Examining Food Authenticity with Sensitive Carbohydrate Analysis

Fruit juices. The billion-dollar fruit juice industry often encounters dilution and blending with inexpensive and synthetic sweeteners, a ploy designed to achieve higher margins and larger economic gains. A common adulterant known as medium invert sugar, in which one half of the sucrose has been hydrolyzed to glucose and fructose, closely matches the composition ratio of approximately 1:1:2 (glucose: fructose: sucrose) found in orange juice. When cane sugar is the source of the invert sugar, stable isotope ratio analysis (SIRA) can be used to detect adulteration due to the differing ratios of 13C:12C in orange juice and cane sugar; however, if beets are used to produce the invert sugar, the 13C:12C ratio between orange juice and beet sugar do not differ much as the sugars are produced using similar metabolic pathways. In this case, SIRA can no longer detect adulteration by beet sugar, providing a convenient loophole in food fraud.

Scientists have resorted to HPAE-PAD to characterize beet invert sugar and discover several sugar components that are not present in orange juice. One such sugar not found in pure orange juice is raffinose, a trisaccharide of D-glucose, D-fructose, and D-galactose, which has been used as an adulteration marker for orange juice. Additionally, the signature pattern of late-eluting components appearing at about 60 minutes during the HPAE-PAD run can also be used to identify adulteration.

Coffee. Carbohydrates also serve as tracers to assess the authenticity of instant coffee. Although an unlikely candidate for sugar analysis due to its characteristic bitter taste, at least 50 percent of the dry weight of raw coffee beans comprises coffee carbohydrates. As these undergo Maillard reaction during the roasting process, they contribute to the flavor, aroma, and viscosity of coffee. An HPAE-PAD-based method to determine the free and total carbohydrates in instant coffee has been prescribed by the Association of Analytical Chemists (AOAC) Official Method 995.136 and is currently used by the British Standards Institution. In a recent application study, the AOAC method was tested using the Thermo Scientific Dionex CarboPac SA10 column. The former method, which typically has a run time of 80 minutes, was made significantly faster by using the column. The quicker method had a run time of 10 minutes, only needed deionized water for continuous operation, and offered the same level of accuracy and sensitivity, differing only in its total analysis time and number of resolved peaks for coffee carbohydrate analysis.

All the food testing examples mentioned above justify the argument that, with the increasing demand for reproducible, fast, and simple methods to profile a wide variety of analytes in the food industry, HPAE-PAD has steadily emerged as a reliable method of choice to analyze carbohydrates.

Better Methods, Safer Food

As traditional methods used in the food industry start becoming outdated, new and problematic adulterants that are similar in structure to the genuine components can sneak into the food industry by taking advantage of either inadequate sensitivity or lack of specificity. Food testing laboratories will need to continually evaluate, test, and validate new methods to stay ahead of food fraud, while keeping up to date with regulations. Similarly, upgrading conventional methods with the latest technology makes them more robust and productive. Choosing the most appropriate method to accurately detect carbohydrate-based authenticity markers, such as HPAE-PAD, will result in safer food for the community and sustain consumer trust with the manufacturer.

Man is product marketing manager, IC/SP, chromatography and mass spectrometry for Thermo Fisher Scientific. Reach her at [email protected].