Examining Food Authenticity with Sensitive Carbohydrate Analysis

HPAE, on the other hand, is a chromatographic technique better suited to separate, detect, and measure carbohydrates as food authenticity markers. It takes advantage of the weakly acidic nature of carbohydrates for highly selective separations at high pH using strong anion exchange stationary phases. At higher pH, carbohydrates are partially ionized and can, therefore, be separated by anion exchange mechanisms.

Coupling HPAE with PAD allows direct quantification of nonderivatized carbohydrates at even low-picomole levels with minimal sample preparation and cleanup. The direct form of analysis precludes any biased selectivity toward certain carbohydrate structures, as may be seen in other analytical methods measuring derivatized sugars. This simplifies method validation and brings much-needed reproducibility to these techniques, enabling intra- and inter-batch testing for quality control.

There are two key reasons why HPAE-PAD is more selective and specific for carbohydrate analysis compared to LC or GC approaches. First, the specific detection voltages used in the pulsed amperometry ensure that it only measures analytes that are oxidizable at those particular voltages. In the case of carbohydrate analysis, the settings provide a sensitivity that is several orders of magnitude greater than other classes of analytes. Second, due to the anion exchange separation, neutral or cationic sample components that may be oxidizable at the same voltages elute into or closer to the void volume of the column, thereby removing any analyte that may otherwise interfere with the carbohydrate analysis.

Food Safety Testing with HPAE-PAD

When it comes to food safety, the data obtained are only as good as the method used. HPAE-PAD methods are commonly used to detect and quantify unauthorized additives in food products that have carbohydrates as their quality markers. Additionally, the method is regularly used to characterize the carbohydrate components present in the food sample to gain deeper insights into their composition, serving as another testing parameter for future measurements. Below, we have listed how HPAE-PAD can be used to perform safety testing and combat food fraud in popular food items.

Honey. Composed of several sugars based on its floral source, honey is tested for adulteration using sucrose as its quality indicator. Adding cheap sweeteners, such as cane sugar or refined beet sugar, can artificially increase the levels of sucrose in honey. The Codex Alimentarius Committee on Sugars has, therefore, specified the maximum value of sucrose as 5 g in 100 g of honey. Carbohydrate analysis with HPAE-PAD can be used to measure these parameters as well as determine the floral origins of honey, using a few minor sugars as a “fingerprint.” Using the Thermo Scientific Dionex CarboPac PA210-4μm column in an HPAE-PAD protocol allows for the separation of 15 sugars in honey with minimal sample preparation, 80-120% precision and accuracy, and a detection limit of as low as 10% adulteration with added syrups.

Agave syrup. Another food product that has recently become a target for food fraud due to its growing popularity is agave syrup. An alternative to traditional sweeteners, such as table sugar and honey, agave syrup has a low glycemic index, causing a slower rise in blood glucose and insulin levels. As most of its sugars are in fructose form with very little glucose, adulteration with high fructose corn syrup is common. The main producer of agave, Mexico, has recently created a governmentally approved guideline for the characterization of pure agave syrup. In the method prescribed by the Norma Oficial Mexicana, HPAE-PAD is used to determine levels of the main sugars (fructose, glucose, and sucrose), polyols (sorbitol, mannitol), and 5-hydroxymethyfural. After the agave syrup is diluted with water, the carbohydrate profiles are analyzed before and after enzymatic hydrolysis with amyloglucosidase and fructanase to measure the content of sugars as well as fructan.