Analysis of Sugars(1)

8/11/2019 Analysis of Sugars(1)

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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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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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Shodex column

Water

Refractive index detector

0.5 mL/min at 80 oC


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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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Extract the

sugars from

sample using amixture of ethanol

and water


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Centrifuge the

mixture after the

extraction


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Clean up the

extract by SPE


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Clean up the

extract by SPE


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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

Analysis of Sugars(1)

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