C3, C4 or CAM plants (see Botanic Sources: C3, C4 and CAM
Plants), where it is ester-linked to polysaccharides. 12 As such, it
also occurs in common agricultural residues such as cereal bran.
However, it does not exist in a free form, but as a glycosidic bond
with carbohydrate chains in the cell wall; therefore, hydrolytic
methods, either enzymatic or alkaline, are used to release it.
The three photosynthetic processes from C3, C4 or CAM
plants will generate isotopic effects, in particular the 13C isotopic
effect, which helps traceability of the botanic origins.
How to Authenticate Vanillin from C3 and C4 Plants
As previously mentioned, natural vanillin obtained via the bioconversion of ferulic acid from rice, a C3 plant, is the only natural
vanillin from a non-vanilla source available at present.
Natural vanillin obtained via the bioconversion of ferulic
acid from maize, a C4 plant, has been the subject of studies
in recent years. Initial investigations were carried out in 1990
within the framework of the FAIR Consortium, involving the
INRA (Institut National Recherche Agronomique) and, among
Isotopes and Isotopic Effects
Isotopes are species of the same element differing by the
number of neutrons. The natural average proportion of
common isotopes is given in F- 2.
The mass difference between isotopes of the same element
may be sufficient to induce differences in physical and
chemical properties. This is why the natural abundance of
isotopes is not uniform around the world in the biosphere and
Natural isotopic variations observed in chlorophyll tissues
versus atmosphere are due to fractionation phenomena, also
called isotopic discrimination, occurring between “light”
molecules, such as 12CO2 and “heavier ones,” such as 13CO2
and 14CO2, during carbon assimilation at light. As a matter of
fact, the isotopic mass difference between different types
of CO2 molecules leads to differences in behavior such as
lowering of gaseous diffusion through the stomatic pores
of leaves (13CO2, being slightly heavier, will diffuse less
rapidly than 12CO2), lowering of the reaction rate constant of
enzymatic reactions. Thus, photosynthesis discriminates the
light isotope 12C to the detriment of the heavy isotopes such
as 13C and 14C in leaves. The consequence is a decrease in 13C
(and 14C) of the plant organic matter, compared to the carbon
of atmospheric CO2.
Away from industrial activity, atmospheric carbon dioxide
displays a mean isotopic deviation of about d13C = - 8‰ all over
the world. The effect of CO2 integration by the plant leads to a
decrease of 13C isotopic ratio in plants of about - 20‰ for plants
with a C3 photosynthetic pathway. The C3 photosynthetic
pathway is very discriminative toward 13C, whereas C4 plant
discrimination toward 13C is lower. As a result, the 13C/12C
isotopic deviation is only lowered by about - 3-4‰. 13
F- 2. Natural average proportion of common isotopes; source: Eurofins Analytics France
F- 3. Mean d13C isotopic deviation (in ‰) found in nature; source: “L’isotope: traceur d’origine.
Distribution isotopique dans les composés naturels,” G Remaud and S Akoka