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220_002 #04

FOOD & BEVERAGE A P P L I C AT I O N N O T E
Page : 1

CARBOHYDRATES IN FOOD

THE FINEST LC-EC APPLICATIONS FOR FOOD & BEVERAGE ANALYSIS EVER PROCESSED

INTRODUCTION Carbohydrates not only provide the most easily accessible energy source for our body, they also play an important role in many physiological processes. They are involved in intercellular recognition, infection processes, and certain types of cancer. Carbohydrates analysis is of interest to the food industry but also many fields in life sciences. Analytes of interest include simple mono- or disaccharides (such as glucose and sucrose), oligosaccharides (Maltodextrin), polysaccharides (starch, cellulose) and glycoproteins.

• • • •

Carbohydrates in food & life sciences Pulsed Amperometric Detection Robust & reproducible Analysis Flexcell with exchangeable working electrode

Bisphenol A Catechins Flavonoids and phenols Phenols Antioxidants

Summary

Polyphenols Resveratrol Epicatechin Quercetin other polyphenols

The ALEXYS Carbohydrates Analyzer is a dedicated LC solution for the analysis of sugars and oligosaccharides in a variety of samples.

Carbohydrates Iodide Vitamins A, C, D, E, and K Q10 ubiquinols

Fig. 1. ALEXYS Carbohydrates Analyzer.

Antec Leyden B.V. - Industrieweg 12 - 2382 NV - Zoeterwoude - The Netherlands - info@myantec.com - www.myantec.com Antec (USA) - P.O. Box 111418 - Palm Bay FL 32911 - USA - info.usa@myantec.com - www.myantec.com

220_002 #04

Carbohydrates in Food

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ing in an increase in analyte retention. If the pH > pKa (full disso-

Method
Under alkaline conditions (pH > 12) carbohydrates can be separated by means of Anion-Exchange Chromatography. Carbohydrates are weak acids with pKa values ranging between 12 and 14. At high pH they will be either completely or partially ionised depending on their pKa value. Due to the extreme alkaline conditions only polymeric anionexchange columns are suitable for carbohydrate separation. The retention time of carbohydrates is inversely correlated with pKa value and increases significantly with molecular weight. The elution order of carbohydrates on such anion-exchange columns is usually as follows: sugar alcohols elute first, followed by mono-, di-, tri-, and higher oligosaccharides.

ciation) then the ionic strength will dominate the separation process and the retention decreases. This is illustrated in Fig. 2A. Sodium acetate is commonly used as a ‘modifier’ to decrease the elution time of higher molecular weight carbohydrates allowing faster analysis. Pulsed amperometric detectors are relatively insensitive to ionic strength changes of a sodium acetate gradient, as long as the sodium hydroxide concentration remains constant during the gradient run. High purity grade sodium acetate should be used for the preparation of the mobile phase (impurities can cause large baseline shifts during a gradient run).

Pulsed amperometric detection

E2 (Oxidation Au)
G lu c Fr os uc e L a to s ct e & S uc r
X Axis Title

Potential (V)

A . 50 mM NaO H - 1 mM NaO Ac B . 30 mM NaO H - 1 mM NaO Ac C . 15 mM NaO H - 1 mM NaO Ac al to se

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tsample E3 (Reduction Au)

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Time (s)
Fig. 3. Three-step potential waveform for the pulsed detection of Carbohydrates. amperometric

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15

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M inutes

A 30 m M NaOH - 10 mM NaOAc B 30 m M NaOH - 2 mM NaOAc C 30 m M NaOH - 1 mM NaOAc

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Pulsed Amperometric Detection (PAD) with a gold (Au) working electrode is applied for carbohydrate analysis. A series of electrode potential steps (pulses) enable frequent (typically 1 - 2 Hz)

A
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renewal of the working electrode (WE) surface [1,2]. The...
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