Analysis of Sugars
1 Definition
Nutritional labelling of food products requires listing of sugars content.
Sugars means all mono-saccharides and di-saccharides present in food*.
*Codex Guidelines on Nutrition Labelling, CAC/GL 2-1985
2 Mono- and di-saccharides
HO OH OH OH OH OH OH O OH O O O etc HO HO OH HO OH HO OH HO OH HO OH OH
Fructose Glucose Galactose Mannose
OH
O OH HO OH OH HO OH O HO HO OH O O HO HO O OH HO O O O OH HO OH OH OH O HO OH OH
OH OH
O O HO O etc HO HO OH OH OH Cellobiose
3 Common mono- and di-saccharides
HO OH OH OH OH O OH O O HO OH HO OH HO OH HO OH OH Fructose Glucose Galactose
OH
O OH HO OH OH HO OH O HO HO OH O O HO HO O OH HO O O O OH HO OH OH OH O HO OH OH HO OH Sucrose Lactose Maltose
4 Common mono- and di-saccharides
HO OH OH OH OH O OH O O HO OH HO OH HO OH HO OH OH Fructose Glucose Galactose
OH
O OH HO OH OH HO OH O HO HO OH O O HO HO O OH HO O O O OH HO OH OH OH O HO OH OH HO OH Sucrose Lactose Maltose
5 Common sugars in foods
Mono-saccharides:
Fructose, glucose, galactose
Di-saccharides:
Lactose, maltose, sucrose
6 Properties of sugars
(LC Analysis)
OH Trimethylsilyl Primary amine chloride Glycosylamine O Methylsilyl HO ether (LC Analysis) HO OH (GC Analysis) OH
Ac2O
Acetate (GC Analysis)
7 Properties of sugars
Water soluble.
Low thermal stability.
Do not have properties of fluorescence emission.
8 Sugar Analysis
LC Methods with:
Refractive Index Detector Evaporative Light Scattering Detector Pulsed Amperometric Detector
9 Current AOAC LC Methods
977.20 Honey Fructose, glucose, sucrose
980.13 Milk chocolate Fructose, glucose, lactose, maltose, sucrose 982.14 Presweetened cereals Glucose, fructose, sucrose, maltose
984.22 Purity of lactose Lactose
996.04 Cane & beet final Glucose, fructose, sucrose, molassess lactose 2000.17 Raw cane sugar Glucose, fructose
10 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
11 Mono- and di-saccharides analysis
Amine column Acetonitrile/water (80:20) Refractive index detector 2 mL/min at 30 oC
12 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.
13 Mono- and di-saccharides analysis
Shodex column Water Refractive index detector 0.5 mL/min at 80 oC
14 Mono- and di-saccharides analysis
15 Analysis of reducing sugars
AOAC methods:
920.183 Sugars (Reducing) in Honey 920.190 Sugars (Reducing) in Maple Products 945.66 Total Reducing Sugars etc.
16 Analysis of reducing sugars
Fehling solution is used in the methods
It relies on chemical reaction between the sugars and the Fehling solution.
O O CuO +Cu2O R H R OH
OH OH
O OH HO HO HO OH HO O OH OH
17 Limitation of analyzing reducing sugar
The best-known and most significant non-reducing sugar in foods is sucrose!
(The most important OH
O low molecular weight HO HO carbohydrate of animal diet). HO HO O O OH NOT appropriate for testing general food!! HO OH
18 Typical analysis
SugarsSugars inin Preparation/Preparation/ LCLC samplesample CleanClean upup
19 Mono- and di-saccharides analysis
Extract the sugars from sample using a mixture of ethanol and water
20 Mono- and di-saccharides analysis
Centrifuge the mixture after the extraction
21 Mono- and di-saccharides analysis
Clean up the extract by SPE
22 Mono- and di-saccharides analysis
Clean up the extract by SPE
23 Mono- and di-saccharides analysis
Analyse the extract using LC with refractive index detector
24 Proficiency test
FAPAS
LGC
AOAC
25 CRM
BCR
NIST
LGC
26 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.
27 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.
28 Thank You
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