It is an analytical challenge to differentiate natural raspberry flavouring from its synthetic analogue when testing a finished food product. One analytical marker is α-ionone. In natural flavouring this compound is predominantly a single enantiomer (a "mirror image" structural arrangement), whilst in the artificial version it is a racemic mix (both mirror images in equal proportion). But analytical differentiation needs specialist (chiral) chromatography columns and sometimes better sensitivity than standard aroma extraction such as SPME-GC can provide.
In this paper (open access) the authors use hydrodistillation extraction and concentration using a Clevenger apparatus. They optimise the conditions for various sample types such as icecream and syrups. They then couple this witht chiral GC-MS analysis.
They report that their method enables the precise separation and quantification of the R- and S- enantiomers of α-ionone, and the enantiomeric ratio is used to verify authenticity. It enabled detection of trace concentrations of α-ionone (LOD 5 × 10−4 mg/kg, LOQ 1.7 × 10−3 mg/kg) in various food samples, minimized solvent consumption and allowed for the accurate quantification of minor S-enantiomers without the need for isotopically labeled standards.
As a proof of concept, they applied the method to 13 commercial food samples. They report significant differences between natural and synthetic aromas, with the majority of products containing synthetic racemic mixtures.
They conclude that their method represents a practical tool for routine control of the authenticity of raspberry aroma in foods, including heterogeneous and fat-rich matrices.
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