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This paper (open access) recommends the use of sorbitol as an endogenous isotopic reference marker compound for the detection of C4-type sugar adulteration in apple juice.

Apple juice is traded mostly as concentrate because it is more efficient to transport and store than single-strength juice.  It is valued according to its Brix measurement.  There is therefore a motivation to add sugars (increasing the Brix) in order to – in turn – mask dilution. .  Most cheap commercial sugars originate from C-4 plants, and chemical components may therefore have a different carbon isotopic ratio to equivalent chemical components originating from the unadulterated apple juice

The authors present an improved analytical method which utilizes the naturally occurring sorbitol in apple juice as an isotopic reference marker. The method uses liquid chromatography coupled to isotope ratio mass spectrometry (LC-IRMS) to determine the δ¹³C values of the major endogenous sugars in apple juice.

They report  that the δ¹³C value of sorbitol can be measured in the same analytical run as the other major sugar components and remains unaffected by the addition of exogenous C4-type sugars to the apple juice.  A difference between the sorbitol's isotope ratio and that of other components is therefore an indicator of adulteration.

They conclude that this method offers significant advantages over existing approaches, notably by eliminating the need for extensive sample preparation and multiple analytical methods thereby improving both analytical throughput and ease of use.

The authors of this paper include scientists from two of the laboratories in FAN’s Centre of Expertise network; GfL and Fera Science.

Photo by Katrin Hauf on Unsplash

It is very difficult to verify, by testing honey, whether bees have been fed with C3-derived sugar syrups during the foraging season.  Sugar-feeding is not permitted unless over winter to keep the bees alive.

 In this study (open access), the researchers set out to show the potential for discrimination of sugar-fed hives using the non-exchangeable hydrogen isotope ratios on ethanol derived from honey, measured using mass spectrometry (ethanol isotope ratios are the same discriminator that underpin the proprietary SNIF-NMR databases that have been accepted for many years for fruit juice authenticity testing and have also been applied to honey)

 To generate reference samples, 36 genetically similar bee colonies, at a single geographical location and time point, were subject to different controlled sugar feeding regimes.  Four different sugar syrup types were used to represent distinct adulteration scenarios: fructose and glucose syrups derived from C4 plants, invert sugar derived from C3 plants (sugar beet), and sucrose syrup of unknown botanical origin.  Controls were in place to stop the colonies cross-feeding.

 The authors report that Ethanol δD_n values for adulterated samples differed significantly from controls, enabling clear discrimination.  This discrimination could form the basis of a potential classification database.