analysis of sugars - cfs.gov.hk · 10 current aoac lc methods 984.22 purity of lactose lactose...
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Analysis of Sugars
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Definition
Nutritional labelling of food products requireslisting of sugars content.
Sugars means 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
HOOH
OH
OH
HO
OHOHO OH
OH
Fructose Glucose
O
HOOH
OH
OH
Galactose
OHO
HO OH
OH
Mannose
OH
OH etc
OHO
HOHO
OH
SucroseHO
OHOHO
OH
OO
HOOH
OH
OH
O
HOOH
OHOH
O O
HOOH
OH
OHO
HOHO
OH
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
OHOHO OH
OH
Fructose Glucose
O
HOOH
OH
OH
Galactose
OH
OHO
HOHO
OH
SucroseHO
OHOHO
OH
OO
HOOH
OH
OH
O
HOOH
OHOH
O O
HOOH
OH
OHO
HOHO
OH
OH
O
Lactose Maltose
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Common mono- and di-saccharides
OHO
HOOH
OH
OH
HO
OHOHO OH
OH
Fructose Glucose
O
HOOH
OH
OH
Galactose
OH
OHO
HOHO
OH
SucroseHO
OHOHO
OH
OO
HOOH
OH
OH
O
HOOH
OHOH
O O
HOOH
OH
OHO
HOHO
OH
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
OHO
HOOH
OH
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 fluorescence emission.
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Sugar Analysis
LC Methods with:
Refractive Index DetectorEvaporative Light Scattering DetectorPulsed 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 食品中果糖、葡萄糖、蔗糖、麦芽糖、乳糖的测定 高效液相色谱法
Determination of fructose, glucose, sucrose, maltose, lactose in foods – high performance liquid chromatography
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Mono- and di-saccharides analysis
Amine column
Acetonitrile/water (80:20)
Refractive index detector
2 mL/min at 30 oC
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Mono- and di-saccharides analysis
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-saccharides analysis
Shodex column
Water
Refractive index detector
0.5 mL/min at 80 oC
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Mono- and di-saccharides analysis
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Analysis of reducing sugars
AOAC methods:
920.183 Sugars (Reducing) in Honey 920.190 Sugars (Reducing) in Maple
Products945.66 Total Reducing Sugarsetc.
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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 weight carbohydrate of animal diet).
NOT appropriate for testing general food!!
OHO
HOHO
OH
HO
OHOHO
OH
O
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Typical analysis
Sugars in sampleSugars in sample
Preparation/Clean upPreparation/Clean up
LCLC
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Mono- and di-saccharides analysis
Extract thesugars fromsample using amixture of ethanoland water
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Mono- and di-saccharides analysis
Centrifuge themixture after the extraction
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Mono- and di-saccharides analysis
Clean up the extract by SPE
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Mono- and di-saccharides analysis
Clean up the extract by SPE
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Mono- and di-saccharides analysis
Analyse theextract 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 “0”Sugars ≤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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