Natural aroma chemicals for use in foods and beverages - Natural Food Additives, Ingredients and Flavourings - page 221

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13 C isotopic ratio mass spectrometry (IRMS)
All chemical reactions differentiate to some extent between isotopes of the same
element. This phenomenon is related to the zero-point energy of the chemical bond,
which in turn refl ects the mass of the atoms thus combined. Hence the greatest
difference occurs when hydrogen is replaced by deuterium, as the change in mass is
the greatest. But it is also observable with other light elements, especially carbon,
where 13 C is ca. 1% of all terrestrial carbon. This can enable us to determine the
nature of transformations that have taken place in the production of a specifi c material.
In the context of natural aroma chemicals this can, in certain cases, enable us
to differentiate between chemical and enzymatic conversions, and in the latter
case, between enzymatic and microbial conversions, and between different types
of organism. One of the most useful makes use of the different routes plants use
in photosynthesis; the three routes, C3 and C4, so-called as the carbon dioxide is
fi rst incorporated into a C3 and a C4 chain respectively, and the less common
CAM pathway (named after the type of plant where it was fi rst recognised and the
storage of CO 2 as an acid). All three pathways 'disfavour' incorporation of 13 C,
but to different degrees. This difference, delta 13 C (or d13C) is the ratio of stable
isotopes 13 C: 12 C, expressed in parts per thousand (per mil, ‰) when compared to
the ratio in the mineral PeeDee belemnite. Typical values for bulk 13 C ratios are
−10 to −16 for C4 plants, −23 to −32 for C3 plants, with CAM plants having a
wider range, ca. −12 to −30. It is important to note that this test does not of itself
indicate natural status, as 'fossil fuels' are of organic origin and themselves have
a range of ca. −15 to −33 (Asche et al. 2003).
One of the most clearest differentiated material is vanillin [10.47]. The vanilla
plant ( Vanilla planifolia or Vanilla tahitensis ) is in fact a tropical orchid, which makes
use of the CAM pathway, and the 13 C signature of 'vanillin ex vanilla' is typically in
the -12 region, making it clearly distinguishable from material of petrochemical
origin (ca. −24) and that derived from ferulic acid [10.48]. The latter is usually
obtained from rice, a C3 plant, and has a delta 13 C value more in the region of −31.

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