Electrochemical HPLC Detection of Sugars in Foods and Beverages

For various reasons including genetics, some people need to avoid some or all sugars. This may be due to serious allergies or intolerances. Lactose, and its monosaccharide galactose, are sugars which are particularly common in intolerance and serious allergic situations. 

 
Consequently, a large number of dairy origin foods and beverages have been developed, where lactose is normally removed by enzymatic, chromatographic, ultrafiltration, centrifugation and hydrolysis techniques.

For various ethical, medicinal and religious reasons, there is also a growth in the availability of soya, rice, almond, soy protein isolate and coconut milk types of beverages and foods. These products naturally contain none or trace levels of lactose and galactose.

These dairy origin and alternative milk beverages and foods, have triggered the debate of the definition of ‘lactose free’. Some schools of thought state that an infant formula milk lactose content, of less than or equal to 1,000 ppm may be considered to be lactose free. Others state that no lactose or galactose should be present, however, there should be a definition of which analytical method/s are used to define a zero presence.

And of course, the maintenance of blood glucose levels in diabetics is paramount. In particular, knowledge of the glucose levels in chocolate and confectionary for diabetic consumers, is vital.

Another debate rages over the role and ingestion of fructose, so even fruit and pure fruit juices are not immune from scrutiny. Some people even have a profound physiological intolerance to fructose. 

Add to this, the increasing controversies and taxation levy issues, over the consumption of soft drinks containing added sugars. Here, the financial implications of total sugar content can be far reaching. Incidentally, although drinks which have a high milk content may not be subject to taxation levies, as no sugar is added to them, one wonders how non-dairy milk glucose energy drinks, are or would be categorised. 

Hence there is a need for laboratories to measure and certify the concentration of lactose galactose, glucose, fructose, sucrose and other sugars and sugar alcohols, to extremely high sensitivities.

Within laboratories dedicated to production/processing environments, accurate, highly sensitive, fast, reproducible, reliable and specific measurements of sugars and sugar alcohols are required for samples in a variety of matrices, particularly those involving fats and oils.

To discuss how you can overcome these challenges and deliver reliable results, we spoke to Ade Kujore from Cecil Instruments.

JR: Why is electrochemical HPLC analysis superior to alternative methods for detecting sugars in food?

AK: Several analytical methods are considered in the detection of sugars in foods and beverages. Gravimetric and Infra-Red spectrophotometer methods are not specific for the various sugars and sugar alcohols. Enzymatic methods where the final results are measured with UV/Visible spectrophotometry have sensitivities of around 100 ppm, but these methods often require a great deal of sample pre-treatment.

Capillary electrophoresis with electrochemical detection does produce higher sensitivities of around 100 ppb and can be specific. However, this technique and its instrumentation, is not as common.

Liquid chromatography/Mass spectrometry will differentiate between the various sugars and sugar alcohols to very high degrees of sensitivity, but can be a complex and relatively expensive technique.

HPLC can produce accurate, fast, reproducible, reliable, and sensitive detection of specific sugars and sugar alcohols without too much sample pre-treatment. The choice of HPLC detector is important, the limit of quantitation of refractive index detection for specific sugars is around 100 ppm, so does not provide sufficient sensitivity in the case of the ‘sugar free’ analyses.

HPLC with gold electrode pulsed electrochemical detection is highly sensitive and is specific. It is a relatively inexpensive and easy to use technique, very much suited to determination of ‘sugar free’ and lactose free analyses.

JR: What challenges can your Adept and Q-Adept HPLC systems help food analysts to overcome?

AK: Food analysts often require sensitive, versatile, reliable, accurate, forgiving, quick change–over instrumentation with ease and speed of analysis. The samples matrices are often complex, so sample pre-treatment is often required. The advent of solid phase extraction (SPE) techniques has been a great help. Often there is a fairly high turnover of staff, so instrumentation should be easy to master and accurate records of usage need to be adequately retained.

Robust and long-lasting, modular Adept and Q-Adept HPLC systems, are flexible, with good choices of low noise and drift detectors, autosamplers including SPE, and ease of use and maintenance. The systems will also easily incorporate ancillary instrumentation, such as post column reactors and column heater/chillers.

The easy to use, but comprehensive 21 CFR part 11 compliance PowerStream chromatography software will help in ensuring that foods, beverages and products are tested to internationally accepted standards. For newcomers to a given laboratory, the software learning curve is short.

A Cecil Instruments’ ternary gradient Adept HPLC gold electrode pulsed electrochemical detection system, plus a suitable column heater/chiller and a degasser, will provide for the highest of sensitivities in the determination of sugars and sugar alcohols. In addition, an optional AutoQuest autosampler may be used. 

 
As these HPLC systems may also be coupled to other detectors, such as refractive index, fluorescence, UV/Visible, Scanning UV/Visible and conductivity, other food and beverage related analyses may be performed. Example analyses include, added sugars in soft and alcoholic drinks, aflatoxins in wheat and nuts, polyaromatic hydrocarbons (PAHs) in feed water and phosphoric acid in cola beverages.

JR: Are your instruments sensitive enough to meet all current regulatory requirements?

AK: All of the Cecil instrumentation, including the UV/Visible spectrophotometers, provide in excess, for the required levels of sensitivity stipulated by the regulatory methods which apply to their instrument classes.

For newly developed food and beverage related analytes, which have not been registered or placed into common use, new analytical methods may be required. Cecil instrumentation may be used to develop those methods. As sample-treatment may often be required, such as in pesticide residue analysis, pre-concentration of samples may be coupled with the extremely low noise of the Cecil detectors, to achieve the required levels of sensitivity.

JR: Last year, Cecil Instruments introduced an all new electrochemical detector. How has this new product been received?

AK: This electrochemical detector has proved to be brilliant. It has already been requested in many countries throughout the world, for use with a wide range of analyses. Within the food and beverage industry, it has been popular for use in the isocratic pulsed detection of sugars and sugar alcohols and for use with a ternary HPLC system, as required by a regulatory method. Within the forensics field, it has been used to determine adrenaline and residual cyanide levels.

The Cecil electrochemical detector may be added to many third party liquid chromatography systems. It may also be operated in a choice of three modes, DC, scanning DC and pulsed amperometric. Gold, glassy carbon, silver and platinum working electrodes may be selected, together with reference electrode options.

Sensitivities of 10 to the power of minus 15 mol have been achieved with simplicity.


Ade Kujore
Cecil Instruments Limited
Milton Technical Centre, Cambridge CB24 6AZ
United Kingdom

email:- info@cecilinstruments.com
telephone:- +44 (0) 1223 420821
web site:- www.cecilinstruments.com