
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Common mono- and di-saccharides
OHO
HOOH
OH
OH
HO
OHO
HO OH
OH
Fructose Glucose
O
HOOH
OH
OH
Galactose
OH
O
HOHOHO
OH
Sucrose
HO
OHO
HO
OH
OO
HOOH
OH
OH
O
HOOH
OHOH
O O
HOOH
OH
OH
OHO
HOOH
OH
O
Lactose Maltose
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Common mono- and di-saccharides
OHO
HOOH
OH
OH
HO
OHO
HO OH
OH
Fructose Glucose
O
HOOH
OH
OH
Galactose
OH
O
HOHOHO
OH
Sucrose
HO
OHO
HO
OH
OO
HOOH
OH
OH
O
HOOH
OHOH
O O
HOOH
OH
OH
OHO
HOOH
OH
O
Lactose Maltose
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Common sugars in foods
Mono-saccharides:
Fructose, glucose, galactose
Di-saccharides:
Lactose, maltose, sucrose
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Properties of sugars
O
HOHO
OHOH
OH Trimethylsilylchloride Methylsilyl
ether
Primary amineGlycosylamine
Ac2O
Acetate
(LC Analysis)
(GC Analysis)(LC Analysis)
(GC Analysis)
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Properties of sugars
Water soluble.
Low thermal stability.
Do not have properties of fluorescenceemission.
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Sugar Analysis
LC Methods with:
Refractive Index Detector
Evaporative Light Scattering Detector Pulsed Amperometric Detector
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Current AOAC LC Methods
LactosePurity of lactose984.22
Glucose, fructoseRaw cane sugar2000.17
Glucose, fructose, sucrose,
lactose
Cane & beet final
molassess
996.04
Glucose, fructose, sucrose,
maltose
Presweetened cereals982.14
Fructose, glucose, lactose,maltose, sucrose
Milk chocolate980.13
Fructose, glucose, sucroseHoney977.20
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Current GB LC Method
GB-T 22221-2008
Determination of fructose, glucose, sucrose,
maltose, lactose in foods high performance
liquid chromatography
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Mono- and di-saccharidesanalysis
Amine column
Acetonitrile/water (80:20)
Refractive index detector
2 mL/min at 30 oC
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Mono- and di-saccharidesanalysis
Amine column may not be able to resolve all
the peaks.
Alternative column may be used, e.g.,
Shodex sugar column.
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Mono- and di-saccharidesanalysis
Shodex column
Water
Refractive index detector
0.5 mL/min at 80 oC
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Mono- and di-saccharidesanalysis
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Analysis of reducing sugars
AOAC methods:
920.183 Sugars (Reducing) in Honey
920.190 Sugars (Reducing) in MapleProducts
945.66 Total Reducing Sugars
etc.
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Analysis of reducing sugars
Fehling solution is used in the methods
It relies on chemical reaction between the
sugars and the Fehling solution.
OHO
HOOH
OH
OH
OHHO
HOOH
O
OH
R H
OCuO
R OH
O
+ Cu2O
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Limitation of analyzing reducing sugar
The best-known and most significantnon-reducing sugar in foods is sucrose !
(The most important
low molecular weightcarbohydrate of animal diet).
NOT appropriate fortesting general food!!
OHO
HOHO
OH
HO
OHO
HO
OH
O
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Typical analysis
Sugars in
sample
Sugars in
samplePreparation/
Clean up
Preparation/
Clean upLCLC
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Mono- and di-saccharidesanalysis
Extract the
sugars from
sample using amixture of ethanol
and water
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Mono- and di-saccharidesanalysis
Centrifuge the
mixture after the
extraction
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Mono- and di-saccharidesanalysis
Clean up the
extract by SPE
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Mono- and di-saccharidesanalysis
Clean up the
extract by SPE
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Mono- and di-saccharidesanalysis
Analyse the
extract using LC
with refractiveindex detector
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Proficiency test
FAPAS
LGC
AOAC
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CRM
BCR
NIST
LGC
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Points to note
Sugar alcohols (polyols) are not sugars
Not all monosaccharides and disaccharides
are reducing sugars. Test method for reducing
sugar may not be suitable for the analysis
of sugars.
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Points to note
Definition of 0Sugars 0.5 g/100 g
Limit of detection of total sugars should
be less than or equal to 0.5 g/100 g.
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Thank You